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DISTRIBUTION AND POPULATION ECOLOGY
OF THE FOX SQUIRREL IN FLORIDA
By
JOHN BRUCE WOODING
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
1997
.D
780
99J
UNIVERSITY OF FLORIDA
3 1262 08552 4584
ACKNOWLEDGEMENTS
I conducted the field work on this project while employed as
a wildlife biologist with the Florida Game and Fresh Water Fish
Commission. The work was fully funded by the Commission, and I
appreciate the Agency's permission to use their data for this
dissertation.
Many people who work for the Commission assisted with the
project. Special thanks go to Tom Logan, Brad Gruver, Jim Brady,
Paul Moler, and Tim Breault. Help with the field work was
provided by many people, including Mark Cantrell, Dee Hungerford,
Don Coyner, Bill Frankenberger, Brett Kempker, Patricia McNeill,
and Vic Doig. Jeff Hamblen helped with mapping and graphics, and
Steve Linda assisted with the statistical analysis.
A portion of the field work was conducted on property
managed by the Florida Department of Environmental Protection.
Jim Stevenson of that agency was particularly facilitative.
Field work on the Fort White study area was conducted on
privately owned property. The landowners graciously allowed me
access and permission to study the fox squirrels living on their
farms. Special thanks go to Billy Cason, Tom Fowler, and the
Gray Shadow Ranch.
My graduate committee at the University of Florida has been
demanding. I have prospered from their demands, and I appreciate
their commitment to quality. Steve Humphrey has been helpful
during all aspects of the process.
I also thank the administrative staff at the University.
This includes Cathy Ritchie, Shannon Stull, Mindy Edwards, and
Cynthia Sain. I also thank the fine people working in the
Graduate School. On the numerous occasions when I've done
something incorrectly (one must follow the rules without
exception, no matter how trivial one believes them to be), they
have helped me straighten out the mess--and they have always done
it with a smile (sometimes with a strained smile, but a smile
nonetheless).
On the home front, my family has been cheering me on
throughout the project. From the bottom of my heart, I thank
you.
iii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ............................................ ii
A BSTRA CT ................... ................................ v
CHAPTERS
1 INTRODUCTION ...... ........ ............................. 1
Background Information on Fox Squirrels ................ 2
2 DISTRIBUTION ...... ........ ............................. 7
Methods ..................................... ... ....... 8
Results and Discussion................................ .. 9
3 POPULATION ECOLOGY..................................... 34
Study Areas ............................................. 35
Me thods ................................................ 38
Results and Discussion ................................. 44
Concluding Discussion.................................. 85
4 REINTRODUCTION..... ......... ........................... 98
Methods ...... ........................................ 99
Results and Discussion ................................. 100
5 CONSPECIFIC ATTRACTION... ............................... 107
6 FUTURE OF FOX SQUIRRELS................................ 116
7 SUMMARY AND CONCLUSION ................................. 127
LITERATURE CITED................................................. 132
BIOGRAPHICAL SKETCH......................................... 139
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
DISTRIBUTION AND POPULATION ECOLOGY
OF THE FOX SQUIRREL IN FLORIDA
By
John Bruce Wooding
August 1997
Chairman: Stephen R. Humphrey
Major Department: Wildlife Ecology and Conservation
Fox squirrel (Sciurus niger) distribution, movements,
demographics, and management were investigated in Florida from
1989 to 1995. Fox squirrels were determined to be widespread in
Florida, occurring in 65 of the state's 67 counties. There were
no reported occurrences for Dade and Broward counties. The
distribution, however, was patchy due to habitat loss. The
largest expanses of fox squirrel habitat were found on public
lands in northern Florida.
Fox squirrel movements and demographics were studied on two
areas in northern Florida. Forty-four fox squirrels were
monitored during the study. The density of fox squirrels on one
study area was 7.4 fox squirrels/km2; the density on the second
area was 11.7 fox squirrels/km2. Male home ranges overlapped
extensively with those of females and other males, but there was
little overlap in home ranges of adult females. Eight of 15 fox
squirrels collared as subadults dispersed. Two older fox
squirrels also dispersed. Dispersal distances ranged from 1.0 to
7.2 km. The annual mortality rate for the radio collared animals
was estimated at 27-30%. Litter size ranged from 1-3.
Populations had two breeding seasons per year, but the litter
frequency of radio-collared females was 1.07 litters per year.
Six radio-collared fox squirrels were translocated in 1995
to establish a breeding population in a state park. The radio
signal was lost on one squirrel while it was still on the park,
but the other 5 animals left the park following their release,
indicating that the habitat on the park was unacceptable to fox
squirrels. Dispersing squirrels settled where neighboring
populations occurred, showing that local sources of fox squirrels
were available that could naturally colonize the park. Further
relocation of fox squirrels to the area was unwarranted under the
current conditions.
CHAPTER 1
INTRODUCTION
Five hundred years ago, Florida was a wilderness.
Today, it is a world famous center of urban and agricultural
development. Florida's human population reached 14 million in
1995, and the population is expected to increase to 20 million by
2020 (Floyd et al. 1996). Many species of wild animals that were
adapted to the Florida wilderness have declined in abundance due
to the state's development (Cox et al. 1994). The fox squirrel
(Sciurus niger) is one of those species.
