Effects of edge and internal patchiness on habitat use by birds in a Florida hardwood forest

MISSING IMAGE

Material Information

Title:
Effects of edge and internal patchiness on habitat use by birds in a Florida hardwood forest
Physical Description:
vi, 109 leaves : ill. ; 28 cm.
Language:
English
Creator:
Noss, Reed F
Publication Date:

Subjects

Subjects / Keywords:
Birds -- Effect of habitat modification on   ( lcsh )
Habitat (Ecology) -- Modification   ( lcsh )
Birds -- Habitat   ( lcsh )
Habitat (Ecology) -- Florida -- San Felasco Hammock State Preserve   ( lcsh )
Wildlife management -- Florida   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1988.
Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by Reed F. Noss.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001133739
notis - AFN1130
oclc - 20159403
sobekcm - AA00004820_00001
System ID:
AA00004820:00001

Full Text














EFFECTS OF EDGE AND INTERNAL PATCHINESS
ON HABITAT USE BY BIRDS IN A FLORIDA HARDWOOD FOREST







By

REED F. NOSS


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA


1988















ACKNOWLEDGMENTS


I thank the members of my supervisory committee, Drs.

Ronald F. Labisky (Chairman), Michael W. Collopy, and John G.

Robinson in the Department of Wildlife and Range Sciences,

and Drs. Peter Feinsinger and Brian K. McNab in the

Department of Zoology, University of Florida, for guidance

and comments throughout this study. Drs. T.C. Edwards and

K.M. Portier and Mr. Tim O'Brien provided statistical advice,

and Dr. L.D. Harris provided helpful dialogue throughout the

course of this study. Ms. Candy Hollinger drew all figures.

Funding was provided by the Alachua Audubon Society, the

Frank M. Chapman Memorial Fund, the Florida Ornithological

Society, the Josselyn Van Tyne Memorial Fund, and the

Department of Wildlife and Range Sciences, University of

Florida.

I owe much gratitude to my wife, Myra, and daughter,

April, for their steadfast patience during the countless

hours I spent in the field and behind the PC. This

dissertation is dedicated to my mother, Margaret Johnson Noss

(1923-1987), who always encouraged my interest in natural

history, and to my father, James Frederick Noss, who

continues to help and encourage me today.
















TABLE OF CONTENTS



Page

ACKNOWLEDGMENTS...........................................ii

ABSTRACT ...................................................V

INTRODUCTION.......................... .....................1

STUDY AREA AND METHODS......................................5

Study Area.............................................. 5
Bird Surveys..........................................10
Habitat Analysis.....................................12
Data Analysis.........................................17

RESULTS.....................................................20

Habitat Description..................................20
Birds..................................................24
Edge Effects ..........................................26
Bird Densities in Edge versus Interior Plots.........43
Internal Patchiness and its Relation to Bird
Densities and Edge Effect..........................43
Patterns at the Between-Plot Scale...................56
Responses of Individual Species to
Habitat Heterogeneity..............................60

DISCUSSION................................................64

Bird Responses to Forest Edge and Internal
Patchiness: A Matter of Scale?....................64
Edge Relations..................................................66
Patchiness Relations.................................71
Management Implications...............................75
A Final Comment on Scale and Observation.............80

LITERATURE CITED............................................83

APPENDIX

I PROPORTIONAL RELATIVE ABUNDANCES OF TREE AND
SHRUB-LEVEL WOODY SPECIES.........................95

iii










Page

II BIRD SPECIES OBSERVED IN STUDY PLOTS AND THEIR
EDGES IN SAN FELASCO HAMMOCK, 1985-86 ............ 101

BIOGRAPHICAL SKETCH... ..................................108











Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

EFFECTS OF EDGE AND INTERNAL PATCHINESS
ON HABITAT USE BY BIRDS IN A FLORIDA HARDWOOD FOREST

By

Reed F. Noss

August, 1988

Chairman: Dr. Ronald F. Labisky
Major Department: Wildlife and Range Sciences
(Forest Resources and Conservation)

Effects of edge and internal patchiness on habitat-use

by birds were studied in an old-growth hardwood forest in

northern Florida. Registrations of birds during the breeding

seasons of 1985 and 1986, fall 1985, and winter 1986 were

mapped in 12, 5.0-ha plots that abutted edge and in 3, 5.0-ha

interior plots >700 m from edge. Habitat-use patterns of 27

avian species were analyzed at within-plot (0.5-ha subplots)

and between-plot observation scales. Forest edges, canopy

gaps, and shrubby seepage areas ("bayheads") exhibited high

densities of birds within plots, but with seasonal and

species-specific variations. Density of birds at 0-50 m from

edge was significantly (P < .05) greater than in distance

zones farther from edge in 6 of 12 edge plots, for all

seasons combined. All 27 species used both interior and edge

habitat, but 12 species were generally attracted to edge, 11

were indifferent, and 4 avoided edge. Edge effects were









greatest during the breeding seasons in plots with high-

contrast edges, and in east-facing edges on sunny winter

mornings (suggesting a microclimatic influence). Attraction

to edge in the breeding seasons was stronger in subplots

lacking gaps and bayheads than in more heterogeneous

subplots. In interior plots and in all plots combined,

regression models containing indices of patchiness

(especially gap/bayhead area) explained 5-71% of the

variation in bird density, depending on season; strongest

relationships occurred during the breeding seasons.

In between-plot analyses, neither bird density nor

richness differed between edge plots and interior plots, or

between patchy plots and more homogeneous plots (except that

richness was correlated with CV of shrub density, one measure

of patchiness). Birds used gaps, bayheads, and edges

extensively within plots, but did not concentrate in areas of

the forest near edge or with more gap/bayhead area. Hence,

both edge effects and "patch effects" may be dependent on

observation scale. Allowing forests to mature to naturally

patchy old-growth may be a more prudent management strategy

than maintaining artificial openings or edges.















INTRODUCTION


No natural community is homogeneous. Yet, a tradition

in community ecology has been to select the most uniform and

undisturbed areas as study sites (Forman and Godron 1981,

Noss 1987a). Although recognition of natural disturbances

and spatiotemporal mosaics is not new (e.g., Cooper 1913,

Watt 1925, 1947), selection of heterogeneous systems as units

of study only recently has become popular in North American

ecology (Forman and Godron 1981, 1986, Risser et al. 1984,

Pickett and White 1985, Urban et al. 1987). The increasing

acceptance of landscape ecology follows the recognition that

many organisms depend on environments that are frequently

disturbed and composed of multiple habitats (White 1979, den

Boer 1981, Karr and Freemark 1983, May 1986, Noss 1987a,

Merriam 1988).

Habitat heterogeneity occurs at many spatial scales, as

an expression of environmental gradients and resource

patchiness, and disturbances that are patchy in time and

space. Not only does landscape pattern affect population

distribution, but the scale at which patterns are sought will

determine what patterns are detected (Wiens 1985, 1986, Wiens

et al. 1987). Coarse-grained landscape heterogeneity











(macroheterogeneity; Forman and Godron 1986) is generated by

large natural disturbances as well as by anthropogenic

habitat modification and fragmentation. Patches in

macroheterogeneous landscapes, e.g., interspersed woodlots,

crop fields, pastures, ponds, and housing developments, are

easily recognized as separate habitats. Boundaries between

habitats at this scale are usually called "edges." In

contrast to the mosaic of habitats at a landscape scale,

fine-grained patchiness (microheterogeneity; Forman and

Godron 1986) occurs within what are usually recognized as

distinct habitats or community-types.

Habitat selection, best studied for birds (Cody 1985),

involves responses to habitat cues at several spatial scales

(Hilden 1965, James 1971, Hutto 1985, Wiens 1985). Elements

of habitat heterogeneity at different scales determine the

distribution of bird populations, territories, and activity

within territories. Over a range of habitats, bird species

diversity is positively correlated with complexity of the

vertical foliage profile (MacArthur and MacArthur 1961,

Recher 1969, Karr and Roth 1971). Horizontal complexity or

patchiness of vegetation, however, may be more important than

vertical profiles in determining bird species composition and

diversity within study sites (MacArthur et al. 1962, Roth

1976, 1977, Wiens 1985, Freemark and Merriam 1986). An

important element of within-habitat patchiness is treefall

gaps. Gaps often contain high densities of resources such as











insects and fruits, and therefore attract an abundance of

birds (Blake and Hoppes 1986, Martin and Karr 1986).

Patchiness at a coarser scale may affect bird

distribution within habitats, i.e., the well-known "edge

effect." Many bird species are attracted to edges, but a few

species are repelled and some are indifferent (Whitcomb et

al. 1981). Although maximizing edge habitat has been a

common wildlife management prescription (Thomas et al. 1979),

this policy has been criticized in recent conservation

biological literature because of documented deleterious

effects on forest interior species (Whitcomb et al. 1976,

1981, Gates and Gysel 1978, Noss 1981, 1983, Brittingham and

Temple 1983, Lovejoy et al. 1986, Wilcove et al. 1986).

Unfortunately, studies of edge effects on birds generally

have ignored habitat patchiness within forests. Gates and

Gysel (1978) hypothesized that edges attract many passerines

because they contain structural cues similar to those of the

mixed life-form habitats in which these species evolved.

Before European settlement, the eastern deciduous forest

landscape was old-growth (best understood as a mosaic of

developmental stages, rather than just the mature stage). In

contrast to the generally even-aged, close-canopied,

secondary forests in which edge effects usually have been

studied, old-growth is horizontally patchy with numerous gaps

in various stages of post-disturbance regeneration (Bormann

and Likens 1979, Runkle 1985, Whitney 1987).











Does edge effect diminish in forests with increased

internal patchiness such as that associated with treefall

gaps? Or conversely, do artificial edges disrupt the normal

distribution of bird activity with respect to internal

patchiness? This study simultaneously considered effects of

edge and internal patchiness on habitat use by birds in an

old-growth hardwood forest in north central Florida.

Specific objectives were (1) to test the null hypothesis of

uniform distribution of birds with distance from edge for

different species, seasons, and edge types; (2) to

investigate the relation between bird density and habitat

heterogeneity (as measured by several indices) in 5.0-ha

plots that abutted edge, and in 5.0-ha "control" plots

located at distances > 700 m from edge; (3) to identify bird-

habitat heterogeneity relationships at within-plot and

between-plot observation scales; and (4) to determine

interacting effects of internal habitat heterogeneity and

edge on bird habitat-use.















STUDY AREA AND METHODS


Study Area

San Felasco Hammock State Preserve (29045' N, 82030' W)

is located 8 km northwest of Gainesville, Alachua County,

Florida. Over half of the 2500-ha preserve is mesic hammock

(a mixed-species, predominantly hardwood forest), considered

the climax community of northern Florida by many authors

(Harper 1905, Quarterman and Keever 1962, Monk 1965). In

Florida, fire, interacting with slope-moisture gradients, is

a primary determinant of plant distribution; hammocks are

naturally restricted to ravines and sinkhole slopes, islands,

peninsulas, and other sites of reduced fire frequency (Harper

1911, Clewell 1981, Platt and Schwartz in press). The high

species richness (probably the largest stand-scale number of

woody species in the continental United States) and

structural heterogeneity of north Florida hammocks derive

from a complex disturbance regime which creates numerous gaps

and maintains nonequilibrium populations of plants (Platt and

Schwartz in press).

The study site was chosen for its size (with gradients

from edge to deep interior habitat) and old-growth character.

San Felasco Hammock is probably the largest remaining mesic











hammock in the hammock belt that extends along the central

ridge of the Florida peninsula (Ewel and Simons 1976, Platt

and Schwartz in press). The vegetation and flora of San

Felasco Hammock were described by Ansley (1952) and Dunn

(1982), and summarized by Skeate (1987). The woody flora of

this mesic hammock is extremely rich, with as many as 20 tree

species per ha (Noss, unpublished data) and 50 "canopy

potential" tree species (Dunn 1982). Dominant canopy trees

include Ouercus hemisphaerica, Carya glabra, Magnolia

grandiflora, Quercus nigra, Quercus virginiana, Pinus glabra,

Liquidambar styraciflua, Quercus michauxii, Quercus austrina,

Quercus shumardii, Quercus falcata, Acer barbatum, Fraxinus

americana, Carva tomentosa, and Tilia caroliniana. San

Felasco is near the southern range limit for many plant

species (R. Simons, personal communication), and for several

forest-interior bird species that are known elsewhere to be

sensitive to forest fragmentation and edge effects (cf.

Whitcomb et al. 1981).

The portion of San Felasco Hammock in which study plots

were selected was mature mesic hammock, as mapped by Dunn

(1982). This forest has been selectively logged (Dunn 1982),

but is essentially old-growth, with an uneven age composition

of trees, a pit-and-mound microtopography, and a horizontal

mosaic pattern enriched by treefall gaps, sinkholes, seepage

areas with dense broad-leaved evergreen trees and shrubs

(bayheads), and other patches. The mesic hammock in San











Felasco abruptly borders several other habitat types. Some

of these sharp edges are natural (e.g., with adjoining

sinkhole marshes and pinelands), whereas others are

artificial (e.g., with oldfields and cleared powerline

rights-of-way).

Five major edge types were identified: hammock/

oldfield; hammock/open pine plantation; hammock/longleaf

pine-turkey oak (sandhill); hammock/herbaceous marsh; and

hammock/open powerline right-of-way. These edge types were

the strata from which 12, 5.0-ha (200 m x 250 m) plots were

selected randomly, with the restriction that the central

transects of plots be at least 300 m apart to avoid double-

counting of birds. Two plots were selected to represent each

edge type, except that 4 plots (2 with southwest-facing edges

and 2 with northeast-facing edges) were selected from the

powerline right-of-way. Hence, each of 12, 5.0-ha plots

abutted an open habitat along a 200-m edge, and extended 250

m into the hammock (Fig. 1, Table 1). In addition, 3

"control" plots of 5.0 ha each were selected randomly in

interior forest >700 m from any abrupt edge (Table 1). Each

5.0-ha plot was divided into 10, 0.5-ha subplots for data

compilation and analysis (Fig. 1). A central transect line

for bird surveys extended 250 m through each plot, with

observation posts flagged every 25 m. Prominent habitat

features such as major gaps and sinks, streams, trails, and






































r-



In







0
O1

L


0


I

II



--00

OJ


0
o




I


In

0--
O


I
*-






I-




1-

0


0


oo)4
Cu -,r-
C 0O




I.,-.
4M
> 0
E-i .

