Title: Population biology of the American crocodile
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Title: Population biology of the American crocodile
Physical Description: Book
Creator: Kushlan, James A.
Mazzotti, Frank J.
Affiliation: University of Mississippi -- Department of Biology
Pennsylvania State University -- School of Forest Resources
Publisher: Society for the Study of Amphibians and Reptiles
Publication Date: 1989
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General Note: Drawn from Journal of Herpetology, Vol. 23, No. 1, pp. 7-21, 1989
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Bibliographic ID: UF00066442
Volume ID: VID00001
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Journal of Herpetology, Vol. 23, No. 1, pp. 7-21, 1989
Copyright 1989 Society for the Study of Amphibians and Reptiles

Population Biology of the American Crocodile


JAMES A. KUSHLAN1 AND FRANK J. MAZZOTTI23

'Department of Biology, University of Mississippi, University, Mississippi 38655, USA
2School of Forest Resources, Pennsylvania State University, University Park, Pennsylvania 16802, USA

ABSTRACT. The population biology of the American crocodile (Crocodylus acutus) was studied in south-
ern Florida during 1977-1982. Crocodiles occur primarily in inland mangrove swamps protected from wave
action. Females use the open waters of Florida Bay only for access to nesting sites. Individuals have large
(86-262 ha), overlapping activity areas. Nesting occurs in spring and summer, avoiding the cold and the
wet seasons, either of which can affect incubation. Clutches averaging 38 eggs were laid both in mounds
and in holes in the ground, either singly or communally. Available data cannot support the view that the
number of nests has decreased in recent years. Hatching failure occurred as a result of infertility, predation,
and embryonic mortality from desiccation and flooding. Hole and creek nests were most susceptible to
embryonic mortality. Seventy-eight percent of nests hatched some young. We found no evidence of adults
defending nests or young, but nest opening by adults was essential for hatching. Disturbance at nest sites
caused females to abandon the site. All expected age classes occurred in the population. Size at maturity
was 2.25 m TL for females. Documented mortality of adults and subadults of approximately 2 crocodiles
per year was predominantly human-caused. At least 45 crocodiles have been released into southern Florida
in 17 years. We estimate the southern Florida population to be about 220 78 adults and subadults.


The northernmost population of the Ameri-
can crocodile (Crocodylus acutus) occurs on the
extreme southern tip of the Florida peninsula,
USA. The range of this tropical species has al-
ways been limited, probably by temperature
constraints (Kushlan and Mazzotti, 1989). Early
reports of crocodiles in Florida are notices and
discussions of its occurrence (Wyman, 1870;
Hornaday, 1891; Smith, 1896; Barbour, 1923);
Moore (1953) provided the first detailed account
of its status. Ogden (1978) documented aspects
of its nesting biology. More recently, Gaby et
al. (1985) reported on the population biology
of a small number of crocodiles living in a pow-
er plant cooling system.


3 Present Address: Department of Wildlife and
Range Sciences, University of Florida, 3245 College
Avenue, Davie, Florida 33314, USA.


Many crocodilian populations are endan-
gered because their effective population sizes
have been reduced by human-related factors
such as as hunting and habitat loss. Small pop-
ulations, particularly when isolated, risk extir-
pation because of the action of natural or arti-
ficial forces that erode their numbers. The
Florida population of the American crocodile is
thought to be of limited size (Ogden, 1978), and
therefore susceptible to chance and human in-
terference. As a result it has long been consid-
ered to be endangered (Barbour, 1923; Hines et
al., 1984). Unfortunately, limited information
has inhibited understanding of its population
biology, and therefore of its true status or ap-
propriate conservation needs.
In this paper we discuss the population bi-
ology of the the American crocodile based on
a five-year study of the population in the core
of its northernmost range, northeastern Florida





J. A KUSHLAN AND F. J. MAZZOTTI


Bay. Where appropriate, we compare informa-
tion from studies conducted simultaneously and
cooperatively with our own on other segments
of the population (Gaby et al., 1975; P. Moler,
pers. comm.). Other aspects of our overall study
program are discussed elsewhere (Behler, 1978;
Hall et al., 1979; Dunson, 1982; Lutz and Dun-
bar-Cooper, 1984; Stoneburnei and Kushlan,
1984; Kushlan, 1988; Mazzotti et al 1988; Kush-
lan and Mazzotti, 1989).

STUDY SITE
The study was conducted in southern Florida
in the core range of the North American pop-
ulation (Kushlan and Mazzotti, 1989), primarily
in northeastern Florida Bay (Fig. 1). Much of
the Florida peninsula is covered by freshwater
marshes, including the Everglades, which are
confluent along the coast with mangrove
swamps dominated by red mangrove (Rhyzo-
phora mangle). Within the swamps are relatively
deep-water pools, lakes, creeks, and flats that
are protected from wind and wave action. Pools
and lakes tend to be about 1 m deep, lack emer-
gent vegetation, and are surrounded by man-
grove trees. Creeks are short rivers, in places
bordered by an elevated bank. Sand beaches are
limited to the shores of islands and spits in
Florida Bay, which averages 1.25 m deep. The
shoreline of Florida Bay is exposed to wind and
wave action except in coves.
Rainfall is seasonal; 75 to 80% of the 1150-
1400 mm annual precipitation falls during a
May to October rainy season. Salinity fluctuates
with rainfall, runoff, and evaporation, and is
highest in coastal bays and lower in inland
mangrove swamps. Lunar tidal fluctuation in
the northeastern portion of Florida Bay is min-
imal because circulation is dampened by islands
(called keys) and mud banks. Water levels fluc-
tuate in response to upland water discharge,
seasonal changes in sea surface elevation, and
wind.
METHODS
The study was conducted from 1977 to 1982.
Crocodiles were located on standardized
monthly surveys using boat, canoe, fixed-wing
airplane, and helicopter (Kushlan and Mazzotti,
1989). For each crocodile seen, we recorded the
location, time, size (estimated to the nearest
quarter meter), and habitat. An extensive cap-
ture/mark/release program was conducted us-
ing boats at night. After capturing a crocodile
by hand or neck noose, we determined total
length (TL), snout-vent length (SVL; to poste-
rior margin of the cloaca), and sex (Chabreck,
1966). Crocodiles were marked by toe web-tags
(monel poultry tags), a unique combination of