This dissertation contains the results of an observational
study on the fox squirrel in Florida. The intention of the work
was to gather basic information on distribution and biology that
could be applied to conserve the species. This was not a study
of the theoretical or mathematical aspects of wildlife ecology.
My goals for the dissertation were to present a tightly written
report that contained the data I collected. Chapter 1 contains
an overview on fox squirrels and it is offered as background
information for the chapters that follow. The next three
chapters contain the data collected in the study. Chapter 2
contains information on fox squirrel distribution in Florida,
Chapter 3 contains information on the population ecology of fox
squirrels in northeastern Florida as determined using radio
telemetry methods, and Chapter 4 contains the results of an
effort to restock fox squirrels into a state preserve.
2
My intentions were to keep the discussion to a bare minimum,
something which I appreciate in technical reports written by
others. However, dissertations are an academic exercise. I
hence expanded the scope and included two discussion chapters.
Chapter 5 contains a discussion on conspecific attraction and the
influence this behavior has on patterns of animal distribution
and conservation of populations in fragmented habitat. Chapter 6
contains a discussion on the future of fox squirrels in Florida.
Background Information on Fox Squirrels
The remainder of this chapter presents a review of fox
squirrel life history and status and an overview of prior
research conducted on the species. This information is offered
as background for the chapters that follow.
Fox squirrels occur in most of the eastern and central
portions of the United States (Koprowski 1994), and their range
extends into south-central Canada. Fox squirrels have been
introduced into California, Oregon, and Washington (Flyger and
Gates 1982).
Fox squirrels are large tree squirrels (Silva and Downing
1995). Body mass can exceed 1.3 kg (Flyger and Gates 1982).
Pelage colors range from a grizzled gray tinged with orange in
the midwestern United States to black, silver, or khaki in the
southeastern United States. Fox squirrels in the southeastern
Coastal Plain usually have white ears and muzzles. Individuals
can be a mix of colors. I have seen fox squirrels in Florida
with black faces, white ears and muzzles, black shoulders and
front legs, chestnut brown backs, tan flanks, and burnt orange
tails. All are not this colorful, but the most colorful are
striking animals.
Taxonomy
Fox squirrels are one of the world's 28 species of tree
squirrels (Wilson and Reeder 1993). The genus Sciurus occurs
throughout Europe, northern Asia, and North and South America
(Nowak 1991). One species occurs in Japan (Wilson and Reeder
1993).
Hall (1981) recognized 10 subspecies of fox squirrel. Four
of these occur in Florida: S.n. avicennia (Big Cypress fox
squirrel), S.n. bachmani (Bachman's fox squirrel), S.n. shermani
(Sherman's fox squirrel), and S.n. niger (Southeastern fox
squirrel). The taxonomy of fox squirrels in the southeast was
recently reviewed by Turner and Laerm (1993). They concluded
that S.n. bachmani was not distinct enough to warrant recognition
as a separate subspecies. In their opinion, S.n. bachmani, was
only a clinal variation of S.n. niger. S.n. shermani and S.n.
avicennia, however, were considered distinct subspecies.
The three subspecies that Turner and Laerm (1993) recognized
for Florida (S.n. avicennia, S.n. shermani, and S.n. niger)
differed primarily in body size: S.n. avicennia was the smallest,
S.n. niger was intermediate in size, and S.n. shermani was the
largest. Pelage patterns were used by Moore (1956) to help
distinguish the different subspecies in Florida, but Turner and
Laerm (1993) found that pelage was too subjective and varied for
use as an indicator of taxonomy.
Legal Status in Florida
The Big Cypress fox squirrel is the only subspecies endemic
to Florida (Turner and Laerm 1993). It occurs only in the extreme
southwestern portion of the state and is listed by the Florida
Game and Fresh Water Fish Commission (GFC) as a threatened
species. Sherman's fox squirrel occurs throughout the peninsula
and panhandle west to Okaloosa County. It also occurs in central
and southern Georgia. It is considered a species of special
concern by the Florida GFC. The southeastern fox squirrel only
occurs in Florida in the western panhandle, but its range outside
of Florida extends over much of Alabama, northern Georgia, South
Carolina, and North Carolina (Turner and Laerm 1993). It is not
listed.
Fox squirrels were formerly game animals in Florida, and
legally hunted statewide. The season was closed in stages,
beginning first in south Florida within the range of the Big
Cypress fox squirrel. The season closed there in 1972. Next,
the season was closed on all wildlife management areas in 1991.
Fox squirrels were then legal game only on privately owned land
in central and northern Florida. The season there ended in 1995.
The final closure ended all legal hunting of fox squirrels in
Florida.
Previous Studies
Fox squirrel research specific to Florida was begun in the
1950s by Moore (1956, 1957), who focused his attention on
distribution, taxonomy, and life history. Status surveys were
conducted in the 1970s by Brady (1977) and Williams and Humphrey
(1979). In the late 1980s, Kantola and Humphrey (1990)
investigated habitat use of radio-collared fox squirrels in
northern Florida. A study of urban fox squirrels in southwestern
Florida was completed in the early 1990s by Jodice and Humphrey
(1992).