QLr 3
C O


- 0I


So
re O
a3 0

4--1 0
co o CO




co c








44 C
tO I Q)-
,o Cn ,

o ca



CE

4-i
O 4 r-4
00
E-





.ro to



c-4 Wo
C Q) C


CO


*4 0
C- C
*I-
t3 U *
. U~- 4Ji-





u')
cO







0









TABLE 1. Individual 5.0-ha study plots and their transect
orientations, San Felasco Hammock, Florida. All edge
plots are perpendicular to edge,whereas interior plots
are perpendicular to narrow trails.


Edge Plots (N = 12)

PL1 (Powerline 1): 300

PL2 (Powerline 2): 2200

PL3 (Powerline 3): 2200

PL4 (Powerline 4): 400

MA1 (Marsh 1): 700

MA2 (Marsh 2): 2800

SA1 (Sandhill 1): 1100

SA2 (Sandhill 2): 3400

PP1 (Pine Plantation 1): 2700

PP2 (Pine Plantation 2): 2700

OF1 (Oldfield 1): 2700

OF2 (Oldfield 2): 2700

Interior Plots (N = 3)

IF1 (Interior Forest 1): 2700

IF2 (Interior Forest 2): 3200

IF3 (Interior Forest 3): 1800











big trees were mapped prior to the study to facilitate

accurate location of birds.



Bird Surveys

Birds were surveyed by use of a strip-map method (Emlen

1984; similar to the "plot mapping" of Christman 1984), which

is essentially a combination of transect and spot-mapping

techniques. The method is observer-specific, with plot width

dependent on the detection abilities of an individual

observer. The 12 edge plots were sampled in spring 1985

(S85: 18 censuses each from 5 March-18 June), fall 1985 (F85:

6 censuses each from 12 September-30 November), winter 1986

(W86: 6 censuses each from 11 January-27 February) and spring

1986 (S86: 12 censuses each from 2 March-19 May). The 3

interior (control) plots were censused in W86 and S86; these

censuses were conducted during the same calendar period and

at the same frequency as for edge plots. Demarcation of

seasons was necessarily arbitrary. Breeding seasons

(indicated by singing and other territorial behavior) of

permanent resident passerines and woodpeckers begin in this

region in January and February, at the same time when

wintering species reach peak abundance. Summer residents

j begin breeding in March and April, coinciding with peak

densities of migrants, often of the same species.

Daily censuses were confined to the period between

sunrise and 3 h post-sunrise. Three or 4 plots were censused











per census day, with plot order alternated to assure

equivalent temporal coverage. Censuses were not conducted if

weather conditions were adverse (i.e., rain or strong winds).

Auditory and visual observations of birds were mapped

during each census. A registration was defined as any

auditory/visual observation within the study plot, excluding

birds flying above the canopy. Density refers to the sum of

registrations recorded in a defined area (e.g., a subplot).

Birds using the edge (or plot boundary, for interior plots)

were mapped as each transect starting point was approached;

thereafter, registrations were recorded during 3-min periods

at each 25-m interval observation post. Registrations also

were recorded while walking slowly between observation posts.

Bird movements were recorded as separate registrations if

they were >25 m from the previous registration; however,

movements that appeared to be in response to the observer

(either attraction or avoidance) were not recorded.

Preliminary censuses indicated that most resident

(breeding, winter, and permanent) species could be detected

by ear up to 100 m from the central transect line; thus,

registrations were mapped within 100 m on each side of the

transect. The analysis assumed equivalent detectability in

all subplots of each plot, in accordance with equivalent

sampling effort. Because comparison of abundances among

species was not an objective, the analysis did not assume

that species were equally detectable, or that detectability











was constant from 0-100 m; thus, no coefficients of

detectability (Emlen 1971) were calculated. Resident species

with poor detectability (e.g., Blue-gray Gnatcatcher) were

excluded from analysis. Also excluded from analysis were

those species with sample sizes <30 in the 12 edge plots

(single-species analyses were performed for combined edge

plots and for all 15 plots combined), and one abundant winter

resident (Yellow-rumped Warbler) that usually occurred in

sporadic, itinerant flocks. Species with large territories

or ranges (raptors, jays, and crows) were not mapped or

analyzed. Breeding status was based on Florida Breeding Bird

Atlas criteria (Noss et al. 1985). Species richness of

probable and confirmed breeders with at least 25% of a

territory in a plot was recorded for each plot in 1985 and

1986.



Habitat Analysis

The objective of habitat analysis was to measure

parameters of forest microheterogeneity proposed in previous

studies to be important to birds, including diversity of

vertical profiles, spatial variability in tree and shrub

dispersion, variation in shrub density and canopy openness,

floristic (tree and shrub) diversity, and proportion of plot

occupied by canopy gaps and bayheads (Table 2). These

attributes of heterogeneity were measured in summer and early

fall 1986 at 2 scales: 0.5-ha subplot (for within-plot










TABLE 2. Habitat variables measured for each 0.5-ha subplot
(from 10 point-quarter samples/subplot) and/or each 5.0-ha
plot, San Felasco Hammock, Florida. See text for further
explanation.

Plot (P) or
Variable Measurement definition Subplot (SP)


median distance (m) from edge
for each subplot


DIST


VT



VS


VTS


DENS



VSD


OPEN




VCO


GAB GA + GB


coefficient of variation (CV) of
distances to nearest trees in
point-quarter samples

CV of distances to nearest "shrubs"
in point-quarter samples

CV of distances to nearest trees or
shrubs in point-quarter samples

mean number (N) of shrub stems in
quarter-circles within 2 m of each
sample point

CV of shrub density (DENS)
measurements

mean canopy openness (%), or converse
of canopy density, as measured by
spherical densiometer at each
sample point

CV of canopy openness (OPEN)
measurements

Shannon diversity (H' logl0) of tree
species from point-quarter samples

H' of shrub species from point-
quarter samples
H' of vertical foliage profiles at
each sample point

proportion of area in canopy gaps
with shrub-sapling growth generally
< 2 m

proportion of area in canopy gaps
with shrub-sapling growth >2 5 m


SP and P



SP and P


SP and P


SP and P



SP and P


SP and P




SP and P


SP and P
(separate)

SP and P
(separate)
SP and P
(separate)

SP and P



SP and P


SP and P


HPD


GA



GB










TABLE 2--continued


Plot (P) or
Variable Measurement definition Subplot (SP)


proportion of area in bayhead
vegetation

GAB + BAY (sum)

largest single canopy gap in
plot (m2)

number of tree species (S) in plot,
from point-quarter samples

number of "shrub" species (S) in
plot, from point-quarter samples


SP and P


S and P

P


P


P


BAY


GAPBAY











analysis) and 5.0-ha plot (for between-plot analysis). A

grid of 100 uniformly-distributed sampling points was

superimposed on each plot, with 10 points per subplot.

Systematic sampling is preferable to random sampling when the

objective is to distinguish pattern or variability in the

vegetation (Greig-Smith 1964, Gauch 1982).

Trees and shrubs were sampled by use of the point-

centered quarter technique (Cottam and Curtis 1956). The

nearest tree and shrub in each of 4 quarter-circles around

each sampling point was recorded by species and distance from

the point. Trees (woody stems >5 m in height) were separated

into dbh categories (<10, >10-30, >30-50, >50-70, and >70

cm). Shrubs were defined as woody stems 0.3-5m in height.

The number of shrub stems was recorded in each quarter circle

within a 2-m radius from each sampling point for determina-

tion of mean shrub density. A coefficient of variation (CV)

was calculated for distances to nearest trees, shrubs, and

trees and shrubs combined in each subplot (Roth 1976), and

for shrub density. A mean CV for 10 subplots was equivalent

to the CV for a plot. The Shannon diversity index (H',

logl0) was calculated for trees and shrubs for each subplot

and separately for each plot. Presence or absence (+ or -)

of vegetation within a 0.5-m diameter circle centered on each

sampling point was recorded for 4 layers: herb (<0.3 m),

shrub (>0.3-5 m), understory (>5-10 m) and overstory (>10 m),

and H' was calculated for profile types (e.g., +++-, ++-+) in












each subplot and plot. Mean canopy openness (%, as

determined by a spherical densiometer over each sampling

point) and CV of canopy openness were determined for each

plot and subplot.

Canopy gaps and bayheads were mapped on each plot and

converted to proportions of area by use of a dot grid. A gap

was defined as a vertical hole in the canopy > 10 m in mean

diameter (a minimum area of 78.5 m2), and included canopy

openings caused by sinkholes as well as windthrow (treefall)

gaps. The proportionate gap area in each subplot and plot

was calculated in 3 categories: GA (gaps with shrub-sapling

growth averaging <2m in height), GB (gaps with shrub-sapling

growth >2-5 m in height) and GAB (GA + GB). The

proportionate area occupied by bayheads was calculated

separately (BAY), and added to gap area for a final patch

category (GAPBAY).

Local (edge-specific) sunshine data were collected

during censuses of east-facing edges in winter 1986 to

determine whether edges warmed by early-morning sun had

greater densities of birds. Edges were considered sunny if

sunlight was directly striking the edge face at the time of

census, and not sunny if cloudy, foggy, or before sunrise

illuminated the edge.











Data Analysis

Data were analyzed with SYSTAT programs (Wilkinson 1987)

on an IBM PC-XT. Major analyses included least squares

regression modelling (simple and multiple), analysis of

covariance (ANCOVA), tests for homogeneity and goodness of

fit, and tests for difference between means. Correlation of

bird densities from subplots between seasons was a measure of

consistency of site use and thus indicated which seasonal

combinations were homogeneous. Bird densities had normal

distributions in all seasons, as determined from normal

probability plots. Some habitat variables (DIST, HT, HS,

HPD, ST, SS) were distributed normally without

transformation; the other variables were normalized and their

variances stabilized by logarithmic (In) transformation.

Zero values for GA, GB, GAB, BAY, and GAPBAY were converted

to -10 on the log scale (smallest log-transformed non-zero

values were > -5). Zero values for bird registrations in

subplots were converted to .001 for single-species regression

analysis.

Edge effects in the 12 edge plots were determined by

analysis of registration densities in 5 zones 100 m wide

parallel to edge and 50 m perpendicular to edge, each

comprising 2 subplots (e.g., 01L and 01R in Fig. 1). A G-

test for goodness of fit (Sokal and Rohlf 1981) was used to

test the extrinsic null hypothesis that bird registrations

were distributed uniformly in the 5 distance zones, Ho:











Pi = P2 = P3 = P4 = P5- Overall G-tests for plots (all
species, all seasons), seasons (all species, all plots), and

species (all plots, all seasons) were partitioned into

separate G-tests to determine which individual distance zones

were significantly high or low in density relative to the

mean (expected frequency). G-tests also were performed to

test for uniformity of density in distance zones in the 3

interior plots.

Regression analysis was used to model response of bird

density to distance from edge (DIST) and to habitat

heterogeneity variables. Dependent variables were

registration densities of individual bird species and all-

species sums, totaled for each of the 4 seasons, for all

seasons combined, and for appropriate combinations of

seasons. Independent variables were distance from edge and

habitat heterogeneity variables (Table 2).

ANCOVA was used to test regression models for

differences in bird density among groups, e.g., between east

and non-east facing edges, between high- and moderate-

contrast edges, and between subplots with and without

gaps/bayheads, in response to the independent variable

(covariate) DIST. A preliminary ANCOVA model was first

applied to test for homogeneity of slopes among groups. If

slopes were homogeneous, ANCOVA was used to test for

homogeneity of Y-intercepts among groups (equivalent to a

test for homogeneity among group means, Sokal and Rohlf









19

1981). The null hypothesis of equal density of birds in edge

and interior plots was tested by comparing the mean number of

registrations per subplot in each group in winter and spring

1986, when all 15 plots were censused.

Simple linear regressions were performed for all-

species registrations in each season and in all seasons

combined for each habitat variable. Multiple regression

models were constructed using all possible subsets

(combinations) of variables. Criteria for optimal (i.e.,

best prediction) regression models were (1) the highest r2

value; (2) the fewest number of independent variables, each

with non-significant correlations (P > .05) with all others;

(3) each variable with a significant (P < .05) t-statistic

for regression; (4) homogeneous slopes among groups (e.g.,

individual plots), as indicated by P > .05 for group by

covariate interaction; (5) normal distribution of residuals;

and (6) homogeneity of variance of residuals across different

levels of independent variables, as indicated by a

homoscedastic plot of residuals against estimates (Sokal and

Rohlf 1981, Gutzwiller and Anderson 1987, Wilkinson 1987,

K.M. Portier, personal communication). Analysis of residuals

included correlating residuals with each independent

(habitat) variable not in the optimal model. Finally,

correlations with habitat variables were determined

individually for the 12 most abundant species observed during

winter-spring 1986 in all 15 plots.
















RESULTS


Habitat Description

Canopy gaps caused by treefall and sinkholes were a

prominent feature of most plots (Table 3). A mean of 3.4% of

plot area was occupied by canopy gaps (> 78.5 m2). Sinkhole

gaps were prominent in plots PP1, OF1 (an outlier in gap

area, with one canopy opening of 3208.02 m2), and IF1.

Treefall gaps averaged 3.1% of plot area; the largest single

treefall gap (in SA1) was 864.66 m2. Bayhead vegetation

occurred in only 2 plots, PP2 and IF1, where it occupied

18.3% and 9.8% of plot area, respectively. Ninety-one (61%)

of the 150 total subplots had gaps and/or bayheads, which

covered 5.3% of the total plot area.