tached to tail scutes and to a flexible plastic neck
collar. At capture sites, and at observation sites
during helicopter and boat surveys, we mea-
sured air and water temperatures, salinity, wave
action, and water depth. Water level, salinity,
and temperature were monitored at several sites.
We captured and tagged 57 adults and sub-
adults and 359 hatchlings from 23 clutches (40%
of estimated production); 192 were tagged with-
in 24 hours of hatching. Most captures of non-
hatchlings were made away from -nests, but in
one year 8 females were trapped near, but not
on, nest sites. Because of the responses of these
animals in abandoning their nests (see below),
the exercise was not repeated. It did provide an
inadvertent experiment on disturbance effects.
Observations of adults and hatchlings in other
years were made with considerable care to avoid
disturbance.
The wariness and difficulty of capture of
American crocodiles and its endangered status
made recapture difficult, and thus we could not
use mark/recapture methods to calculate pop-
ulation size. We use the method devised by
Chabreck (1966): P = N/AFE, where N is the
number of nests, A is the percentage of adults
in the population, F is the percentage of females
in the adult population, and E is the percentage
of the females nesting. Values are given 1
standard error.
Nests were found by searching the shoreline
on foot or using helicopters. Each potential nest
site was excavated for eggs, which were im-

mediately reburied without turning. Fertility of
each egg was determined by its banding (Fer-
guson, 1982). Sites were monitored through in-
cubation to determine the fate of the eggs. Signs
of predation, flooding, adult visitation, and
hatching were noted. Temperature, rainfall, and
salinity at each site were monitored. In the first
year, we excavated and frequently visited only
4 of 11 sites to test whether these activities af-
fected their survival (Dietz and Hines, 1980) or
the return of the female at hatching. Because
one test site and one control site were predated,
and all were opened at hatching, we concluded
that our activities had no adverse effect.
We attempted to obtain all available infor-
mation on nests and nesting in southern Flor-
ida. These data came from the literature (Moore,
1953; Ogden, 1978; Gaby et al., 1985), from per-
sonal communications with those also studying
Florida crocodiles (J. Lang, R. Gaby, and P. Mo-
ler), and from the files of Everglades National
Park and of Joseph Moore (pers. comm.), who
carefully assembled previous information and
interviewed long-term residents of Florida Bay
in the 1950s.
Radio transmitters (SB2 for adults and 5 gram











IA I


FLORDA BAY




FIG. 1. Map of southern Florida, showing

neapolis, Minnesota) were attached to neck col-
lars (having a 1 yr life) or dacron back harnesses.
Telemetered and non-telemetered hatchlings
moved together, indicating that telemeters did
not restrict movement. Fixes were obtained on
weekly fixed-wing aircraft flights. Activity areas
were calculated from telemetry fixes using the
modified minimum area method (Harvey and
Barbour, 1965).
The relative abundance of each habitat type
was determined by placing a 0.5 cm acetate grid
over a USGS T-map (1:20,000) of the study area.
The habitat under each grid intersection was
identified and tallied.

RESULTS
Habitat Use.--Crocodiles in southern Florida
used mangrove swamps. Their use of habitat


//KEY
SLARGO
TURKEY






PySi


25km


principal localities mentioned in the text.


was nonrandom for all but one comparison of
distribution among habitats (Table 1). Over 50%
of our observations were in inland ponds and
creeks, and an additional 25% were in protected
coves. Only 6% were along exposed shorelines,
and a few were on shallow mud flats in the
interiors of large islands. The habitats used fre-
quently were characterized by relatively deep
water (>1 m) and protection from wind and
wave action. Creek banks provided cave and
basking sites. Crocodiles tended to remain near
shorelines; only two crocodiles were observed
in open water.
Crocodiles used habitats characterized by low
salinities, averaging 14 ppt (t = 13.8, SD = 10.0,
range 0-35 ppt, N = 111). Crocodiles were found
in higher salinities in spring and summer (x =
17.8, SD = 9.5, range = 0-35 ppt, N = 53) than


-TABLE 1. Habitat use by subadult and adult American crocodiles, given as percent of all habitats. The
percent of habitat area available is noted under each habitat. Preference tested using a chi-square test.

Mangrove Exposed
Number of Ponds Creeks Coves flats shoreline
observations (15%) (10%) (43%) (8%) (24%) P


Total
Non-breeding
Breeding
Adult
Subadult
Males
Females


6 <0.001
1 <0.001
14 <0.001
10 <0.001
4 ns
0 <0.001
2 <0.001


~r~RGL~S~S


















0-5 6-10 fl-1516-20 21-25


SEPTEMBER


Si I I i 1r-
2 0-5 6-10 11-15 16-20 21-25 2
30 --

MARC
0-5 6-10 11-15 16-20 21-25 26
Z 30

MARC




0-5 6-10 11-15 16-20 21-25 26
SALINITY %.
FIG. 2. Crocodile sightings in differ
overall and for the breeding (Mar.-Ai
breeding (Sept.-Feb.) seasons.

in winter and fall (x = 9.8, SD =
0-31 ppt, N = 58), when the anim
land and fresh water discharge was
test, P < 0.001). In view of the seas
salinities present in Florida Bay (oft
the relatively low salinities used b
show a distinct habitat preference
brackish water. This preferential
onstrated by the preponderance of
fresh to brackish water (Fig. 2).
Seasonal differences in crocodile
(Fig. 2) are attributable to excursion
ida Bay for nesting. In fall and wi
diles confine themselves to the inla
bays, and creeks (Fig. 3). In spring a
animals also occurred on exposed sh
coves of Florida Bay, a shift reflect
ences in habitat use during the I
non-breeding seasons (Table 1).
Hatchling crocodiles occurred ii
mangrove roots, under shoreline
holes, or under beach wrack by da)
water at the shore at night. Use o
minimizes exposure to temperatui
high salinity, wave action, and p
dation. Older juveniles used creeks
which seemed to constitute the prin
habitats in that they were character.
term juvenile occupancy. Swift cur


middle of the creek were normally avoided. A
OVERALL combination of shoreline vegetation and ledges
at water level provided protection from wave
action and current.
Activity Areas and Movements.--Activity areas
of 5 animals with >18 fixes averaged 107 ha
(SD = 71.3, range 86-262 ha). These activity
areas overlapped considerably (Figs. 4, 5). These
results were derived from repeated radiotelem-
-'1 etry fixes, over as many as 28 'iionths per in-
26-30 31-35 dividual, on 10 adult and subadult crocodiles
(2 males, 8 females, 1.85-2.96 m TL). Teleme-
FEBRUARY tered crocodiles were frequently observed near
other crocodiles. We located one female with
other crocodiles on 6 occasions, 5 times near a
telemetered male. Thus the activity areas were
geographically and temporally non-exclusive.
r--31-3- Telemetry data demonstrated conclusively
that the seasonal use of Florida Bay was related
to nesting. Four telemetered females, known to
H-AUGUST be associated previously with nest sites on is-
lands in Florida Bay, moved into the bay only
during the nesting season. Three females left
their nest sites immediately after their young
hatched and returned to the inland mangrove
-30 31-35 swamps. One female moved after hatching to a
flooded flat within the nesting island where she
ent salinities, remained for 5 months prior to returning in-
ig.) and non- land. Neither telemetered inale was located in
Florida Bay.
Telemetry daia also showed that individual
8.8, range = females return to the same nesting area in sub-
als were in- sequent years. One returned to the same area
highest (U- over three years but alternated her nest site
ionally high from one side of a creek to the other.
en > 35 ppt), The pattern of area use included substantial
y crocodiles movement interspersed with periods of resi-
for fresh to dency (Fig. 5). One female stayed 38 days in a
use is dem- pond. Some animals appeared to have two sep-
sightings in arated activity areas. Females nesting in Florida
Bay showed this pattern. A male using two sep-
distribution arated areas had two periods of residency in a
ns into Flor- pond containing an active wading bird nesting
inter, croco- colony. Some recorded excursions include: a fe-
ind swamps, male moving 4.2 km in 6 days, a male moving
nd summer, 6 km in 6 days, and another male moving 16.2
orelines and km in 22 days. A subadult female, which ap-
ed in differ- peared to move more than the older animals
breeding vs. over the 7 months that she was followed, moved
an average of 1.4 km between consecutive fixes.
n clumps of Nesting.-The principal nesting area of the
ledges, in American crocodile in Florida is northeastern
r, and in the Florida Bay. Eighty-two percent of all nests
f such areas found in southern Florida from 1970 through
re extremes, 1982 were in this area (Table 2). Maximum num-
erhaps pre- bers of nests found in any yeer were 13 in Flor-
and ponds, ida Bay, 7 on Key Largo, 2 at Turkey Point, and
lary nursery 1 on Cape Sable, for a southern Florida total of
zed by long- 23. It can be expected that ot-her nesting sites
'rents in the and nesting areas exist.


j. rx. , i __ i i Lt%_ A, 4 L, r. j. &ii %4.LU I I





CROCODILE POPULATION BIOLOGY


Skm


FIG. 3. Seasonal distribution of American crocodiles in northeastern Florida Bay. Land areas are stippled,
and dots indicate sightings made during the surveys restricted to the main study area. Winter (non-nesting
season, Dec.-Feb.); Spring (early nesting season, Mar.-May); Summer (late nesting season, Jun.-Aug.); Fall
(post-nesting season, Sept.-Nov.).


We found documentation for 188 clutches of
crocodile eggs in southern Florida since 1930
(Table 3; see Methods for sources). Early data
are scattered, but the number of known nests
increased substantially from the early to late
1970s. In that the number of clutches found
depended on the effort expended in looking for
them, the higher numbers are primarily indic-
ative of greater search effort. However, we note
that the available data cannot support the pro-
posal that an overall decrease in crocodile nest-
ing has taken place in southern Florida (cf. Og-
den, 1978).
Most nests have been found on Key Largo,
Alligator Bay, and Madeira Beach (Table 3); these
account for over half of the known clutches.
Seven of 10 nesting areas were also active his-
torically, in 1930-1950. Reports of nesting near


Alligator Bay go back to 1914, and on Madeira
Beach to 1946. Nesting on Cape Sable and at
Turkey Point has been known only in the last
decade.
American crocodiles nest in spring and sum-
mer in Florida. It is likely that courtship occurs
in late January and February, as is the case for
captive crocodiles in Florida (Moore, 1953; Gar-
rick and Lang, 1977). During this period, croc-
odiles remained in their typical inland habitat
where we saw teiemetered animals together,
indicating that courtship and mating occur in
the mangrove swamps rather than in Florida
Bay. Based on the literature (Lang, 1975; Garrick
and Lang, 1977), it is likely that males maintain
short-term courtship territories within the
broadly-overlapping activity areas.
Crocodiles first visit potential nesting sites in


WINTER


SPRING


SUMMER


FALL

I




I. r. iiLILhd.dA < A.aU t.j. r MALt.U i J'1


FIG. 4. Locations of four adult crocodiles along the northern shore of Florida Bay as determined by radio
telemetry. Dots represent fixes in the non-breeding season; squares represent axes in the breeding season.


mid March, continuing for over a month. We
observed fewer animals, less frequent nest vis-
itation, and delays in initiating nesting during
periods of storms or high winds. Physical evi-
dence suggested that March-April is a period
of nest-site selection. At a site, crocodiles typ-
ically visited, crawled over, and dug at numer-
ous places. Substantial digging began in mid
April, with eggs being laid in late April to May.
Based on clutches for which we had good in-
formation, we estimate that the average laying
date was 5 May (SD = 12.1 days, N = 12). The
average incubation period was 85 days. The av-
erage hatching date was 29 July (SD = 6.7 days,
N = 27 clutches).
A nesting crocodile deposits its eggs in a cav-
ity dug in soil, which is then covered. Nest site
dimensions ranged from a hole 1 x 1 m to a
mound 7 x 5 x 1 m tall. In general, nests were
dug on high ground, in an open area cleared
of vegetation. Open areas ranged from 2 x 3 m
to 10 x 15 m. The nest was placed an average
of 5 m from the water's edge (x = 5.3 m, SD =
4.26 m, N = 20 clutches) but also as far as 17 m
from shore.
Egg deposition sites may be divided into creek


nests and shore nests. The former are on the
raised banks of relatively deep creeks; the latter
are on the beach shores of Florida Bay. Nests
on canal banks at Turkey Point and Key Largo
are analogous to creek nests in natural habitats.
Creek nests appeared to be in more suitable
nesting habitat than did shore nests because
they were located on high, well-drained soil
adjacent to deep (> 1 m) water protected from
the effects of wind and wave action, and within
the habitat used by crocodiles throughout the
year. Nests on beaches fronted shallow water
exposed to wind and wave action. As noted
above, such sites were abandoned by adult croc-
odiles soon after their eggs hatched.
The amount of soil mounding at nest sites
was variable. Although Amercan crocodile nests
have been divided into "hole nests" and "mound
nests" (Campbell, 1972; Ogden, 1978), our data
indicate that there exists a continuum between
the two. The average height of nests measured
was 0.39 m (SD = 0.331, N = 20) We defined a
mound nest as one in which the elevation of
the top of the soil material above the cavity was
higher than the surrounding ground level. By
this criterion we found that 40% (N = 20) of the



