None of the habitat heterogeneity variables (Table 3)

was related significantly to distance from edge. The

strongest association was a positive correlation between tree

species diversity (HT) and distance from edge (r = .163, P =

.075). Plots were rich in tree species, ranging from 17 to

27 (x = 22.33) and in "shrubs" (which included tree saplings

in the shrub layer), ranging from 24 to 39 species (x =

29.73) (Appendix I).










TABLE 3. Summary of habitat measurements from 15, 5.0-ha
plots (see Table 2 for definition of variables), San
Felasco Hammock, Florida, 1986. HT, HS, HPD, LG, ST, and
SS are measured at the 5.0-ha scale; other values are means
from the 10, 0.5-ha subplots in each plot.


Plot VT


VS


VTS


DENS


VSD


OPEN


PL1 55.8 68.9 87.1 6.8 62.9 5.6

PL2 56.8 75.2 96.3 13.8 71.6 7.9

PL3 58.1 75.2 95.9 11.2 67.9 9.2

PL4 57.8 74.0 88.5 8.7 103.9 8.6

MA1 59.0 76.3 91.1 8.7 92.7 6.3

MA2 58.0 80.6 90.4 7.8 86.9 6.1

SA1 58.2 71.5 93.5 9.4 80.4 5.6

SA2 55.6 90.4 88.2 9.0 91.2 6.2

PP1 58.3 83.1 101.8 12.0 60.5 5.9

PP2 56.8 67.3 100.3 12.6 61.7 5.3

OF1 68.5 87.9 109.0 10.2 70.2 12.4

OF2 56.0 77.4 93.4 10.9 68.1 4.9

IF1 59.9 74.0 99.0 15.2 71.3 5.3

IF2 56.1 61.0 87.4 7.8 83.5 5.9

IF3 57.3 80.9 89.3 9.1 93.3 5.6

x 58.1 76.2 94.1 10.2 77.7 6.7

SD 3.1 7.7 6.3 2.4 13.5 2.0










TABLE 3--continued


Plot VCO HT HS HPD GA GB

PL1 57.2 1.15 1.15 .66 .010 .003

PL2 37.2 0.97 0.93 .61 .005 .030

PL3 44.2 0.91 0.87 .52 0.0 .060

PL4 37.8 0.99 1.17 .39 .008 .032

MA1 57.7 1.08 1.17 .52 .004 .048

MA2 53.8 1.07 1.15 .69 .005 .048

SAl 48.2 1.02 1.16 .54 .005 .037

SA2 61.9 1.04 0.98 .59 .010 .008

PP1 51.5 1.02 0.88 .45 .022 .009

PP2 43.0 1.00 1.04 .47 .005 .002

OF1 67.3 1.10 1.14 .62 .068 .010

OF2 35.8 1.05 1.08 .50 0.0 .003

IF1 48.5 1.20 1.21 .48 .020 .004

IF2 50.4 1.00 1.17 .56 .010 .030

IF3 40.1 1.10 1.35 .60 0.0 .008

x 49.0 1.05 1.10 .55 .011 .022

SD 9.5 .07 .13 .08 .174 .020










TABLE 3--continued


Plot GAB BAY GAPBAY LG (m2) ST SS

PL1 .013 0.0 .013 500.00 25 33

PL2 .035 0.0 .035 319.55 19 26

PL3 .060 0.0 .060 620.30 17 24

PL4 .040 0.0 .040 839.60 20 30

MA1 .052 0.0 .052 651.63 25 26

MA2 .053 0.0 .053 363.41 27 31

SA1 .042 0.0 .042 864.66 23 31

SA2 .018 0.0 .018 200.50 26 26

PP1 .031 0.0 .031 914.79 22 31

PP2 .007 0.183 .190 125.31 22 28

OF1 .078 0.0 .078 3208.02 22 32

OF2 .003 0.0 .003 150.00 22 30

IF1 .024 0.098 .122 870.93 27 39

IF2 .040 0.0 .040 651.63 17 27

x .034 .019 .053 701.65 22.33 29.73

SD .022 .052 .048 746.95 3.24 3.75











Birds

One hundred twenty-nine bird species were observed on

the San Felasco Hammock study plots in 1985 and 1986

(Appendix II). Quantitative analyses were conducted on 27

species; 102 species were excluded because of insufficient

sample sizes (n < 30 for 12 edge plots over all seasons) or

sampling biases. Breeding species richness (S) was

significantly higher in 1985 than in 1986 (Table 4; t = 3.89,

P = .003). In 1986, when all plots were censused, Sidid not

differ between edge and interior plots (t = 0.681, P = .508).

For all plots combined, S was significantly related to only

one habitat variable, variation in shrub density (VSD; r =

0.517, P = .048).

Correlations of bird densities in subplots between

seasons indicated that site use was not always consistent.

For the 12 edge plots, site use in the 1985 and 1986 breeding

seasons (S85 and S86) was consistent (r = 0.56, P < .001).

Site use for edge plots in fall 1985 (F85) was not consistent

with that in any other season (P > .05). Site use for edge

plots in winter 1986 (W86) was consistent with S86 (r =

0.272, P = .003), but not with S85 (r = 0.126, P = .17).

Site use in W86 and S86 was consistent for the 3 interior

plots (r = 0.51, P = .004) and for all 15 plots combined (r =

0.30, P < .001).











TABLE 4. Breeding bird species richness in 15, 5.0-ha
plots, San Felasco Hammock, Florida, 1985-86. A species
was included only if > 25% of the territory of one
breeding pair was within plot.


Number of species

Plot 1985 1986 Mean


PL1

PL2

PL3

PL4

MA1

MA2

SA1

SA2

PP1

PP2

OF1

OF2

IF1

IF2

IF3

x


16.25


14

16

15

17

14

18

13

12

13

12

12

12

16

16

15

14.33


15.0

16.5

14.5

17.5

15.0

17.5

14.5

14.5

14.5

14.0

14.5

13.5

16.0

16.0

15.0

15.23


a Not censused in 1985











Edge Effects

G-tests of the null hypothesis that bird density was

uniform with respect to distance from edge, in the 12 edge

plots, yielded diverse results (Table 5). For all seasons

combined, 6 of the 12 edge plots had a significant

concentration of bird registrations within 50 m from edge; 4

of these 6 plots also had reduced density in the 2 zones

farthest from edge (150-200 m and 200-250 m). Of the 6 plots

that did not show a positive edge effect, 3 exhibited a low

density at 200-250 m, 1 a low density at 50-100 m, 1 a high

density at 150-200 m, and 1 a low density at 0-50 m and a

high density at 100-150 m.

For all 12 edge plots combined, a positive edge effect

was evident for all seasons combined, for the 1985 and 1986

breeding seasons, and for winter 1986--but not for fall 1985

(Table 5). Although the density of registrations in the 0-50

m zone for fall 1985 was not significantly high, densities in

the 2 zones farthest from edge were low. In all other

seasons, densities in the 0-50 m zone were significantly

high, indicating an edge effect, and those in the 200-250 m

zone were low.

Bird densities in none of the 3 interior plots were

higher in the 0-50 m zone; hence, no "pseudo-edge effect" was

evident (Table 6). Although 1 interior plot had low density

in the 200-250 m zone, the other 2 had high densities in the

central zones (significant in one case). Densities in all 3


























r-I
,-4


*H 0 0



0) 1


,Q to
4 00 I


o co4
w0 w 00
4.-
(0 -9
V 4) 0)a 0n
En r -H (1
4) 0 k4 4)
4) N O
I H
U 0) ( *

V 'U

'oin o Q
)-,4 1

UIn i i
)0 0 C



S-H ) 0
CO

in um






44 ,9 0 (0
4 0- Q)
*.4 0 in
3 0 *4J
v -1q 0 4)
0-4 r-4
01 in rr-4
-1 c l -


4Jo
MU r4l

* P (0 0) *
k nI H +rd
M 0 4.) 0
EQ un
a^


>01
*U 4-1
-H t71 (1)
.in4 r4
M M
P4


>4 z z >4 >4 Z Z >4 Z >4


n a
H I


1 r-1H
rHl (N |


% aN

al (O ril N N


H N m H NHC -l M ( N0
a4l 134 l04 D4l Mf 0f a4i rt4 0 0


NI LO M o NM (n V 0 nl
col o m n m k < 0 0 q|
H r- i- Hil H t-4 i-I r-I Hi i-4 r-l



























0*
$ X


>4 >4 >4


co o m -:r
r-i| V-i| VIr 'V
C-4


r- co co i
N Io co o i
H- M N !
r-l


0) 4-1
> Q) 0
-4 ts 0)
4-1) f 4-4
*rl 441
U)
0
04


0
) 0
C 0
0
*>

0


*H


*ro 0 41

,4 4
0>

40



0-4


u 0 0
C



cn 00)


4 O
II r- 4

a 030











0 z 9

(4-4 0)0)
*1-4 *4
Or >C I









CM*)
1I t c


I C 0)


a .Q$.
0 C C I









E O


<
H
I 0
co 41
in

H >
0
0)



0 -
.



0
0>
LA 0

I > C
H p H L
o *-H



W 0 0
4-'> 4.J S
I 0

.H 4-w 0
(0 :1 :
C)0 0

*4 OH>
*H U r
4f- 4-4 *H(40-

C Cl
0 *'-c I
> 4
01 0


41 .0 C

0C XI O


W) 0C



CO 40
H > C
.1-4
a o


a)
0
00)






0
OJ Q)
(0U
*- 0

0
L o

c. -
LO


-40)
I:*




0
4.

r-1 U







r.)'




H 0
I








0










S0
IUC








<- l

CO

SC



0 0
0
sat





























0 O
* o
A
V



0 LA
* *









r4


U00
car



-40 C

(0 0M
c*



M O

(0 0.




40 W
Q) W 9





C 0


SOW
O 0

'0 0
) C (0

S0 (0

00 (0
a c

ON m

U4 0)





140 0
O o



N'-
C4) =







%0





E-4
*I-l I






v> u i



pj C 0
OQ 1


M m 11 0
in o o co0
1-4











co r% '-I





co 0 LA m
ID0 in %0
V-4
a ua v e


EOOV)


0
O
0

41
0




LO
-l


u





0
0

co
CO



41
a





I
-(



0
a
0

Srq



0)

4-1






0




> -4
* 3
M


I
0






-4
0


to
0



0
0








4-co




0

4 1

3 I
-4o
LO
0
Uo

0)


-4..


4 0
(0
m>-i






-4
0 r.


044
C IN
-I 0
A3 i

u











interior plots combined were highest in the 50-100 m and 100-

150 m zones.

Individual species responded differently to edge but

were classified into 3 general categories (Table 7). Twelve

species were edge-attracted (i.e., they showed a significant

concentration in the first distance zone), 11 species were

edge-indifferent (i.e., they had neither higher nor lower

than expected densities near edge), and 4 species were edge-

avoiding (i.e., they showed lower than expected densities

near edge). All 4 edge-avoiding species and 10 of the 12

edge-attracted species (exceptions were the Ruby-crowned

Kinglet and Gray Catbird) bred on the study plots. In

contrast, 7 of the 11 indifferent species were wintering

birds.

The directional exposure of edge plots influenced the

distribution of birds with respect to edge, but only in

winter (Fig. 2). The relationship between bird density and

distance from edge for east-facing and non-east facing edge

plots, in the breeding seasons, did not differ in slope (Fig.

2, A and D; F = 0.242, P = .623), or in intercept (ANCOVA, F

= 1.275, P = .261). Regressions for fall (Fig. 2, B and E)

also did not differ in slope (F = 0.919, P = .340) or in

intercept (ANCOVA, F = 0.003, P = .958). In winter, however,

the slope for east-facing edges was significantly steeper

than for non-east-facing edges (Fig. 2, C and F; F = 6.723, P

= .011). Total winter registrations in subplots averaged





















-I
Ul 0)
4) t 4.

M4J *~.,-4




'44V'44 0 >
ao I w u
0 r 0
4t-4 rO 44 0 3
0) *q-
U -4 UW 0


(n 4) u ) >
v -P kQ) 4-)

0 0) -o
o o 4 -4


00 0 tr
4) ail > .iq

a) CO w m
b) I CP r.
)00 )
sid V co V -'-
.Q 0( k-i
CO O 4
3 (Ua -v


-H W3 0 $4 3
tH O >




0 -r4 (a

C (* (U &
o o NA
oe o>








0 ( 0 w)V
0 r-14) u
40-





W 4J 4J U)
0 0 CO 4-) -1
#>0 N
CO0I0
cr 11 e




ak Q)Z
mao9 o
04#* SN


0 001 0


[r- C4
r o 0








N .4 CM









NI .' (


S I v %D co lrI
Oil Ni N CN HI H i


u
M 0
Pc r-P 4
A ( 0
(0 0 C 0) 4

3: 4- TI a aM
Q H 4 0 4) V- 4-
PI V ". 0
&40 $i 0 0 04 > a)

W 4 0 4 4- 4 I U
0 ( 2 M44 U 4 V v C C
S(U E- c > r o 0
5 l C G 0 HO 4)
a O ( -4 0 aI 0o 00 o S
I Z A H Z Z IH X
M 4. 0 +. 4.) 4. IV >ib' 0
u '4-4 5 -4H VO AC 0
Q 0 10 0 0 3 00 3-H 3
M Z u E Z s 1s MM C


r-l
.4


00
H-1

o o
























H H
0 0
V V


H H
* *l


chi 'O


c NM


N v (1S









COI NJ


41

S.'
0)
H




0)
Pc


0| co o col r| ml col
SCl r-i HI





IO0 %D q M N n LO





'0D W.0 H 0 cO r-1l c
IO Cl l m r-Ai





N C CO In I ) H- co L
i m w inL m mn 04 M


0 '0
%1





P4 0


ro m
O O





O -4
S0



C Ha)
:3 HM


m cO c o0 0
V) a a a aC


0

M, 4 41
00 0




0 0'0
UI HO 5
C~ P1


'0




IQ
01
H
H)