5km
FIG. 5. Activity areas of nine adult and subadult American crocodiles in Florida Bay. Polygons enclose the
activity areas of individual crocodiles as determined by radiotelemetry.


nest sites could be classified as mounds. Some
mounds were relatively permanent and re-
ceived clutches in most years. One well-known
location, called Madeira Mound, may have been
in use since the 1940s and certainly since the
1950s (Campbell, 1972). Variability in nest mor-
phology appears to occur at individual nest sites,
and therefore perhaps among nesting events of
a single individual. At some traditional sites
such as Mud Creek, the clutch was placed in a
hole one year and a mound the next. Not all
mounds constructed in a year received eggs. At
one site with a reworked mound, the clutch of
eggs was laid in a hole in the trail leading to
the nest. It is likely that egg laying takes place
when appropriate substrate conditions are en-
countered irrespective of whether a mound had
developed from the scraping and other explor-
atory activity.
Crocodiles nested in four soil types: sand,
marl, peat, and rocky spoil. The latter two sub-
strates were artificially available on Key Largo
and Turkey Point, respectively. Marl consisted
of very fine soil particles, whereas sand con-
sisted mostly of shell particles (Lutz and Dun-
bar-Cooper, 1984). Marl nests are on natural
creek banks, whereas all sand nests are on beach
ridges along the shore of Florida Bay. In 1980-
1981, we found 14 clutches (64%) in sand and
6 in marl. Sand nests tend to be mounds and


marl nests, holes, but not always. Sand nests
included 10 mounds and 4 hole hests; marl nests
included 2 mounds and 4 holes. Mounds in sand
tended to be larger (f = 0.61 m) than those in
marl substrate (2 = 0.45 m), but the difference
is not significant with the available sample size
(t = 1.49, P > 0.05, N = 10,2).
Communal nesting occurred in Florida Bay.
This conclusion is based on the evidence that
some clutches were laid very close to each other,


TABLE 2. Numbers of clutches of crocodiles locat-
ed in southern Florida (dashes indicate no data avail-
able).

Florida Cape Key Turkey
Year Bay Sable Largo Point Total
1970 5 1 6
1971 10 1 11
1972 10 2 12
1973 10 3 13
1974 7 7
1975 1 1
1977 11 11
1978 12 7 2 21
1979 13 1 5 1 20
1980 12 1 13
1981 9 4 2 15
1982 5 1 4 1 11
Maximum 13 1 7 2 23


vf 0\1U">lJH-. f\^. ^J^/l~ll Ol^L3U1i






TABLE 3. Temporal and geographic distribution of known crocodile nests in southern Florida.

Number of known clutches
Area <1930 1930-1949 1950-1959 1960-1969 1970-1975 1977-1982


Biscayne Bay
Key Largo
Miami Beach
Turkey Point
Florida Bay
Alligator Bay
Black Betsy
Davis Cove
East Florida Bay
Little Madeira Bay
Madeira Beach
Trout Cove
Western Lakes


19
7
8
0
6
13
9
3


as close as 1 m apart in the same mound, and
that in each case the clutches contained eggs of
different sizes. (Egg sizes differ among individ-
ual alligators [Ferguson, 1982].) It also seems
highly unlikely that a single crocodile would
be able to produce two complete clutches with-
in the limited egg-laying period. Thus we be-
lieve that double clutches were from different
females. We found four paired clutches at three
sites in three years. Five large clutches reported
by Ogden (1978) also consisted of two egg clus-
ters each (Lang, pers. comm.). The inference
that Florida Bay crocodiles may nest commun-
ally is also supported by the courtship and egg
deposition patterns of animals in captivity (Gar-
rick and Lang, 1977), and observations in other
locations such as Jamaica and Hispaniola (J. Ot-
tenwalder, pers. comm.).
The average clutch size of crocodiles in south-
ern Florida was 38.0 eggs (SD = 9.45 eggs, N =
46). The smallest clutch we found was 15, the
largest 56. The average clutch size calculated by
Ogden (1978; 44, range = 19-81, N = 20) is
inflated because of the inclusion of five multi-
ple clutches, including nests of 56 eggs in 1971,
of 81, 73, and 78 in 1972 (Ogden, 1978), and of
55 in 1973 (Lang, pers. comm.). We now have
counts of 46 single clutches, including clutches
from 1951, 1967, and 15 from Ogden (1978),
providing an acceptable estimate of clutch size
in southern Florida.
American crocodiles in Florida Bay did not
defend their nest sites against humans. Only
twice did we encounter animals at nest sites,
although physical evidence suggested frequent
visitation by crocodiles through most of the
nesting season. One crocodile encountered at a
nest site did not respond to our presence;
another at a site that did not receive eggs gave
a throaty growl and oriented toward the in-
truder but neither approached nor retreated.


Excessive disturbance of the female at the nest
site caused abandonment of the clutch that year
and changes of site in subsequent years. Only
one of 6 females we captured near but not at
nest sites returned to open her nest that year.
In all cases nest sites near capture locations were
not used the following year. The female pho-
tographed opening her nest by Ogden and Sin-
gletary (1973) and later captured, moved her
nest site the following year (Lang, pers. comm.).
Another female captured at a nest site on one
key was seen at a freshly-mounded site on
another key the next year, although no eggs
were laid where she was found.
The failure of crocodile eggs to hatch was due
to infertility, predation, and embryonic mor-
tality (Table 4). The fertility rate was 90% (281
of 314 eggs were banded). All clutches exam-
ined had fertilities between 84 and 100%, except
for one of 46%. From 1971 to 1982, 14% (14 to
99) of known clutches were depredated by rac-
coons (Procyon lotor). Because predation can call
attention to otherwise overlooked nest sites, the
percentage loss is an overestimate. We found
no predictable pattern of loss among sites, be-
tween shore and creek nests, between mound
and hole nests, or between nests visited by hu-
mans and those not. We believe that the low
density of crocodile nesting inhibited the de-
velopment of nest robbing specialists among
local raccoons, and that nest robbing is a chance
event.
Embryonic mortality, which affected 14% of
all clutches, was caused by either desiccation or
flooding. In the relatively dry summer of 1981,
54 embryos from four cavities failed to hatch.
Each showed signs of excessive water loss, either
the presence of air cavities or incomplete ab-
sorption of yolk sacs (Ferguson, pers. comm.;
Tracy, pers. comm.). Flooding occurred when
ground water entered the egg cavittv (Mazzotti