S4W

>0


C


*O
4,









E-I
H























r-4 r-4
0 to 0 0 0 0 r-
f H 0 H- 0 0 0 0
1
A A A V V V V C
0

0

i- o
NN HM 1 HL o0




0 1 '4-i

4 0
N -q





-H 0 N U 0 r 01 CO
44 cN H H N N n w rq>
) I N H- Q 0
0 0 Om


C A o N N 01 ul LO 0t
o H H H H4 m LA LO HI
N I IN H

cot t
> 0 %0>


0 0


C O -4
-o t H N > %




H 4 H O-


4a u $4 in C4
0) 0IA H1 HA LA





v0 00 C


o q > a N H p 0 iu




0 4 0 H ) A 0 H P4
r 4 4 (. 1 > P r- o Ir_
00 C C.4 -










4 0 .0 to
40 H 0) H -,I






U 4 4 U w I v v v
( ) I 0 co 0 54 4.
4 U H0 0 0 0 r-l
o H 0 M I W r- 3 I >
4 0 H *l 1 0 0) M I ) r>l -HH
C 0 5- 1 ia >1 V> 0) E- CO t zr 4-4

H U 4.)I 4.i a F Ia V' U

I C.4 ( C I 0 5O CD V 0 + 0
0) i H4 c l a) 0 U 0 -rH
E -4 jC 0) CI ) I ) 0 c4 In
rI en 2 M 3 CQ s: M s s ui























* N*


CfI

x




0
rl4

0CN
O II



II

>>


* N *















***ca


N NqC (0N **


00 0


0 0 0 0 0
0 CO ( C\j


suo!JDj si6e 9


o* c C c p


0* m *


E

e--





E
o
LO






-u-
C)


C 4-j
0U 0 C
.^ CO .v-




E C 0w 41
*.10 *.r
a) a)
0 CO u
P 4-J V 0W)
4-4 0 -

00
Co bo 4-1 C
41 1U 0 4-I
M U *rl
O r0-4 u

C cU
.C *r4 M4
4W U Co
*r a Q) C
S4-4 a)

C Co *r4
0 (0 u Z
*r4 cm
4J 4


Co CO *

CL o I -I
aU C C m
P 0 0 4-4
mcZ
CO
p-4 a) .- 0C
*,4 CO 9Q 4-
.0 '-0
W -4
4.4 C Q.
0 *-r H
c W 41 ba
0 4) C V
*r- r-4 )

13 M

S000 -l
41 0 0 ..CO
V V .

0 0 WC
C14 (U- a)
CU C
C C C


'4- 41


* N 0 1 m











0


o


0-
-- : o 0 rJl r-

II
o .1 0


0 o C\






C'- -
o L
C.. E





S* -N r E
W 0
l0 U



U)




U-O
P i'-- 1

00
O o


400 -


00 0
o __





ro e *
o









I I I 2I I- 0
O O O O O G
4-1

0
suo!,oDlsSi60 S


CM


c4













0
LO
c\J


r--l ON c
0



n O
C> 34 0 *
0m. /.C\J





CO4
i CU)
03 0 O c>



a E
I-
u- -.
0
U,




S / 0 .\
C-,
0) 0 c


qq- I- 4-
cc









o 0
SS N












0
P-4




4-
Fr) CU 0
S UQI4.D~libed


suo!~ois!~a(


'-4














LC

10
O o o oJCl 0
CII


00

+- 0)









0 0 0
0 c
II ro E




O I

ci-



00 %J c






















0
S suo0 o qe
cnI






















C14

o



I-4
0L I
QQ C
/- 0











c
0






1-
H













0
O






x 0



0)
o -E






1 0







00
C 0 03
c o 1 I

LL


















LJ






0 ) 0 0 0 l0 C0
a
I 1 -0
































C-
Lr 0


Io


















c
rr> ~U
1-1
~O ~h. M (













0
O



(/) cuj o
oor
O: 0
" 0
x O


o o)

o o r
ID o o to N


i o aN 0II

0 c


I- e L*






a)I



ClC













0
SUo IS 8

C4 a
C *-

L-














cc



i











10.15 (SD = 6.61) in east-facing plots and 5.15 (SD = 4.21)

in non-east facing plots. The difference in means was

significant (t = 4.942, P < .001), indicating that birds used

east-facing edge plots more than they used non-east facing

edge plots in winter.

Sunlight (and presumably a warmer microclimate for birds

and their insect prey) apparently attracted birds to east-

facing edges in winter. Of 36 "edge-mornings" (each of the 6

east-facing edge plots was censused 6 times in winter), 16

were sunny and 20 were not. The mean number of registrations

in the first distance zone (0-50 m from edge) was 3 times

higher on sunny mornings (x = 9.94, SD = 5.20) than on

non-sunny mornings (x = 3.60, SD = 2.42), a significant

difference (t = 4.851, P <.001).

All of the edge-types sampled in this study were abrupt

edges between mesic hammock and relatively open habitat. Of

the 2 natural edge-types sampled, however, the marsh edge

(MA1 and MA2) had higher structural contrast with hammock

than did the sandhill edge (SA1 and SA2). Each of these

edge-types was represented by 1 east-facing and 1 non-east

facing plot. In the breeding seasons, the slopes for high-

contrast marsh edges and moderate-contrast sandhill edges

were significantly different, the former being positive and

the latter negative (Fig. 3; F = 13.463, P = .001). Neither

slopes nor intercepts were different between these 2 edge-

types in fall or winter (P > .05).











41
0
LO


4..J
O (o




(0 0
4o 0
- E o sc


0 0 0, C





0) CO O4
0 0 o
o -o4




L_0 0
I I I, t 1- r
CO | 1- CCO i:l


U) 0 .C-



4- 4-

4-- "
O 0 0
L.O



< M
0 0 ) 0) 4)
C- 0 co (D 44J
mC *'- 4 C












So


V
04J



oI to
." 01 / -0

















Pc
02
















E c>










42
0



OC\j


(D T3 r
00 J 0 0
00

O
SE+ *
OEm






OE ** o E
OD 0



a,
C

* O
a 0



0


D 10
0
0 O \. 1 .




o --- 0 -- 0 -- 0 -- 1 --0 0 -- 1 0 QJ










Bird Densities in Edge versus Interior Plots

Birds generally were attracted to edge within edge

plots, although seasonal trends and variation among species

and edge-types were evident. Edge effect was not apparent,

however, when bird densities were compared between edge and

interior plots (> 700 m from edge). Mean densities in

subplots of edge and interior plots were almost identical in

the seasons when all plots were censused (Table 8).

Variation in density was greater among subplots of edge plots

than among subplots of interior plots. Thus, edge affected

the distribution of bird activity within plots (and within

territories) that abutted edge; between plots, there was no

apparent attraction of birds to parts of the forest near edge

as opposed to deep in the interior.



Internal Patchiness and Its Relation to Bird
Densities and Edge Effects
Internal patchiness supplemented distance from edge as a

predictor of bird density in edge plots, but was a more

important predictor in interior plots. Correlations of bird

density with distance and with habitat variables varied among

plots and seasons in strength and, in a few cases, direction

(Table 9). Distance from edge (DIST), variation in distance

to nearest shrub (VS), shrub density (DENS), canopy openness

(OPEN), shrub species diversity (HS), and proportion of plot

area in gaps and bayheads (GAPBAY) were the variables with

the largest numbers of significant correlations with bird










44
TABLE 8. Number of bird registrations in 0.5-ha subplots of
5.0-ha edge and interior plots during the seasons when all
plots were censused, San Felasco Hammock, Florida, 1986.
N is the number of subplots in each group (edge and
interior plots).


Seasons/Registrations Edgee Interior z P


Winter 1986

N

Range

x

SD

Spring 1986

N

Range

x

SD

TOTAL

N

Range

x

SD


120


0 30

7.65


6.06


120


3 62

25.33


9.84


120


7 69

32.98


12.88


30

2 15


7.10

3.47


.65


.52*


30

11 46


25.00

9.04


.18


.86


30

17 61


32.10

11.20


.37


.71


P-value is for 2-tailed z-test. Group variances were
homogeneous for Spring 1986 and TOTAL, as determined by
Bartlett's test, but not for Winter 1986.











TABLE 9. Significant correlations of bird registrations in
subplots with distance from edge and habitat variables for
15, 5.0-ha plots in each season, San Felasco Hammock,
Florida, 1985-86. Variables that produced no significant
correlations (HPD, GA, and BAY) are omitted.


PLOT DIST VT VS VTS


F85:-.949***
TOT:-.709*



S86:-.859**


F85:.686*


S86:.703*

S85:.724*
S86:.721*
TOT:.765*


S85:-.667*
S86:-.728*
TOT:-.721*

W86:-.858**
S86:-.634*
TOT:-.794**

F85:-.786**

W86:-.655*


PP1 F85:-.840**
TOT:-.716*


PP2

OF1

OF2


IF1


IF2


IF3


F85:.740*
S86:.763*
TOT:.657*


W86:-.817**

S85:-.774**

S85:-.816**
TOT:-.734*


W86:.746*
TOT:.741*


S86:.759*
TOT:.729*


PL1


PL2

PL3

PL4


MA1


MA2


SA1

SA2











TABLE 9--continued


PLOT DENS VSD OPEN VCO


F85:-.695*
W86:-.695*


S85:.828**
TOT:.828**


S85:-.862
TOT:-.715


S86:-.636*


W86:.696*
TOT: .654*


PL1

PL2


PL3


PL4

MA1


MA2

SA1

SA2

PP1

PP2


OF1

OF2

IF1



IF2

IF3


F85:.644*


S85:.740*


S85:.698*


S85:-.709*


S86:.676*

S86:.730*
TOT: .681*


W86:.661*


W86:.765*
S86: .798**
TOT: .893***


W86:.742*


S86:.674*
TOT: .670*


W86:.857**











TABLE 9--continued


PLOT HT HS GB


S85:-.878**


F85:.768*

S85:.952**
TOT:.819*


PL1

PL2

PL3

PL4


MA1

MA2

SA1

SA2


S85:-.861**
TOT:-.796**





S86:-.719*
TOT:-.704*


W86:.915*


W86:-.655


W86:-.721
TOT:-.728


S85:.706*
S86:.880**
TOT:.751*


PP1

PP2


OF1

OF2

IF1


IF2

IF3









48

TABLE 9--continued


PLOT GAB GAPBAY

PL1

PL2

PL3 F85:.768* F85:.768*

PL4 S85:.959*** S85:.959***
TOT:.819** TOT:.819**

MA1

MA2

SA1

SA2

PP1 S86:.972*** S86:.972***

PP2 S85:.823**

OF1

OF2

IF1 S86:.850**
TOT:.947***
IF2

IF3


* P < .05

** P< .01

*** P < .001











registration density. Multiple regression models explained

5-71% of the variation in bird density within edge plots,

interior plots, and all plots combined (Table 10).

GAPBAY, the proportion of subplot area in gaps/bayheads,

was the single most important variable in multiple

regressions, although other variables were more important in

some seasons; DIST and HS were the most important variables

in subplots that lacked gaps or bayheads (-G). For those

subplots that contained gaps and/or bayheads (+G), GAPBAY

explained 14% of the variation in bird density in winter and

spring 1986 in all plots combined (Fig. 4). Bird density in

gap/bayhead subplots was significantly higher than in

subplots without gaps/bayheads in spring (P <.001), and in

winter and spring combined (P <.001), but did not differ in

winter (P = .26) (Table 11). Gap area alone (GAB) was nearly

as good a predictor of bird density in all cases, but does

not appear in the optimal equations (Table 10) because it was

highly correlated with GAPBAY (e.g., r = .88, P <.001 for all

plots combined); in fact, GAB is equivalent to GAPBAY in all

but the 2 plots (PP2 and IF1) that contained bayheads.

Bayheads, however, were major attractors of birds in these 2

plots.

Distance from edge (DIST) was the most important

variable in fall and winter in the 12 edge plots, and in the

breeding seasons in subplots of edge plots that lacked

gaps/bayheads (Table 10). All correlations with DIST were




















4.-


H I ~ i) ti (
) 0-4J C 0 0 r- 0
r. co)t 0 r, Z -H (d ,-4
) Ln) -,i M(a > +I
o to o a) a(ri o





*- M 0 M 0 04 M 0) I + I + + + + + + +

Jtr a) 'i 4 or
C *-I ,0 ) E -40
, to H %-m U) + .
-4i t OH la) o o r-0
J > 4'U-(0 0 0 0 0 0 0
HHH00 \ *WW O. O V V

40 +JCO H 0 CO O -C
in k e os ai o N I ++ O + +i
-40H -40 H- 0 i 0
0 (0 ) -C 00

C' ( O-V I> r.0A 9 o4
O H 041> r- i- i -- -0 O-
S.,n O ou Q*- 0 o o
o o' M a O a >i .
n O (*n Oi E -P O O -, ,- *< I VI
m 4004c I4 W -E-4






04 0 0 0* 0 -



0 u o oo 0- -0
, (X H p o H
v I I r. r- o U co o Q 4 r





*HJ HrI r( rO M^ m-l H H^ OU)- c- N
9 -H 0 (13*-H 14-4 H 00










043 (04-J 4JP ( 0- C0 % l 0O H 0 0 0-
3 t-o'04.) 0i-H>4-) En +Q + E
UO 0 V to AS (0 >4 >




0i OM 4 O4-) 0 l '- I I I I




SJ N4J 00-. M )i O m
iH (0 6 C 3 l4-).-i c(O HlO uO H( C- n
* w .- O 0 OH *r *4 M y in o
0) to 06> :00 p 0 o