et al., 1988). We found, by monitoring ground
water level in cavities, that flooding killed one
clutch each in 1980 and 1981 and partially killed
two clutches in 1980. Mortality was nonrandom
between sand and marl nests (x2 = 740, df = 1,
P < 0.01) and between mound and hole nests
(x2 = 8.51, df = 1, P < 0.01), suggesting that
marl and hole nests were more susceptible to
embryonic mortality. All flooding occurred in
hole nests on creek banks.
During 1977-1980, 46 clutches (78.3%) and an
average of 9.4 nests per year hatched some an-
imals. Based on mean clutch size, an average of
357.2 eggs was produced annually. We esti-
mated egg hatching success in 1980 by counting
empty egg shells (an underestimate of hatch-
ing) and subtracting the number of unhatched
eggs from the initial clutch size (an overesti-
mate). Our estimate lies between 42.5% and
72.6% hatching success. Using the midpoint of
the range, 57.5%, we calculate that about 200
(205) eggs hatched per year in northeastern
Florida Bay. This would be an underestimate to
the extent that other nests were undiscovered.
Hatching for the entire population extends
over a period of about one month. In 1980, for
example, hatching dates of nests ranged from
July 23 to August 19 with a mean of August 4
(N = 9 clutches). The earliest hatching dates
known in southern Florida were July 5 and 7,
at Turkey Point (R. Gaby, pers. comm.).
Hatchlings.-American crocodiles open their
nests and assist eggs in hatching (Ogden and
Singletary, 1973), and in Florida Bay the pres-
ence of an adult animal was essential for hatch-
ing. Some eggs were hatched by the adult at
the nest cavity, while others were carried to the
water's edge where hatching took place and the
shells were discarded. Based on the behavior of
other species and our observation that unde-
veloped eggs and dead clutches were not ex-
cavated, we believe that vocalizations initiate
release from the nest cavity. The release of young
by adults is essential to survival because hatch-
lings did not escape from a nest cavity by them-
selves. We found that young partially emerged
from their shell, half unburied, and exposed to
380C temperatures did not complete hatching
on their own and died. In some nests, hatching
was completed on a single night whereas others
were released over several nights.
We have no evidence of parental care by adult
crocodiles after hatching. Despite our hundreds
of person-days of observation, adult crocodiles
were observed near hatchlings only five times.
Three were during daylight, and in each in-
stance the adult crocodile left the area when
discovered. The rapid movement of a teleme-
tered adult female away from her presumed
hatchlings within two days after hatching fur-
ther suggests a lack of parental care.


TABLE 4. Causes or hatching failure in American
crocodile clutches (data from 1971-1974 from Ogden,
1978, with double clutches separated into their com-
ponents).


Year
1971
1972
1973
1974
1977
1978
1979
1980
1981
1982
Total clutches
or mean %


Embryonic
Predation mortality
Number Number
of of
clutches % clutches %
5 50 1 10
0 0 3 30
1 10 0 0
1 14 1 14
S 9 2 18
S 8 1 8
3 23 1 8
S C. 1 8
1 11 2 22
1 20 2 40

14 14 14 24.6


Hatchlings were active at night and inactive
by day. They initially remained together in the
water or on land near their nest site. Micro-
habitats chosen by hatchlings were those hav-
ing the lowest temperatures available (x2, P <
0.05, N = 42). They emerged one-half hour be-
fore sunset, initially remaining near their
groups. Immediately following sunset, we ob-
served them swimming individually between
red mangrove clumps, moving both directions
along the shore and thereby dispersing the
group. We followed one hatchling swimming
vigorously at 10 m/min for approximately 125
m from the nest. By daybreak they returned to
shore.
By following tagged and telemetered hatch-
lings we found that animals from shore nests
dispersed rapidly. At shore nests, hatchlings be-
came displaced during heir nocturnal swim-
ming activity, usually in the direction of long-
shore currents. Movements of hatchlings up to
300 m per day were observed. By two weeks,
some hatchlings from shore nests had moved
inland, eventually entering protected interior
ponds or flooded flats. We found one hatchling
1.6 km from a shore nest / weeks after hatching.
By 7 months, hatchlings had disappeared from
all shore areas.
Hatchlings remained at creek nests for a num-
ber of months. We documented that teleme-
tered hatchlings remained adjacent to their nest
site for up to three weeks, until the transmitters
failed. Tagged hatchlings remained at a creek
nest site 7 months after hatching. We several
times observed hatchlings in a creek, displaced
more than 50 m downstream by the current
during our capture atterrt.s!_mbHk Ihir






previous sites immediately. These observations
support the contention that creeks are the pre-
ferred habitat for young crocodiles, which we
believe to be because they offer substantial cov-
er and protection from wind and wave action.
To test directly the hypothesis that wave ac-
tion determined hatchling habitat use, we ob-
served choice of land or water by 69 hatchlings
1-43 days old in areas having differing wave
action (<5 cm and >5 cm wave height), but
having similar salinity and temperature. We
found that occupancy of land and water habitats
was not independent of wave action (x2 = 38.4,
df = 1, P < 0.05). Hatchlings moved onto land
when wave action was present but remained in
the water when wave action was absent.
Hatchlings remained sedentary, once appro-
priate habitat was found, through the following
spring or longer. We found one 17 month old
crocodile from a shore nest in a creek near
another nest site. Crocodiles on northern Key
Largo have a similar residency period in the
protected habitat there (P. Moler, pers. comm.).
Juveniles disperse from such "nursery" areas
after their first year. One observation may ex-
emplify the typical situation. A crocodile we
tagged at a creek nest on 30 July 1978 was re-
captured 36 months later 13 km away (P. Moler,
pers. comm.). It had entered an area also oc-
cupied by juveniles dispersing from Key Largo,
which had covered similar distances. Inter-
change of young crocodiles also occurred be-
tween Turkey Point and Key Largo (Gaby et al.,
1985). These findings show that juvenile move-
ment is an important mechanism of dispersal
and interchange among nesting areas. Our an-
imal was found because it happened to be in
an accessible location near a major highway,
whereas most dispersing juveniles would not
be seen.
Mortality.-The mortality of juvenile croco-
diles in Florida Bay appears to be relatively high.
However, the causes of mortality remain elu-
sive, as it is difficult to know whether failure
to find hatchlings is due to their death or dis-
persal. It is notoriously difficult to observe ju-
venile crocodilians, especially in such inacces-
sible habitat as mangrove swamp. Nonetheless
we have documented survival of tagged hatch-
lings for 5 months (3 animals), 7 months (1 an-
imal), 17 months (1 animal), and 36 months (1
animal). Documented hatchling survival is very
high on Key Largo, where the nursery sites are
accessible (P. Moler, pers. comm.).
We eventually lost track of all radioteleme-
tered hatchlings, but this did not necessarily
indicate mortality, as the life span of the trans-
mitters was about two weeks. Four transmitters
were recovered without crocodiles. Two were
found intact, knots tied, with no evidence as to


the fate of the hatchling. We suspect that one
of the remaining hatchlings was eaten because
we found holes, probably tooth punctures, in
its transmitter casing. The second transmitter
was found next to the hatchling's skull. A sim-
ilar case of possible predation was observed
during 1980 when a hatchling was tracked to a
land crab (Cardisoma guanhumin) burrow (J. Lang,
pers. comm.) On four occasions we saw blue
crabs (Callinectes sapidis) eating living or dead
hatchling crocodiles. Although a number of po-
tential predators have the ability and probably
the opportunity to eat young crocodiles, the
extent of predation remains undetermined.
Southern Florida crocodiles grow rapidly (our
data suggest a growth rate of 41 cm/yr or 68 cm
TL at 1 yr), which would decrease their suscep-
tibility to predation.
With respect to juvenile and adui: crocodiles,
documented mortality is primarily human-
caused. Of 26 documented deaths in 1971-1983,
all but 6 were related to human activities; 17
deaths were the result of shooting or being hit
by cars (Kushlan, 1988). Of the possible natural
deaths, there was reasonable though circum-
stantial evidence of the death of one subadult
from cold and of another during drought. These
mortality data are biased because unnatural
mortalities were far more likely to be reported
than those from natural causes occurring in in-
accessible locations. Nonetheless, 10 adult an-
imals were known to have died in 12 years,
providing a minimum death rate of 0.8 adults/
yr.
Population Structure.-The proportion of fe-
males in the southern Florida crocodile popu-
lation is 0.67 0.10. This value is not different
from the expected 1:1 ratio (t-test, P > 0.05, two-
tailed). The proportion in Florida Bay was 0.70
females, based on 12 females and 5 males caught
in our indiscriminant capture program. Croc-
odiles captured at Turkey Point included 2 sub-
adult males, 1 adult male, 1 subadult female,
and 3 adult females (R. Gaby, pers. comm.).
Adding these captures to those from Florida Bay
brings the total to sixteen females to eight males
captured in southern Florida. The small sample
size and possible bias in capturing males rein-
force the conservative position that the sex ratio
is not different fro,:n 1:1.
We found all expected size classes in the
southern Florida crocodile population during
surveys and capture programs (Fig. 6). Lacking
information on growth rates for all but hatch-
lings, it is not possible to construct a detailed
age-class distribution for southern Florida croc-
odiles. However, we can define three age groups
hatchlingg, juvenile, adult) bv size; the Florida
Bay population is distribued across all three
age categories (77% hatchling, lb% juveniles, 6%






adults). The size structure of the breeding fe-
males appears well distributed, with a 1:3:1 ratio
among crocodiles in the 2.25-2.5, >2.5 < 3.0,
and >3.0 m TL size classes.
The age categories were determined as fol-
lows: (1) crocodiles less than 0.5 m total length
are in their first 6 months of life and are con-
sidered hatchlings; (2) juveniles were from 0.5
m to the size at first breeding, 2.25 m; (3) adults
were larger than the size at first breeding, which
was determined through several lines of evi-
dence. Female crocodiles associated with spe-
cific nest sites during the nesting season were
2.28, 2.47, 2.57, 2.59, 2.96, and 3.08 m TL. All
but one, captured in early April, had distended
cloacae when captured, indicating breeding
(Webb, pers. comm.). In 1981, a small female,
2.28 m TL, was captured at a nest site that had
not been used previously, suggesting that it may
have been her first breeding attempt. LeBuff
(1957) reported nesting in captivity by croco-
diles 7-9 ft TL (2.1-2.7 m, but probably mea-
sured only to the nearest 1 foot). We assume
males are capable of mating at the same size as
females.
The largest crocodiles captured in Florida Bay
were around 3 m TL. The largest female cap-
tured was 308.0 cm TL (166.5 cm SV); the largest
male was 289.3 cm TL (147.5 cm SV). On surveys
we made 10 sightings of animals we placed in
the 3 m class (class center, 25 cm intervals), and
one in the 3.5 m class. Males grow larger. We
handled a male at Turkey Point that was 3.75
m TL and a captive male originally from Jamaica
that was 3.95 m TL. Our 3 m long female may
have been postreproductive when she died of
undetermined causes in 1979 in that the eggs
laid at the site which she frequented failed to
develop in 1977 and 1979 (they were eaten by
raccoons in 1978).
Population Size. -Using Chabreck's model, we
calculate that 90 32 adult and juvenile croc-
odiles occurred in our study area and 130 46
in Florida Bay. Adding the number of hatch-
lings we calculated previously, we estimate a
maximum population after hatching of 330
crocodiles in Florida Bay.
To calculate the variables in Chabreck's for-
mula we used survey, capture, and nesting data
from our study area in northeastern Florida Bay.
The maximum nesting effort (N) was 13 nests
in the study area in 1979. The sex ratio (F) was
0.67 0.10. The percentage of females nesting
(E) was 0.72 0.09 (the maximum number of
nests, 13, divided by our minimum estimate of
the adult female population, 18, which includ-
ed the 13 females we captured plus the 5 nest
sites at which we did not capture a female). The
proportion of adults (A) was 0.30 0.06 (the
number of adults captured, divided by the total


20 r


0
w4
>
zW
0
0


SURVEYS


10


. m I n1 n [l n F
0.50 0 75 1.00 1.25 1.0S 1.75 2.00 2.25 2.50 2.75
20 -

CAPTURES
10 -



0S0 0.75 1.00 1.25 50 1.75 2.00 225 2.50 2 75 300
SIZE CLASS, m


FIG. 6. Size distribution of American crocodiles in
southern Florida. To avoid bias these data do not in-
clude 369 animals <0.5 m TL captured in concen-
trated efforts at nests. There was no difference in the
size frequency distributions of crocodiles observed
on surveys or captured (U-test, P > 0.05).