(03o04 J o I0-H0 CO I 0 04 (k (
W 4) r. FA OD :J eU-4 -
4) H! Q -C p04 ((d ( H H H
pn )o a coO
-HM 4 r-i O M+ P N N Nr +
W >4 4- W 0- (1) U ) H












rzl w^l CA Ca' U COH + I H +
0 r-A O1 A- +0 4+

j Vo 0 (U Bo M to v O Kr Ch
(13 0 ; 4 1 c4 *




*-iOrO0-)0H0 0 t 0 L A L
0 0 0 M 4-) C0





























>4

En wc z
E-4H E- E-4
> >0 >
++ ++ I I


0 0
EnE-i p )t U M
> > >+ >+
I + + 1 +


z z
w 0 0

0> >> > 0
++ 1 + ++


>4
>4






*O c> t

LA +H

00
iLO H


in + cc





I i-4 + 0
SCO
z 0
H r 4

H E-


m P.
>4



* 0


+ + I,

0 Mu ar
C!J 1a






* C (NJ
1H H -


H H
(0) (0
H H
Q 0
m M o
occ 0
. a
IcO I
0

* H
CO I r
cO1 i-l


WH

IV

ON









u






























0 0 0
En C MO C I
+ > >
+ +1 +1


0 0 i 0 0
++ +E U+
+ + +1 + +


Z W
rp aIm c A
> > > > 0 Q
++ 1+ +


S m>4



qw H

Lo >L L



.I hI ()
*lu .
co +In


co
M1


a ,
>4 >4




CV~I
H LO




+0 +
oH co


HI H






n- +

E-4
*- 0
4 E-1


0
r9
*r1
4J












0
U)
a
V


40


0
C
E-1

c
o
I
o

rE


































M E-4 MW





o o
o o



S CO









L*











+0 +
. *






01 co +

+ I
n\ nC


** *
0t Uo


0
-1 0
iO 0
o
* V
v
v
v C4

SQ4
4* *



C3o
vU2C

++


Hl
0
0

v


4

0
0
4






+

01

H
C',
o





o


a)
-o

0
E3



I

0
I


a)
rt

E-4


%0
cO
W1

















O
S 0 O
X u ur T

S0)
N C CQ)

\* *
S* 0 ,I
CO


o( il ~l .T3

II r- a




c' a cO
I *



*M O
,
0. cc 0

No CD 0
0 I C r
m 60
(M* \ r I c 1

N N N4N *n

0 r-
m 0










* N 0 r- i-4 cO
0CM N CO .,

p 0 0
"a 0 p



SC 4CM




0)W
C* in 0\0 0 M 0 V


\n aof. U U)



o Oa > *
0C0 44 0- 00









S6D m ro m o-

0 r. a

.1-4 *mU
\o -a

S .0 .*0
P Q91 'a
\t C >
\r- -m X 0C
0ul 0I 0 0 00 m E-4







*0 =!
U') U4












TABLE 11. Number of bird registrations in subplots with
(+G) and without (-G) area in gaps/bayheads for the 15,
5.0-ha plots, winter and spring 1986, San Felasco Hammock,
Florida. N is the number of subplots in each group. P-
value is for 2-tailed z-test.

with without
Seasons/Registrations caps gaps z P


Winter 1986

N

Range

x

SD

Spring 1986

N

Range

x

SD


0 25

7.96


5.54


6 62

27.88


9.73


59

0 30


6.90

5.76


59

3 39

21.24


1.12


4.52


.26


<.001


8.09


TOTAL


11 69 7 55


Range

x


35.84


28.14


4.01


<.001


12.85 10.52











negative, indicating a positive edge effect. DIST was not

important when interior plots (calculated as DIST = 700 m for

all subplots) were considered with edge plots. HS was more

important than DIST or GAPBAY in winter for subplots lacking

gaps/bayheads, and was a significant variable in interior

plots and in all plots combined. HS was negatively related

to bird density, probably because the dense shrub-level

vegetation that was used heavily by birds often was dominated

by just 1 or 2 woody species.

Regression analyses revealed that subplots without gaps

or bayheads (Fig. 5A) exhibited a stronger edge effect than

those with gaps/bayheads (Fig. 5B), in the breeding seasons.

The slopes of these 2 regressions did not differ (F = 1.241,

P = .268), but their intercepts did (ANCOVA, F = 18.381, P

< .001). The same was true when subplots with and without

gaps alone were compared, but the intercepts differed less

than in the comparison with bayheads included (ANCOVA, F =

10.527, P = .002). There were no differences in slope or

intercept in either case in fall or winter (ANCOVA, P > .25).



Patterns at the Between-Plot Scale

Relationships between bird density and habitat

heterogeneity at a between-plot observation scale (Table 12)

were different from those determined at a within-plot scale

and were less often significant. For spring 1985 and both























*C
00
0

0



00
oto *

II
CM)





*N* N



















NO ** *


0 0 0
CO (D I-



suoipji~sibey


NO



















ON0 0









COM *
M


E


Cv

LU

E
0
+-




4-
Un


c
0 0)




o.0 c
a 0- CO
00c0 o





0)e
w w 00
W E






0 co

1.0 C 00



O CO
M0 C
C 1-4 0 r-4
0.-^



0)CO O

Q) cc* c
4-4 co
4-41 w CO C
w) < ow 0
'-' 0 Co





0 m a

o E (U
W)E p
C 0 C a
.C 44 .-r W)
co u wu


0 0 r4
C0 CO .
.- C CQ


C o0 0rl






C1 r4 C ^

t 0 CO4
CO ca V C
CU)l 00 CU






S0 '



C W0 Co


'clO k











0
N


**C CQ to
X Lr L, "
'-
0 II II




+ 0 o CU ~,p
o 0
-0




O
0 o



N O* ** E
00

0 0 0
>1 00
*- s0l 0


--C
0 ON
0







0* C\I Y~ N1e
SLO







0 -0
0 o 0 0 0 0

4-1

s uo ID pip E 0






) *4






















Ut
U 0


C r- c ( 0
00 My 0 41 M mM ME4
*HF- MH* ri = > c En
(L ) tYr- A> -u + + II +
S0 X 0

*n rc a a0 c()
0e1 01 ( 4-q 10
>i0 rH k U Q) U]

M -4 (0 N
C ) r-4 CDH M W0 0 0 0
So (amr C(O *
U 0 -4 > (0 +

SV ) q m to




O* 0m .D t -




H -0H M W d n v
ON 0 4) O




cO 0 l *
Oi QH) ( N <
c i 0c o M -o
4) 0 0 0 04








OW* C -4 0
S) Ico 44. 0 + I4

v
0 M* o WC r H Hc4)p H4 (N
04 V m*- O 0 U
S0 H 4 *H q *
0 o M r. C 0
<4) 00 0 H




4O0 4 4 0 0 0



-riHWO) H 4nV -H 0 V 1 H
w c cO co 9 0 9 o H w (




-H 4aJo -H J-n4J
$4 (3 (4p 00 u 4 o (1)0o *v
$4 > r--1 Q P rQ) M r4






tH a0f 0 -H0 U) N
0M o l n -4 o ) o
k r-- 4 4 int U
0 4)) UN0 0 0H




E0 a) P M) U) *t 0
E-4 rn u) 44


0 r Ea
IO G)M 0 0
4 U)O a a c G oIC










springs (breeding seasons) combined, tree species diversity

(HT) explained most of the variation in bird density among

plots, the relationship being inverse. In fall, a positive

relationship with canopy openness (OPEN) was most important.

Gap and bayhead area (GAPBAY) and other variables indicating

patchiness were not important at the between-plot scale

(except, as noted above, breeding species richness was

significantly associated with variation in shrub density,

VSD).



Responses of Individual Species to Habitat Heterogeneity

Responses of the 12 most abundant bird species to

distance and habitat variables revealed that, for most

species, density was associated significantly with habitat

patchiness (Table 13). Edge effects observed within edge

plots (Table 7) for many species were swamped by high

abundances in interior plots >700 m from edge; distance from

edge was an important variable for only the Red-bellied

Woodpecker (which was attracted to edge) and Hooded Warbler

(which avoided edge) when all 15 plots were considered (Table

13).

Gap and/or gap/bayhead area (GB, GAB, or GAPBAY) showed

significant correlations with density for 5 species (Northern

Parula, Carolina Wren, White-eyed Vireo, Hooded Warbler, and

Downy Woodpecker). Variations in spacing of trees and/or

shrubs (VT, VS, or VTS) correlated positively with density










TABLE 13. Responses of individual species to edge and
habitat heterogeneity, as indicated by significant
correlations for the 12 most abundant bird species in
the 12 edge and 3 interior 5.0-ha plots combined, San
Felasco Hammock, Florida, 1986.


Species Variable r


Northern Parula

Red-eyed Vireo

Carolina Wren


Tufted Titmouse

Northern Cardinal

White-eyed Vireo







Red-bellied Woodpecker







Hooded Warbler







Ruby-crowned Kinglet


GAPBAY

OPEN

VTS
VT
GAB
OPEN
GAPBAY


.199*

-.233**

.296***
.212**
.257*
.208*
.188*


(none significant)

(none significant)


GAPBAY
VTS
GAB
GB
DENS
VT
HS

OPEN
VS
VT
DIST
VTS
VCO
HT

GAPBAY
GB
GAB
DENS
HS
VTS
DIST

HT
HS


.377***
.308***
.350**
.344**
.247**
.215**
-.162*

.386***
.255**
.235**
-.247**
.184*
.171*
-.170*

.370***
.321**
.284**
.265**
-.232**
.217**
.192*

-.270**
-.192*


Downy Woodpecker


.359**









TABLE 13--continued


Species Variable r

Acadian Flycatcher (none significant)

Summer Tanager (none significant)


* P < .05

** P < .01

*** P < .001











for 4 species (Carolina Wren, White-eyed Vireo, Red-bellied

Woodpecker, and Hooded Warbler). Density of 4 species

(White-eyed Vireo, Red-bellied Woodpecker, and Ruby-crowned

Kinglet) was related negatively to diversity of trees and/or

shrubs (HT, HS). Two species (Carolina Wren and Red-bellied

Woodpecker) were positively associated with an open canopy

(OPEN), whereas the Red-eyed Vireo was negatively associated

with OPEN. Two species (White-eyed Vireo and Hooded Warbler)

were positively associated with shrub density (DENS), and 1

(Red-bellied Woodpecker) with variation in canopy openness

(VCO). Finally, 4 species (Tufted Titmouse, Northern

Cardinal, Acadian Flycatcher, and Summer Tanager) showed no

significant correlations with any of the variables.















DISCUSSION


Bird Responses to Forest Edge and Internal
Patchiness: A Matter of Scale?

A major objective of this study was to assess the

simultaneous and interacting effects of edge and internal

patchiness on bird habitat-use. Both forest edges and

internal patchiness (especially in the form of gaps and

bayheads) attracted high densities of birds within 5.0-ha

plots. Edge effect during the breeding season was

significantly stronger in 0.5-ha subplots lacking gaps or

bayheads than in patchy subplots. Forest edges, particularly

in fall and winter, appeared to "distract" birds from gaps

and bayheads; i.e., birds were attracted more strongly to

gaps and bayheads in interior plots (> 700 m from edge) than

in edge plots. In interior plots, patchiness was the best

predictor of bird density in all seasons, and was especially

important during the breeding season, when nesting, foraging,

and territorial display for many species were concentrated in

gaps and bayheads.

Attraction to edge was strongest seasonally in winter,

whereas attraction to gaps and bayheads was strongest during

the breeding season. East-facing and high-contrast edges

attracted higher densities of birds than did edges that faced

64











other directions or exhibited less structural contrast

between adjoining habitats. Of 27 bird species analyzed, 12

were attracted to edge, 11 were apparently indifferent, and 4

avoided edge. A common null hypothesis in edge-effect

studies is that animal densities at different distances from

edge are equivalent. In this study, bird densities across

distance zones were rarely uniform, and a clear edge effect

(concentration of registrations 0-50 m from edge) occurred in

6 of 12 edge plots, for all seasons combined.

Despite indications of attraction to edge within edge

plots, edge and interior 5.0-ha plots had equivalent

densities of birds and equivalent breeding species richness.

The lack of any difference in density between edge and

interior plots may be a consequence of habitat selection

mechanisms differing at different spatial scales (see below),

or may be related to the lower densities observed in the most

distal (200-250 m) zone of edge plots. Although sampling

problems cannot be ruled out, attraction to edge may produce

a "vacuum effect," where animal activity or density is

depressed at an intermediate distance from edge compared to

deeper forest (Bider 1968).

Similarly, although birds were attracted to gaps and

bayheads within plots, between-plot comparisons indicated

that bird density did not differ between patchy plots and

more homogeneous plots. Breeding species richness, however,

was positively associated with one indicator of habitat











patchiness at a between-plot scale, the coefficient of

variation of shrub density.

The empirical generalization that birds are abundant

near openings, discussed in the ornithological literature

since Lay (1938), was supported by this study. But this

simplistic interpretation is incomplete because it derives

from only one scale of resolution. Habitat associations of

birds differ depending on the scale at which they are

examined (Gutzwiller and Anderson 1987, Wiens et al. 1987).

The edge effect and the "patch effect" may be scale-

dependent in 2 ways: (1) birds respond to different sets of

habitat cues when selecting forests in which to settle, when

establishing territories or home ranges within forests, and

when selecting nesting, foraging, singing, and roosting sites

within territories and home ranges (Hutto 1985, Wiens 1985);

and (2) different human observation scales lead to detection

of different patterns (Allen and Starr 1982, O'Neill et al.

1986, Wiens et al. 1987).



Edge Relations

Beginning with Shelford (1913, 1927), who described an

abundance of animals at the forest margin, and Leopold

(1933), who advanced the idea that "game is a phenomenon of

edges," the attraction of wildlife to openings has been one

of the best-studied phenomena of habitat selection. Numerous

studies since Lay (1938) have documented higher bird species










richness near forest edge (Johnston 1947, Johnston and Odum

1956) and/or increased densities of birds near edge (Beecher

1942, Good and Dambach 1943, Johnston 1970, Gates and Gysel

1978). Although documentation of edge effects has been

ample, a lack of standardized methodologies and definitions

has produced some confusion. Sometimes the area of habitat

in various distance zones varies widely and is not specified;

hence, density-distance correlations can be spurious and edge

"effects" are really artifacts (Nelson et al. 1960, Harris

and McElveen 1981).

Much of the confusion in the edge literature reflects

the many ways in which edge, edge species, and edge effects

have been defined. Some studies of edge effects on birds

(e.g., Kendeigh 1944, Johnston 1947, Whitcomb et al. 1981)

have used qualitative criteria to classify species according

to their edge affinities. Typically, bird registrations are

mapped, territory boundaries are defined, and species are

classified as "forest-edge" if territories are concentrated

along forest margins, as "forest-interior" if territories are

located primarily inside forest, or sometimes as "interior-

edge" if territories are found both in edge and interior

habitat.

Other studies have used quantitative criteria to

determine the edge-interior affinities of birds. Galli et

al. (1976) defined edge width according to structural

characteristics of vegetation determined in a different study










nearby (Wales 1972). Gates and Mosher (1981) took a

"functional approach" to estimating edge width, based on

dispersion of nests of bird species associated with edge

habitat. Kroodsma (1982, 1984) mapped territories along an

edge-interior transect, and defined edge species as those

with highest densities (fractions of territories) within 60 m

of edge and/or a significant negative slope of density

against distance from edge. Strelke and Dickson (1980) and

Helle and Helle (1982) used densities of registrations within

arbitrary distance zones to determine strength of edge effect

and to classify species by edge affinities. My study was

modeled in part after those of Kroodsma (1982, 1984), Strelke

and Dickson (1980), and Helle and Helle (1982). Because edge

effects were tested among a series of replicated, well-

dispersed plots, statistical inferences could be made that

were inappropriate in previous studies.

Researchers in the eastern deciduous forest region have

often described a characteristic forest-edge avifauna (e.g.,

Kendeigh 1944, Johnston 1947, Johnston and Odum 1956, Forman

et al. 1976, Whitcomb et al. 1981). In contrast, this study

at the southern extreme of the deciduous forest biome (Braun

1950) revealed few distinct forest-edge birds. Five breeding

species, the Brown Thrasher, Common Yellowthroat, Blue

Grosbeak, Indigo Bunting, and Brown-headed Cowbird, were

confined to edges but were uncommon in the study area and

were not analyzed. The Rufous-sided Towhee, considered an











edge species in the northern studies mentioned above,

inhabits deciduous forest edges in Florida, but is more

abundant as a breeding species in pine flatwoods and

plantations (Repenning and Labisky 1985). Other breeding

species classified as forest-edge birds in many northern

studies, such as the Yellow-billed Cuckoo, White-eyed Vireo,

and Northern Cardinal, were found in San Felasco in all

distance zones but most abundantly near edge. In forest

interior, these latter species concentrated their activity in

gaps, bayheads, and other patches of dense shrub growth. The

Gray Catbird, a typical edge species that wintered at San

Felasco, was found at all distance zones but was strongly

associated with edge. Thus, almost all of the bird species

analyzed in this study used both forest interior and edge

habitat, although species differed in degree of attraction

to, or avoidance of, edge. Several species generally

associated with edge also inhabited the interior of San

Felasco Hammock, apparently due to its patchiness. This

observation leads to a question, as yet unanswered by any

study -- at what point does forest "interior" become so

patchy that it is no longer interior?

Qualitative aspects of edges may influence faunal

distribution (Harris and Smith 1978, Harris 1980, 1984,

Harris and McElveen 1981). Exposure and contrast are

potentially important qualities of edge in terms of bird

attraction. At San Felasco, a greater positive edge effect










was observed in high-contrast hammock-marsh edge plots than

in moderate-contrast hammock-sandhill edge plots during the

breeding seasons. This finding agrees with previous

conclusions that the magnitude of edge effect increases with

greater structural contrast between abutting communities

(Thomas et al. 1979, Harris and McElveen 1981, Harris 1984).

This study also documented a greater attraction of birds

to east-facing edges in winter, as compared to edges that

faced other directions. Densities of birds on east-facing

edges were significantly higher when morning sunlight was

striking the edge, suggesting thermoregulatory behavior, or

more likely, a response to increased insect activity. In

contrast, Helle and Helle (1982) found a peak in bird density

50-100 m from forest edge on Finnish islands and suggested

that avoidance of climatic extremes may keep many birds

(especially tropical migrants) away from edge in colder

climates. Carpenter (1935) found higher bird densities on

edges on the "lee" side of Illinois forests, sheltered from

prevailing winds; density differences between windward and

leeward edges were more pronounced in winter and early spring

than in late spring. In north-central Florida, winds are

multi-directional during the day but generally northerly at

night (Dohrenwend 1978), so wind should not produce

consistent differences in diurnal use of edges. Hence,

climatological effects of edge appear to influence bird











activity in many regions, but differ according to regional

and local environmental conditions.



Patchiness Relations

The edge effect, as it is usually understood, is a

response of animals to major habitat interfaces

(macroheterogeneity). Internal forest dynamics, however,

produce openings that are structurally similar to forest

edge, and might be considered forest edge at a finer scale.

In this study, the proportion of subplot area in gaps (plus

limited bayheads) was the best predictor of bird density at a

within-plot scale of analysis. The simple measure of

gap/bayhead area was more important than various

heterogeneity indices or the floristic diversity of trees and

shrubs. When data from interior plots were combined with

those from edge plots, the proportion of area in

gaps/bayheads was a far better predictor of bird density in

subplots than was distance from edge. This conclusion

applied to most individual species and to all species

combined. For the 12 edge plots, edge effect in relatively

homogeneous subplots during the breeding seasons was

significantly stronger than in subplots containing gaps

and/or bayheads. These results suggest that openings (and

other shrubby areas) of all sizes are attractive to birds,

but that the relative attractiveness of major edges and










smaller, internal patches depends on the range of distances

from edge and degrees of patchiness sampled.

The attraction of birds to gaps is just one indication

of the ecological significance of these patches. Gap

dynamics are an important regeneration and diversifying

phenomenon in many types of forest (Bray 1956, Williamson

1975, Hartshorn 1978, White 1979, Runkle 1981, 1982, 1985,

Brokaw 1985). In southern hardwood forests mesicc hammocks),

a number of co-dominant tree species coexist, apparently as

non-equilibrium populations, and respond independently to

disturbances that produce gaps in the canopy (Platt and

Herman 1986, Platt and Schwarz, in press). Rates of gap

formation by treefall and canopy degeneration have not been

measured in these forests, but might be expected to fall

within 0.5-2.0% per year, a rate described for mixed

mesophytic forests and many other forest types (Runkle

1985).

In San Felasco Hammock, sinkhole formation supplements

wind and tree death as a source of canopy gaps. Several

recent or enlarging sinkholes have resulted in treefalls and

shrub-level enhancement similar to that associated with

windthrows. Deep sinkholes are usually water-filled (at

least seasonally); the largest sinkholes form persistent

ponds with fringing marshes and/or shrub swamps. The largest

sinkhole in San Felasco Hammock covers 9.6 ha; the largest

gap occurring within the study plots was a 3208 m2 sinkhole










gap. The mean gap area (3.4%) on study plots was within the

range recorded by Runkle (1982) in 15 old-growth mesic

forests in the eastern United States. Although our gap

definitions differed (see Runkle 1982), gap area in San

Felasco Hammock appears to be typical of old-growth forests

in the eastern United States.

Unlike larger habitat discontinuities (edges), natural

gaps and other aspects of habitat patchiness were not studied

by many wildlife biologists or ornithologists until recently.

Kendeigh (1944) noted that forest interiors were sometimes

"infiltrated" by forest-edge species such as the Northern

Cardinal and Rufous-sided Towhee. These species, he wrote,

may occur "where openings or thickets have been naturally

made by trees being blown over or by other disturbance.

However, such openings are 'wounds' in the community

structure, and since they occur to such a varying extent in

different sample plots, it seems best to eliminate them

altogether" (Kendeigh 1944:96).

Recent studies have considered gaps in a more favorable

light. Birds may respond to gaps because they provide cues

indicating a concentrated food supply (cf. Hilden 1965). In

Panama, Schemske and Brokaw (1981) found more bird species in

gaps than in undisturbed forest understory, and considered

several species "treefall specialists." In Costa Rican cloud

forest, flowering and fruit production are concentrated in

treefall gaps (Linhart et al. 1987). In Illinois, Blake and










Hoppes (1986) and Martin and Karr (1986) captured more

migratory frugivores (in fall), granivore-omnivores, and

certain (especially foliage-gleaning) insectivores in gaps

than in non-gap areas of forest understory. Bird abundance

in gaps was correlated with greater food abundance,

particularly fruits and foliage. Many insects favor plants

growing in sunlight over those growing in shade, and

lepidopteran larvae may attack plants in gaps preferentially

(Wolda and Foster 1978, White 1984, Harrison 1987).

In this study, association of birds with gaps and

bayheads was strongest during the breeding seasons. Although

birds may concentrate in gaps because they are richer in

food, nest-site selection may be just as important (Morse

1985, Martin 1988). Dense shrub-level foliage within gaps

provides abundant nesting substrates for birds that nest in

this stratum; concealing cover around nests also offers

protection from nest predators (Chasko and Gates 1982). Ten

of 18 breeding bird species that were analyzed in this study

are primarily shrub-level (below 5 m) nesters, and all but 1

(Pileated Woodpecker) of the remaining species nest at either

shrub or tree level (Appendix II, Harrison 1975).

Van Horne (1983) cautioned that animal density may be a

misleading indicator of habitat quality. If surplus,

socially-subordinate individuals (e.g., young, inexperienced

birds, many of which may be non-breeders or "floaters")

collect in habitat sinks, lower-quality habitat may actually











contain a higher density of individuals. Fretwell and Lucas

(1969) predicted that individuals select patches of highest

quality first, but that as population increases, a threshold

is reached where individual fitness is maximized by selecting

lower-quality but unoccupied habitat. Without long-term,

intensive studies in gap versus non-gap sites that measure

differences in habitat occupancy and fitness over a range of

population densities, the importance of gaps to birds remains

inferential. Life history information (for most of the bird

species here), high resource levels in gaps, and attraction

of birds to gaps within plots warrant the prediction that

patchy plots will be preferred by birds until increasing

population density makes less patchy plots more advantageous

in terms of fitness.



Management Implications

Reviews of diversity concepts in wildlife management and

conservation (Samson and Knopf 1982, Noss 1983) indicate that

maximization of local habitat diversity and edge effect has

been a guiding principle. This management emphasis appears

perfectly consistent with what ecology tells us about the

dependence of organisms on disturbance, successional patches,

and habitat mosaics, and the inferred relationship between

diversity and stability (Pickett and Thompson 1978, Hansson

1979, Gilbert 1980, Karr and Freemark 1983, Pickett and White

1985, Forman and Godron 1986). But what is beneficial at a









76
local scale and for edge-adapted organisms, such as many game

species, may be deleterious at larger spatial scales and for

sensitive organisms (Faaborg 1980, Samson and Knopf 1982,

Noss 1983, Wilcove et al. 1986). Furthermore, natural

disturbances and anthropogenic disturbances may have

qualitatively different effects on wildlife, a problem that

awaits detailed study.

One common method of enhancing horizontal habitat

diversity is through the construction of "wildlife openings."

Lay (1938:256) was one of the first to advocate "the

provision of clearings with extensive margins" for songbirds.

Because the edge effect he noted was confined to the first

100 m from an opening, and because the interiors of large

clearings were depleted of wildlife, Lay recommended small

but numerous clearings. Leopold (1938:3) made similar

recommendations with regard to deer, songbirds, and

wildflowers: "The smaller and more frequent the selective

cuttings, the greater the benefit to wildlife." In practice,

wildlife openings usually have been constructed for the

benefit of game rather than nongame species. Stoddard (1936)

recommended the maintenance of existing openings and

construction of new openings in heavily forested lands for

the benefit of Wild Turkey, whose poults forage in clearings.

Provision of forest openings for turkey, quail, grouse, deer,

and other game animals quickly became a dominant feature of











wildlife management on public lands (Larson 1967, McCaffery

and Creed 1969, Healey and Nenno 1983).

The optimum size of maintained openings for different

species has been debated (Patric 1966, McCaffery and Creed

1969, Segelquist and Rogers 1975). Because little research

has been conducted on optimum sizes of openings for nongame

birds, Taylor and Taylor (1979) recommended that a variety of

opening sizes be maintained. Recent research in Illinois

(Overcash and Roseberry 1987) determined that 0.1-0.2-ha

openings in mature deciduous forest were not large enough to

increase bird counts (species or individuals); edge effects

began with openings 0.3 ha in size. Brown-headed Cowbirds,

an indicator of deleterious edge effect (Brittingham and

Temple 1983), also appeared at this size, but were more

abundant in larger openings of 0.7-1.0 ha (Overcash and

Roseberry 1987). In Wisconsin, passerine nests within 35 m

of 0.01-0.2-ha openings were parasitized by cowbirds more

frequently than were nests further away, but the difference

was not significant; parasitism rates declined significantly

with distance from openings > 0.2 ha (Brittingham and Temple

1983).

In San Felasco Hammock, most bird species were

distributed throughout plots across the full range of opening

(gap) sizes, and bird densities were generally enhanced at

all gap sizes except for the very largest (a 0.32-ha

sinkhole-marsh opening), where densities were depressed.











There was no evidence of deleterious edge effects (e.g.,

cowbird parasitism or increased predation on artificial

nests) in or near even the largest gaps (Noss, in

preparation). Cowbirds presently are uncommon breeders in

this region, however, and only one successful parasitism (a

Red-eyed Vireo feeding cowbird young, B. Muschlitz, personal

communication) has been documented in the study area. More

research is needed to determine the size of opening at which

edge effects begin to occur, and the qualitative differences

in edge effects associated with natural versus artificial

openings.

Construction of openings in heavily stocked conifer

plantations and other close-canopied, even-aged forests may

be beneficial to nongame birds and other wildlife. In such

cases, small openings may simulate treefall gaps, which

because of young stand age are not occurring naturally, and

provide the herbaceous and shrub growth otherwise lacking in

the forest. If, however, the landscape is already heavily

fragmented with abundant clearcuts, other open areas, and

roads--all of which increase edge--constructing additional

openings could be counter-productive. Construction of large

openings may intensify deleterious edge effects on forest

interior species by further fragmenting the forest landscape

and favoring opportunistic, weedy species over species more

in need of protection (Robbins 1979, Noss 1983, Wilcove et

al. 1986). For guidance on management, a general rule is to











look to the regional landscape for context and to the needs

of the most sensitive species for specific direction (Noss

1983, 1987b, Harris 1984, Noss and Harris 1986).