number of non-hatchling crocodiles captured).
Because 69% of all animals tallied on standard
surveys were observed in our study area we
were able to extrapolate the number in our study
area to all of Florida Bay by multiplying by 1.45.
We estimate that the total population of adult
and juvenile crocodiles in southern Florida is
220 78 (or between about 150 and 300) ani-
mals. After hatching, the total population would
on average be over 500 animals. To estimate the
total southern Florida population, we assumed
that parameters we calculated for Florida Bay
hold elsewhere and that the number of animals
in Florida Bay is proportional to the percentage
of nests there (24/13 = 1.69). Thus to extrapo-
late, we multiplied our Florida Bay population
estimate by 1.69.
The approximately 220 adult and juvenile
crocodiles are distributed as follows: 130 near
Florida Bay, 70 on northern Key Largo, and 20
at Turkey Point. The latter estimate compares
well with the 19 estimated by Gaby et al. (1985).
A few additional animals may be expected pe-
riodically elsewhere in the overall Florida range
(Kushlan and Mazzotti, 1989).
Introductions.-We have found 15 instances of
American crocodiles being released in southern
Florida, involving about 45 animals over 17 years
(see also Behler, 1978). Seven of these releases
involve animals known or suspected to be for-
eign to the resident Florida population. Only 4
of these animals were released in northeastern
Florida Bay, the rest having been released near
Cape Sable. Most releases weie by Federal or
state officials in cooperation with zoos or animal
attractions seeking to dispose of specimens. Six
animals were adults when released; 20 were
hatchlings from Panama. Because none was per-
manently and distinctively marked, there is no






way of knowing whether these animals sur-
vived.

DISCUSSION
Habitat.-On the basis of the results of this
study, we can now summarize the habitat pref-
erence of the American crocodile in Florida. Its
overall distribution and probably its nesting
range appear to be determined by the distri-
bution of relatively warm winter temperatures
(Kushlan and Mazzotti, 1989). Within this range,
crocodiles appear to frequent protected coastal
areas, particularly mangrove-lined coastal creeks
and ponds off Florida Bay and similar artificial
habitat on northern Key Largo and at Turkey
Point. Crocodiles use the open water of Florida
Bay only in transit to nest sites.
These results indicate that the American croc-
odile is an estuarine species, not a marine one
(cf. Barbour, 1923; Moore, 1953; Ogden, 1978),
a view supported by Dunson's (1982) demon-
stration that hatchlings grow faster in brackish
water than in either fresh or saline water. We
suggest that an important aspect of their oc-
cupancy of mangrove swamps is the avoidance
of wind and wave action, as has also been re-
ported for other crocodilians (Graham, 1968).
It appears that the salinity of water in Florida
Bay does not adversely affect crocodiles, be-
cause both adults and hatchlings are able to
compensate for high salinity, physiologically
and behaviorally, and especially because they
do not live in saline water permanently. Al-
though early laboratory studies (Dunson, 1970;
Evans and Ellis, 1977) demonstrated that hatch-
ling crocodiles should not be able to survive in
the salinity of water found near nest sites, sub-
sequent studies conducted in collaboration with
our own revealed behavioral adaptations to high
salinity that include eating hydrated prey,
drinking fresh water, avoiding salt intake even
in relatively high salinity, and a body mass ef-
fect (Dunson, 1982). American crocodiles also
possess salt glands (Taplin et al., 1982), al-
though their function remains in dispute (G.
Grigg and W. Dunson, pers. comm.).
A second aspect of habitat choice is the use
of sites for nesting. High-ground marl banks
and sand beaches occur in limited numbers, but
their overall extent and the ability of crocodiles
to nest communally indicate that nesting hab-
itat is not limited in Florida Bay.
Sociality.-Based on the use of large, overlap-
ping activity areas, our frequent observation of
animals together, and evidence for communal
nesting, we suggest that the American crocodile
is a social species. This conclusion is supported
by studies of captive animals, whose behavior
included a substantial social component (Gar-


rick and Lang, 1977). They concluded that the
American crocodile was more social than the
American alligator (Alligator mississippiensis).
Nesting.-Nesting phenology of the Ameri-
can crocodile in southern Florida is in concert
with local hydrologic and temperature cycles.
Nesting begins after the cold weather of winter,
near the end of the dry season, and ends prior
to the highest water levels of the wet season.
Highest rainfall and lowest salinities of the year
occur in the post-hatching period. Thus the in-
cubation period avoids both the low tempera-
ture of winter and high temperatures of late
summer. This timing tempers the effects of the
twin perils to incubating eggs, desiccation and
flooding (Lutz and Dunbar-Cooper, 1984; Maz-
zotti et al., 1988).
The timing of nesting in the American croc-
odile differs in various parts of its range. Croc-
odiles nest at the same time in Florida as in
Venezuela, Mexico, and Honduras, but they nest
in December-February in Ecuador and Panama
(Schmidt, 1924; Rand, 1968; Medem, 1973; Al-
varez del Toro, 1974). American crocodiles from
Jamaica maintained near Lake Okeechobee,
Florida, nested several weeks before Florida Bay
animals (J. Lang, pers. comm.); and captive Flor-
ida crocodiles at Bonita Springs laid eggs from
mid March to mid May (Moore, 1953). It is likely
that initiation of the nesting season is in part
temperature-related, gametogenesis undoubt-
edly being inhibited in cold temperature.
The variation found in the nest sites of the
American crocodile in Florida Bay supports none
of the theories proposed to account for croco-
dilian nest structure. It has been postulated that
nest structure has a phylogenetic basis in which
hole nesting is a primitive characteristic (Greer,
1970). However, the American crocodile has
been described both as a hole-nester and as a
mound-nester (Schmidt, 1924; Greer, 1970; Neill,
1971; Campbell, 1972; Ogden, 1978). Our mea-
surements confirm these observations. Webb et
al. (1983) suggested that mouncs occur in species
that nest during wet seasons or in marshes. Neill
(1971) suggested that the compactness of the
substrate determined whether a nest was a hole
or a mound. Our observations suggest that
whether a clutch is placed in a mound depends
on the individual animal and on its finding an
appropriate substrate for the clutch. The exis-
tence of a mound is not related to substrate.
Moreover, we found no statistical difference in
the mean size of mounds in marl and sand.
Nonetheless, the largest mounds were made of
sand. It seems likely that the mound nests of
the American crocodile are not homologous to
those of other mound building crocodiles who
invariably construct mounds of vegetation.