The results of this study, which document attraction of

birds to edge and openings within plots, should not be

interpreted as supporting construction of artificial openings

or edge in natural forests. Artificially maintained openings

may differ from natural gaps in species composition and other

ecological properties (Denslow 1985). The structural

heterogeneity of San Felasco Hammock is due primarily to

natural processes. Natural gaps and bayheads were important

features of site heterogeneity and attracted high densities

of birds within plots. Because gaps provide concentrated

resources (food and nesting cover) for birds, management

strategies that maintain natural levels of horizontal

patchiness would be prudent.

Old-growth forests are naturally patchy, uneven-aged

systems that fractionate through natural disturbance into a

mosaic of developmental stages (Bormann and Likens 1979,

Oliver 1981, Whitney 1987); hence, they provide the

heterogeneity required by native species at no cost to

managers. Despite early impressions that old-growth forests

were wildlife-poor, contemporary wildlife ecologists

recognize the richness of this system (Meslow et al. 1981,

Schoen et al. 1981, Harris 1984). Because birds may respond

less to edge in patchy areas of forest than in more












homogeneous sites (this study), maturation of forests to old-

growth potentially could ameliorate deleterious edge effects

associated with fragmentation, i.e., edge could become less

of an "ecological trap" (sensu Gates and Gysel 1978).

Exceptions to the rule of maintaining unmanipulated stands of

maturing forest would occur when sites are too small to

incorporate the natural disturbance regime and maintain

habitat diversity (Pickett and Thompson 1978, White and

Bratton 1980, Shugart and West 1981, Noss 1987a, Urban et al.

1987) or if the needs of particular endangered species

dependent on successional habitat take precedence over

community-level management.



A Final Comment on Scale and Observation

Birds appear to evaluate habitat suitability at several

spatial scales (Ambuel and Temple 1983, Hutto 1985, Sherry

and Holmes 1985). Hence, there may be no fundamental scale

at which to assess bird-habitat relationships; the

appropriate scale for research depends on the specific

questions being asked. Conclusions are most meaningful when

they derive from several observational scales (Allen and

Starr 1982, Maurer 1985, Wiens 1985, 1986, O'Neill et al.

1986, Wiens et al. 1987).

Attraction of birds to edge and habitat patchiness at a

within-plot, but not at a between-plot, scale in this study

does not preclude reappearance of the relationship at a still











higher (e.g., between-forest) scale. In fact, a positive

association of both bird species richness and density with

habitat heterogeneity has been demonstrated repeatedly at

landscape, regional, and biogeographic scales (Williams 1964,

Wiens 1985, Boecklen 1986, Freemark and Merriam 1986).

San Felasco Hammock is larger, more mature, and more

heterogeneous than other hammocks in the region, and has a

richer avifauna (B. Muschlitz, personal communication, Harris

and Wallace 1984, personal observation). Although birds used

the entire between-plot range of habitat heterogeneity with

equal frequency, long-term research is needed to determine if

more heterogeneous sites are selected preferentially (cf.

Fretwell and Lucas 1969, Van Home 1983). Within plots, bird

activity was concentrated in gaps and other areas of dense

shrub-level vegetation. Edges were also attractive, possibly

because they provide selection cues similar to those of gaps

(Gates and Gysel 1978). Although many species were attracted

to both edge and internal patchiness, edge birds were not

equivalent to gap birds. Some species (e.g., Indigo Bunting)

were attracted to edge but were not found in gaps, whereas

others (e.g., Hooded Warbler) were associated with gaps but

avoided edge. These results suggest that species respond

uniquely to opening size and other habitat features.

The research reported here was correlative rather than

experimental because the site is protected as a preserve.

Therefore, mechanisms that controlled habitat selection could











only be inferred. Observed relationships ideally should be

tested by more rigorous experimental methods, but it is

premature to conclude that "further descriptive and

correlative studies can tell us little more that is new"

(Morse 1985:153). Although manipulations that create

different levels of heterogeneity may be useful,

observational studies spanning a breadth of spatial and

temporal observation scales can answer many questions about

habitat selection without modifying the small amount of

natural area that remains.















LITERATURE CITED


Allen, T.F.H., and Starr, T.B. 1983. Hierarchy: Perspectives
for ecological complexity. University of Chicago Press,
Chicago, Illinois, USA.

Ambuel, B., and S.A. Temple. 1983. Area-dependent changes in
the bird communities and vegetation of southern
Wisconsin forests. Ecology 64: 1057-1068.

American Ornithologists' Union (AOU). 1983. Check-list of
North American birds. Sixth edition. American
Ornithologists' Union, Washington, D.C., USA.

Ansley, C.C. 1952. An ecological comparison of the mesic
hardwood forests of central Florida. Thesis.
University of Florida, Gainesville, Florida, USA.

Beecher, W. 1942. Nesting birds and the vegetation
substrate. Chicago Ornithological Society, Chicago,
Illinois, USA.

Bider, J.R. 1968. Animal activity in uncontrolled
terrestrial communities as determined by a sand
transect technique. Ecological Monographs 38: 269-308.

Blake, J.G., and W.G. Hoppes. 1986. Influence of resource
abundance on use of treefall gaps by birds. Auk 103:
328-340.

Boecklen, W.J. 1986. Effects of habitat heterogeneity on the
species-area relationships of forest birds. Journal of
Biogeography 13: 59-68.

Bormann, F.H., and G.E. Likens. 1979. Pattern and process in
a forested ecosystem. Springer-Verlag, New York, New
York, USA.

Braun, E.L. 1950. Deciduous forests of eastern North
America. Macmillan, New York, New York, USA.

Bray, J.R. 1956. Gap phase replacement in a maple-basswood
forest. Ecology 37: 598-600.











Brittingham, M.C., and S.A. Temple. 1983. Have cowbirds
caused forest songbirds to decline? BioScience 33: 31-
35.

Brokaw, N.V.L. 1985. Treefalls, regrowth, and community
structure in tropical forests. Pages 53-69 in S.T.A.
Pickett and P.S. White, editors. The ecology of natural
disturbance and patch dynamics. Academic Press,
Orlando, Florida, USA.

Carpenter, J.R. 1935. Forest edge birds and exposures of
their habitats. Wilson Bulletin 47: 106-108.

Chasko, G.G., and J.E. Gates. 1982. Avian habitat
suitability along a transmission-line corridor in an
oak-hickory forest region. Wildlife Monographs 82: 1-
41.

Christman, S.P. 1984. Plot mapping: Estimating densities of
breeding bird territories by combining spot mapping and
transect techniques. Condor 86: 237-241.

Clewell, A.F. 1981. Natural setting and vegetation of the
Florida Panhandle. United States Army Corps of
Engineers, Contract No. DACWO1-77-C-0104. Mobile,
Alabama, USA.

Cody, M.L. 1985. Habitat selection in birds. Academic Press,
Orlando, Florida, USA.

Cooper, W.S. 1913. The climax forest of Isle Royale, Lake
Superior, and its development. Botanical Gazette 55: 1-
44, 115-140, 189-235.

Cottam, G., and J.T. Curtis. 1956. The use of distance
measures in phytosociological sampling. Ecology 37:
451-460.

den Boer, P.J. 1981. On the survival of populations in a
heterogeneous and variable environment. Oecologia
(Berlin) 50: 39-53.

Denslow, J.S. 1985. Disturbance-mediated coexistence of
species. Pages 307-323 in S.T.A. Pickett and P.S.
White, editors. The ecology of natural disturbance and
patch dynamics. Academic Press, Orlando, Florida, USA.

Dohrenwend, R.E. 1978. The climate of Alachua County,
Florida. IFAS Agricultural Experiment Station Bulletin
796, University of Florida, Gainesville, Florida, USA.











Dunn, W.J. 1982. Plant communities and vascular flora of San
Felasco Hammock, Alachua County, Florida. Thesis.
University of Florida, Gainesville, Florida, USA.

Emlen, J.T. 1971. Population densities of birds derived from
transect counts. Auk 88: 323-342.

Emlen, J.T. 1984. An observer-specific, full-season, strip-
map method for censusing songbird communities. Auk 101:
730-740.

Ewel, J.J., and R.W. Simons. 1976. The vegetation of San
Felasco. Pages 20-28 in A plan to place San Felasco in
public ownership. Unpublished, Gainesville, Florida,
USA.

Faaborg, J. 1980. Potential uses and abuses of diversity
concepts in wildlife management. Transactions of the
Missouri Academy of Science 14: 41-49.

Forman, R.T.T., A.E. Galli, and C.F. Leck. 1976. Forest size
and avian diversity in New Jersey woodlots with some
land use implications. Oecologia (Berlin) 26: 1-8.

Forman, R.T.T., and M. Godron. 1981. Patches and structural
components for a landscape ecology. BioScience 31: 733-
740.

Forman, R.T.T., and M. Godron. 1986. Landscape ecology. J.
Wiley, New York, New York, USA.

Freemark, K.E., and H.G. Merriam. 1986. Importance of area
and habitat heterogeneity to bird assemblages in
temperate forest fragments. Biological Conservation 36:
115-141.

Fretwell, S.D., and H.L. Lucas. 1969. On territorial
behavior and other factors influencing habitat
distribution in birds. I. Theoretical development. Acta
Biotheoretica 19: 16-36.

Galli, A.E., C.F. Leck, and R.T.T. Forman. 1976. Avian
distribution patterns in forest islands of different
sizes in central New Jersey. Auk 93: 356-364.

Gates, J.E., and L.W. Gysel. 1978. Avian nest dispersion and
fledging success in field-forest ecotones. Ecology 59:
871-883.

Gates, J.E., and J.A. Mosher. 1981. A functional approach to
estimating habitat edge width for birds. American
Midland Naturalist 105: 189-192.











Gauch, H.G. 1982. Multivariate analysis in community
ecology. Cambridge University Press, New York, New
York, USA.

Gilbert, L.E. 1980. Food web organization and the
conservation of neotropical diversity. Pages 11-33 in
M.E. Soule and B.A. Wilcox, editors. Conservation
biology: An evolutionary-ecological perspective.
Sinauer Associates, Sunderland, Massachusetts, USA.

Good, E.E., and C.A. Dambach. 1943. Effect of land use
practices on breeding bird populations in Ohio. Journal
of Wildlife Management 7: 291-297.

Greig-Smith, P. 1964. Quantitative plant ecology, 2nd
edition. Butterworth, London, England.

Gutzwiller, K.J., and S.H. Anderson. 1987. Multiscale
associations between cavity-nesting birds and features
of Wyoming streamside woodlands. Condor 89: 534-548.

Hansson, L. 1979. On the importance of landscape
heterogeneity in northern regions for the breeding
population densities of homeotherms: A general
hypothesis. Oikos 33: 182-189.

Harper, R.M. 1905. "Hammock," "hommock," or "hummock?"
Science, New Series 22: 400-402.

Harper, R.M. 1911. The relation of climax vegetation to
islands and peninsulas. Bulletin of the Torrey
Botanical Society 38: 515-525.

Harris, L.D. 1980. Forest and wildlife dynamics in the
southeast. Transactions of the North American Wildlife
and Natural Resources Conference 45: 307-322.

Harris, L.D. 1984. The fragmented forest: Island
biogeographic theory and the preservation of biotic
diversity. University of Chicago Press, Chicago,
Illinois, USA.

Harris, L.D., and J.D. McElveen. 1981. Effect of forest
edges on north Florida breeding birds. School of Forest
Resources and Conservation, University of Florida,
Intensive Management Practices Assessment Center Report
6(4): 1-24.










Harris, L.D., and W. Smith. 1978. Relations of forest
practices to non-timber resources and adjacent
ecosystems. Pages 28-53 in T. Tippen, editor.
Principles of maintaining productivity on prepared
sites. USDA Forest Service, New Orleans, Louisiana,
USA.

Harris, L.D., and R. Wallace. 1984. Breeding bird species in
Florida forest fragments. Proceedings of the Annual
Conference of the Southeastern Association of Fish and
Wildlife Agencies 38: 87-96.

Harrison, H.H. 1975. A field guide to birds' nests. Houghton
Mifflin, Boston, Massachusetts, USA.

Harrison, S. 1987. Treefall gaps versus forest understory as
environments for a defoliating moth on a tropical
forest shrub. Oecologia (Berlin) 72: 65-68.

Hartshorn, G.S. 1978. Treefalls and tropical forest
dynamics. Pages 617-628 in P.B. Tomlinson and M.H.
Zimmerman, editors. Tropical trees as living systems.
Cambridge University Press, New York, New York, USA.

Helle, E., and P. Helle. 1982. Edge effect on forest bird
densities on offshore islands in the northern Gulf of
Bothnia. Annals Zoologica Fennici 19: 165-169.

Healey, W.M., and E.S. Nenno. 1983. Minimum maintenance
versus intensive management of clearings for wild
turkeys. Wildlife Society Bulletin 11: 113-120.

Hilden, O. 1965. Habitat selection in birds. Annals
Zoologica Fennici 2: 53-75.

Hurlbert, S.H. 1984. Pseudoreplication and the design of
ecological field experiments. Ecological Monographs 54:
187-211.

Hutto, R.L. 1985. Habitat selection by nonbreeding,
migratory land birds. Pages 455-476 in M.L. Cody,
editor. Habitat selection in birds. Academic Press,
Orlando, Florida, USA.

James, F.C. 1971. Ordinations of habitat relationships among
breeding birds. Wilson Bulletin 83: 215-236.

Johnston, D.W. 1970. High density of birds breeding in a
modified deciduous forest. Wilson Bulletin 82: 79-82.











Johnston, D.W., and E.P. Odum. 1956. Breeding bird
populations in relation to plant succession on the
piedmont of Georgia. Ecology 37: 50-62.

Johnston, V.R. 1947. Breeding birds of the forest edge in
east-central Illinois. Condor 49: 45-53.