Hatchlings.--Most crocodilians defend their
nest and hatchlings (Cott, 1971; Kushlan, 1973;
Alvarez del Toro, 1974; Hunt, 1975; Kushlan
and Kushlan, 1979). Our failure to observe nest
defense, pod formation, or hatchling defense is
atypical, even for American crocodiles in cap-
tivity and in other locations (Alvarez del Toro,
1974; Dugan et al., 1981). Ogden and Singletary
(1973) documented nest opening, egg opening,
and transport of young in the mouth by adult
American crocodiles in Florida Bay, and we
found that such parental assistance in hatching
nests is essential to hatchling survival. The rea-
son for lack of parental behavior after hatching
is unclear. It is possible that a past history of
human disturbance has eliminated guarding
behavior from the local population. Alligators
guard nests primarily in areas free from ha-
rassment (Kushlan and Kushlan, 1979). Alter-
natively, limited parental care may be a long-
standing, intrinsic characteristic of crocodiles
in Florida.
Juvenile crocodiles may remain at suitable
"nursery" sites for a year or more, but all evi-
dence suggests that dispersal occurs in the sec-
ond year. Such dispersal is characteristic of many
crocodilians (Webb and Messel, 1978; Messel et
al., 1980). However, in Panama Rhodda (1984)
found American crocodiles 10 and 22 months
old occupying small activity areas near their
nest site. Thus the amount and extent of dis-
persal may differ among populations.
The age distribution of Florida Bay crocodiles
demonstrates that long-term recruitment is oc-
curring. That the proportion of juveniles found
was somewhat smaller than might be expected
in a stable population could reflect either high
hatchling mortality or the underrepresentation
of subadults in capture and survey data. The
latter is probably the case in that such under-
representation is found in most crocodilian
studies (T. Joanen and H. Messel, pers. comm.).
Rapid growth rates also provide a quick passage
through the smaller size classes. Furthermore,
concurrent studies in southern Florida have
demonstrated that hatchling survival is rela-
tively high. Moler (pers. comm.) reported sur-
vivorship of 50% of tagged hatchlings in 1 yr
in the protected habitats of northern Key Largo,
and Bohnsack (pers. comm.) reported survivor-
ship at Turkey Point for 7 years of 5% of hatch-
lings tagged in 1978 and 15% of hatchlings
tagged in 1979 (see also Gaby et al., 1985). Gra-
ham (1968) stated that theoretically a crocodile
population could remain stable despite a hatch-
ling mortality of 99%.
Population Size.-Our estimate of about 220
animals represents a small but potentially via-
ble population. We were able to calculate this


estimate from population parameters of the
study population. Previous estimates have been
based on data from other species or on assump-
tions unsecured by data. Ogden (1978) estimat-
ed the population to be 400-500 animals based
on alligator and Nile crocodile data parameters
and assumptions as to female proportions and
number of nest sites (Chabreck, 1966; Cott, 1971).
Ogden (1978) also applied estimates of mortal-
ity and age at maturity to predict a population
of 100-400 crocodiles, excluding hatchlings.
We do not believe that there is sufficient in-
formation on which to base any estimate of pop-
ulation size prior to human settlement of south-
ern Florida. Ogden (1978) interpreted the
writings of explorers and crocodile hunters to
indicate that they were able to see "a few crocs
per day (< 10)." Contrasting that with his more
recent experience, he guessed that "the number
of crocodiles in south Florida at the end of the
19th Century was not more than five times the
present population, probably between 1,000 and
2,000 animals" (Ogden, 1978, p. 192). Even to-
day, however, one can expect to see at least a
few crocodiles per night in areas where they
occur, a situation not very different from that
reported historically.
By the 1940s it was thought that the number
of crocodiles in southern Florida had been
greatly reduced from historic numbers (Beard,
1938; Carr, 1940; Allen and Neill, 1949; Dick-
inson, 1953). However, again, little actual in-
formation exists from the 1940s on which to
base such an impression. Crocodiles, like other
wildlife, certainly were hunted by early settlers
and probably before that by Indians (Smith,
1896). Settlement of Biscayne Bay began by the
1870s, so that even before 1900 crocodiles were
probably killed there. Documentable hunting
was usually for museum or zoo specimens. A
decrease in crocodiles may have been initiated
by hunting, but habitat loss to development of
Miami Beach, Miami, and the Florida Keys was
the ultimate cause of changes in the nesting
distribution (Kushlan ard Mazzotti, 1989). De-
spite any early reductions we can conclude
crocodiles were not uncommon in northeast
Florida Bay and south Biscayne Bay through the
early 1950s, but we can have no idea in what
numbers they occurred.
The Florida population ut the American croc-
odile clearly is small, restricted to the barely
tropical tip of the Florida peninsula, and iso-
lated from other such populations. What seems
remarkable to us is not so much the small size
of the population but its demonstrated ability
to persist in the face of the intensive human
occupancy of southern Florida. Its population
characteristics fail to suggest any inherent in-






stability (Kushlan, 1988). However, such a small
and restricted population is potentially at risk
to the vagaries of random processes and cata-
strophic events, a situation not atypical of any
rare species on the periphery of its range.

Acknowledgments.-We thank our colleagues
in the study of Florida crocodiles John Behler,
William Dunson, Tamir Ellis, David Evans, Ron-
ald Gaby, Richard Klukas, Jeffrey Lang, Peter
Lutz, Paul Moler, Joseph Moore, John Ogden,
Daniel Stoneburner, and William Robertson, Jr.
We thank also those who assisted in the field,
especially Robert Austin, Joanna Booser, Linda
Campbell, Carol Hewes, Terri Jacobsen, Debo-
rah Jensen, Lori Lagna, Amanda Muller, Paige
Patty, Mark Salzburg, and Ron Wideman. We
also thank, for their valuable criticisms and ad-
vice, I. Lehr Brisbin, the late Howard Campbell,
William Dunson, Ronald Gaby, Les Garrick, Ted
Joanen, Jeffrey Lang, William Magnusson, Har-
ry Messel, and Grahame Webb. I thank an anon-
ymous reviewer for making a number of im-
portant suggestions regarding presentation and
analysis. This study was funded by the National
Park Service, in cooperation with the U.S. Fish
and Wildlife Service, Florida Game and Fresh
Water Fish Commission, Florida Power and
Light Co., Connell Associates Inc., the National
Science Foundation, Pennsylvania State Uni-
versity, University of Miami, New York Zoo-
logical Society, University of Georgia Institute
of Ecology, and Nova University.


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Accepted: 12 November 1987.




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