Karr, J.R., and K.E. Freemark. 1983. Habitat selection and
environmental gradients: dynamics in the "stable"
tropics. Ecology 64: 1481-1494.

Karr, J.R., and R.R. Roth. 1971. Vegetation structure and
avian diversity in several New World areas. American
Naturalist 105: 423-435.

Kartesz, J.T., and R. Kartesz. 1980. A synonymized checklist
of the vascular flora of the United States, Canada, and
Greenland. University of North Carolina Press, Chapel
Hill, North Carolina, USA.

Kendeigh, S.C. 1944. Measurement of bird populations.
Ecological Monographs 14: 67-106.

Kroodsma, R.L. 1982. Edge effect on breeding forest birds
along a power-line corridor. Journal of Applied Ecology
19: 361-370.

Kroodsma, R.L. 1984. Effect of edge on breeding forest bird
species. Wilson Bulletin 96: 426-436.

Kurz, H., and R.K. Godfrey. 1962. Trees of northern Florida.
University of Florida Press, Gainesville, Florida, USA.

Larson, J.S. 1967. Forests, wildlife, and habitat manage-
ment--A critical examination of practice and need. USDA
Forest Service Research Paper SE-30.

Lay, D. 1938. How valuable are woodland clearings to
birdlife? Wilson Bulletin 50: 254-256.

Leopold, A. 1933. Game management. Charles Scribners Sons,
New York, New York, USA.

Leopold, A. 1938. Report on Huron Mountain Club. Huron
Mountain Club, Huron Mountain, Michigan, USA.

Linhart, Y.B., P. Feinsinger, J.H. Beach, W.H. Busby, K.G.
Murray, W.Z. Pounds, S. Kinsman, C.A. Guindon, and M.
Kooiman. 1987. Disturbance and predictability of
flowering patterns in bird-pollinated cloud forest
plants. Ecology 68: 1696-1710.











Lovejoy, T.E., R.O. Bierregaard, A.B. Rylands, J.R. Malcolm,
C.E. Quintela, L.H. Harper, K.S. Brown, A.H. Powell,
G.V.N. Powell, H.O.R. Schubart, and M.B. Hays. 1986.
Edge and other effects of isolation on Amazon forest
fragments. Pages 257-285 in M.E. Soule, editor.
Conservation biology: the science of scarcity and
diversity. Sinauer Associates, Sunderland,
Massachusetts, USA.

MacArthur, R.H., and J.W. MacArthur. 1961. On bird species
diversity. Ecology 42: 594-598.

MacArthur, R.H., J.W. MacArthur, and J. Preer. 1962. On bird
species diversity--Prediction of bird censuses from
habitat measurements. American Naturalist 96: 167-174.

May, R.M. 1986. The search for patterns in the balance of
nature: Advances and retreats. Ecology 67: 1115-1126.

Martin, T.E. 1988. Habitat and area effects on forest bird
assemblages: Is nest predation an influence? Ecology
69: 74-84.

Martin, T.E., and Karr, J.R. 1986. Patch utilization by
migrating birds: Resource oriented? Ornis Scandinavica
17: 165-174.

Maurer, B.A. 1985. Avian community dynamics in desert
grasslands: Observational scale and hierarchical
structure. Ecological Monographs 55: 295-312.

McCaffery, K.R., and W.A. Creed. 1969. Significance of
forest openings to deer in northern Wisconsin.
Wisconsin Department of Natural Resources Technical
Bulletin No. 44.

Merriam, G. 1988. Landscape dynamics in farmland. Trends in
Ecology and Evolution 3: 16-20.

Meslow, E.C., C. Maser, and J. Verner. 1981. Old-growth
forests as wildlife habitat. Transactions of the North
American Wildlife and Natural Resources Conference 46:
329-335.

Monk, C.D. 1965. The southern mixed hardwoods of north
central Florida. Ecological Monographs 35: 335-354.

Morse, D.H. 1985. Habitat selection in North American
parulid warblers. Pages 131-157 in M.L. Cody, editor.
Habitat selection in birds. Academic Press, Orlando,
Florida, USA.












Nelson, M.M., R.A. Chesness, and S.W. Harris. 1960.
Relationship of pheasant nests to hayfield edges.
Journal of Wildlife Management 24: 430.

Noss, R.F. 1981. The birds of Sugarcreek, an Ohio nature
reserve. Ohio Journal of Science 81: 29-40.

Noss, R.F. 1983. A regional landscape approach to maintain
diversity. BioScience 33: 700-706.

Noss, R.F. 1987a. From plant communities to landscapes in
conservation inventories: A look at The Nature
Conservancy (USA). Biological Conservation 41: 11-37.

Noss, R.F. 1987b. Protecting natural areas in fragmented
landscapes. Natural Areas Journal 7: 2-13.

Noss, R.F., and L.D. Harris. 1986. Nodes, networks, and
MUMs: preserving diversity at all scales. Environmental
Management 10: 299-309.

Noss, R.F., H.W. Kale, and C.W. Biggs. 1985. Florida
breeding bird atlas: handbook for cooperators. Florida
Audubon Society, Maitland, Florida, USA.

Oliver, C.D. 1981. Forest development in North America
following major disturbances. Forest Ecology and
Management 3: 153-168.

O'Neill, R.V., D.L. DeAngelis, J.B. Waide, and T.F.H. Allen.
1986. A hierarchical concept of ecosystems. Princeton
University Press. Princeton, New Jersey, USA.

Overcash, J.L., and J.L. Roseberry. 1987. Evaluation of
Shawnee National Forest wildlife openings. Cooperative
Wildlife Research Laboratory, SIU-C. Southern Illinois
University, Carbondale, Illinois, USA.

Patric, E.F. 1966. An evaluation of the size an shape of
forest clearings. New York Bureau of Game, Final
Report, Federal Aid Project W-105-R-6, Job 1-A.

Pickett, S.T.A., and J.N. Thompson. 1978. Patch dynamics and
the size of nature reserves. Biological Conservation
13: 27-37.

Pickett, S.T.A., and P.S. White. 1985. The ecology of
natural disturbance and patch dynamics. Academic Press,
Orlando, Florida, USA.











Platt, W.J., and S.M. Herman. 1986. Relationships between
dispersal syndrome and characteristics of populations
of trees in a mixed-species forest. Pages 309-321 in A.
Estrada, T.H. Fleming, C. Vasques-Yanes, and R. Dirzo,
editors. Frugivores and seed dispersal. Dr. W. Junk,
The Hague, The Netherlands.

Platt, W.J., and M. Schwartz. in press. Mixed species
southern hardwood forests. In Ecosystems of Florida.
Academic Press, Orlando, Florida, USA.

Quarterman, E., and C. Keever. 1962. Southern mixed hardwood
forests: climax in the southeastern coastal plain,
U.S.A. Ecological Monographs 32: 167-185.

Recher, H. 1969. Bird species diversity and habitat
diversity in Australia and North America. American
Naturalist 103: 75-80.

Repenning, R.W., and R.F. Labisky. 1985. Effects of even-age
timber management on bird communities of the longleaf
pine forest in northern Florida. Journal of Wildlife
Management 49: 1088-1098.

Risser, P.G., J.R. Karr, and R.T.T. Forman. 1984. Landscape
ecology: directions and approaches. Illinois Natural
History Survey Special Publication 2: 1-18.

Robbins, C.S. 1979. Effect of forest fragmentation on bird
populations. Pages 198-212 in R.M. DeGraaf and K.E.
Evans, editors. Proceedings of the workshop, Management
of north central and northeastern forests for nongame
birds. United States Forest Service General Technical
Report NC-51.

Roth, R.R. 1976. Spatial heterogeneity and bird species
diversity. Ecology 57: 773-782.

Roth, R.R. 1977. Vegetation as a determinant in avian
ecology. Proceedings of the Welder Wildlife Foundation
Symposium 1: 162-174.

Runkle, J.R. 1981. Gap regeneration in some old-growth
forests of the eastern United States. Ecology 62: 1041-
1051.

Runkle, J.R. 1982. Patterns of disturbance in some old-
growth mesic forests of eastern North America. Ecology
63: 1533- 1546.












Runkle, J.R. 1985. Disturbance regimes in temperate forests.
Pages 17-33 in S.T.A. Pickett and P.S. White, editors.
The ecology of natural disturbance and patch dynamics.
Academic Press, Orlando, Florida.

Samson, F.B., and F.L. Knopf. 1982. In search of a diversity
ethic for wildlife management. Transactions of the
North American Wildlife and Natural Resources
Conference 47: 421- 431.

Schemske, D.W., and N. Brokaw. 1981. Treefalls and the
distribution of understory birds in a tropical forest.
Ecology 62: 938-945.

Schoen, J.W., O.C. Wallmo, and M.D. Kirchhoff. 1981.
Wildlife-forest relationships: is a reevaluation of
old-growth necessary? Transactions of the North
American Wildlife and Natural Resources Conference 46:
531-544.

Segelquist, C., and M. Rogers. 1975. Use of wildlife forage
clearings by white-tailed deer in the Arkansas Ozarks.
Proceedings of the Southeastern Association of Game and
Fish Commissioners 29: 568-573.

Shelford, V.E. 1913. Animal communities in temperate America
as illustrated in the Chicago region. University of
Chicago Press, Chicago, Illinois, USA.

Shelford, V.E. 1927. Animal communities in temperate America.
Bulletin of the Geographical Society of Chicago 5: 1-
362.

Sherry, T.W., and R.T. Holmes. 1985. Dispersion patterns and
habitat responses of birds in northern hardwood
forests. Pages 283-309 in M.L. Cody, editor. Habitat
selection in birds. Academic Press, Orlando, Florida,
USA.

Shugart, H.H., and D.C. West. 1981. Long-term dynamics of
forest ecosystems. American Scientist 69: 647-652.

Skeate, S.T. 1987. Interactions between birds and fruits in
a northern Florida hammock community. Ecology 68: 297-
309.

Sokal, R.R., and F.J. Rohlf. 1981. Biometry, 2nd edition.
W.H. Freeman, New York, New York, USA.

Stoddard, H.L. 1936. Management of wild turkey. Transactions
of the North American Wildlife Conference 1: 352-356.











Strelke, W.K., and J.G. Dickson. 1980. Effect of forest
clear-cut edge on breeding birds in east Texas. Journal
of Wildlife Management 44: 559-567.

Taylor, C.M., and W.E. Taylor. 1979. Birds of upland
openings. Pages 189-197 in R.M. DeGraaf and K.E. Evans,
editors. Proceedings of the workshop, Management of
north central and northeastern forests for nongame
birds. United States Forest Service General Technical
Report NC-51.

Thomas, J.W., C. Maser, and J.E. Rodiek. 1979. Edges. Pages
48-59 in J.W. Thomas, editor. Wildlife habitats in
managed forests: the Blue Mountains of Oregon and
Washington. United States Forest Service Agricultural
Handbook No. 553.

Urban, D.L., R.V. O'Neill, and H.H. Shugart. 1987. Landscape
ecology. BioScience 37: 119-127.

Van Home, B. 1983. Density as a misleading indicator of
habitat quality. Journal of Wildlife Management 47:
893-901.

Wales, B.A. 1972. Vegetational analysis of north and south
edges in a mature oak-hickory forest. Ecological
Monographs 42: 451-471.

Watt, A.S. 1925. On the ecology of British beechwoods with
special reference to their regeneration. Journal of
Ecology 13: 27-73.

Watt, A.S. 1947. Pattern and process in the plant community.
Journal of Ecology 35: 1-22.

Whitcomb, R.F., J.F. Lynch, P.A. Opler, and C.S. Robbins.
1976. Island biogeography and conservation: strategy
and limitations. Science 193: 1030-1032.

Whitcomb, R.F., C.S. Robbins, J.F. Lynch, B.L. Whitcomb, K.
Klimkiewicz, and D. Bystrak. 1981. Effects of forest
fragmentation on avifauna of the eastern deciduous
forest. Pages 125-205 in R.L. Burgess and D.M. Sharpe,
editors. Forest island dynamics in man-dominated
landscapes. Springer-Verlag, New York, New York, USA.

White, P.S. 1979. Pattern, process, and natural disturbance
in vegetation. Botanical Review 45: 229-299.












White, P.S., and S.P. Bratton. 1980. After preservation:
Philosophical and practical problems of change.
Biological Conservation 18: 241-255.

White, T.C.R. 1984. The abundance of invertebrate herbivores
in relation to the availability of nitrogen in stressed
food plants. Oecologia (Berlin) 63: 90-105.

Whitney, G.G. 1987. Some reflections on the value of old-
growth forests, scientific and otherwise. Natural Areas
Journal 7: 92-99.

Wiens, J.A. 1985. Habitat selection in variable
environments: Shrub-steppe birds. Pages 227-251 in M.L.
Cody, editor. Habitat selection in birds. Academic
Press, Orlando, Florida, USA.

Wiens, J.A. 1986. Spatial scale and temporal variation in
studies of shrubsteppe birds. Pages 154-172 in J.
Diamond and T.J. Case. Community ecology. Harper & Row,
New York, New York, USA.

Wiens, J.A., J.T. Rotenberry, and B. Van Horne. 1987.
Habitat occupancy patterns of North American
shrubsteppe birds: The effects of spatial scale. Oikos
48: 132-147.

Wilcove, D.S., C.H. McClellan, and A.P. Dobson. 1986.
Habitat fragmentation in the temperate zone. Pages 237-
256 in M.E. Soule, editor. Conservation biology: The
science of scarcity and diversity. Sinauer Associates,
Sunderland, Massachusetts, USA.

Wilkinson, L. 1987. SYSTAT: the system for statistics.
SYSTAT, Evanston, Illinois, USA.

Williams, C.B. 1964. Patterns in the balance of nature.
Academic Press, New York, New York, USA.

Williamson, G.B. 1975. Pattern and seral composition in an
old-growth beech-maple forest. Ecology 56: 727-731.

Wolda, H., and R. Foster. 1978. Zunacetha annulata
(Lepidoptera; Dioptidae), an outbreak insect in a
neotropical forest. Geo-Eco-Trop 2: 443-454.