There have been several studies of fox squirrels in other
southeastern states. In Maryland, Taylor (1973), Lustig and
Flyger (1975), Dueser et al. (1988), and Larson (1990) examined
the status and habitat requirements of the Federally endangered
Delmarva fox squirrel (S.n. cinereus). In North Carolina, Weigl
et al. (1989) conducted an 8-year study on fox squirrel
population biology and habitat requirements. In South Carolina,
Wood and Davis (1981) and Wood (1985a,b) investigated status and
human perceptions of fox squirrels, and Edwards (1986) studied
habitat selection by radio-collared fox squirrels. In Georgia,
Hilliard (1979) also conducted a study of fox squirrels using
radio-telemetry techniques. A similar study was completed in
southern Alabama by Powers (1993).
Research on fox squirrels in the midwestern United States
has been more extensive than that completed in the southeast.
The first midwestern studies were completed in the 1940s (Allen
1943, Baumgartner 1943, Brown and Yeager 1945). These first
studies focused on life history, habitat requirements, and
management of fox squirrels as a small game species. More recent
studies of midwestern fox squirrels have built on the earlier
work. These include studies of behavior (Benson 1980, Koprowski
1993), food habits (Korschgen 1981, Nixon et al. 1968), ageing
techniques (McCloskey 1977), and habitat management (Nixon and
Hansen 1987).
6
There have been several general reviews of fox squirrel
research and biology. Flyger and Gates (1982) and Koprowski
(1994) reviewed the literature on fox squirrels for the species
entire range. Weigl et al. (1989) and Loeb and Moncrief (1993)
focused their literature review on fox squirrels in the
southeastern United States. Kantola (1992) and Humphrey (1992)
reviewed the biology and status of fox squirrels in Florida. A
review of the biology of all species of tree squirrels was
completed by Gurnell (1987).
CHAPTER 2
DISTRIBUTION
Two previous surveys assessed the distribution of fox
squirrels in Florida. Brady (1977) used a mail survey of
wildlife experts to determine the state-wide distribution of fox
squirrels. He found that the species occurred throughout the
state but the distribution was patchy. He identified several
areas where there were large concentrations of habitat and where
fox squirrels were considered common, but overall, the species
was uncommon as a consequence of habitat loss. The second survey
was restricted to southern Florida, within the range of the Big
Cypress fox squirrel (Williams and Humphrey 1979). They
determined through personal interviews that fox squirrels were
present but rare in Lee, Hendry, Collier, and northern Monroe
Counties
In 1989, I attempted to update the statewide survey
completed by Brady (1977). To accomplish this, 437
questionnaires were mailed to field personnel employed by the
Florida Game and Fresh Water Fish Commission. Respondents were
provided a blank map of Florida on letter sized paper. The map
showed county borders and respondents were asked to mark specific
locations where populations of fox squirrels occurred. Of the
437 surveys mailed, 183 were returned. Upon review of the
surveys, it was decided the information mapped was not precise
enough to assess the current distribution. This was in part a
fault of the small scale map mailed with the survey. It was also
perhaps due to unclear instructions.
After going back to the drawing board, considering that time
and manpower were limited, it was decided that personal
interviews would be used to determine distribution and status.
The information gathered from the interviews is presented in this
chapter.
Methods
First, a GFC field employee who would serve as a local
expert was identified for each of Florida's 67 counties. These
people were selected by contacting regional supervisors and
others in the Agency who knew which person was the best contact
for each county. Criteria used in the selection included the
person's time in the county and their level of knowledge. The
selected employees included wildlife officers, wildlife
biologists, and wildlife technicians.
These people were interviewed in person in the county of
interest. The interviews were conducted while looking at a
Department of Transportation county map. Each respondent was
asked to share their knowledge of fox squirrel distribution and
abundance in the county. Counties were examined by quarters
(northeast, northwest, etc.) to keep the respondent focused. The
distribution information was marked on the map as the interview
progressed.
After the distribution data was mapped, the respondent was
asked to drive the interviewer to specific locations in the
county where fox squirrels occurred. The on-site visits allowed
the interviewer to observe first-hand the characteristics of the
habitat occupied. The intent was to make general observations on
the habitat such as dominant plant species, vegetation structure,
and land uses. Land-owners and managers encountered during the
field trips were asked general questions about fox squirrels.
A county survey was normally completed in one day. However,
if the respondent was unfamiliar with portions of the county,
they were asked for the names and phone numbers of people who
knew the area in more detail. These other people were contacted
by telephone and asked to share their knowledge of fox squirrel
distribution and abundance in the portion of the county in
question. The information they provided was added to the county
maps used in the field.
A crude estimate of habitat quantity for the larger
populations was made using the section grid on the county maps.
These estimates were used to assign the populations to one of
three size categories: small (<1,000 ha); medium (1,000-4,000
ha); or large (4,000 ha). These estimates were only ball park
approximations based on the information mapped, and they are
presented with that caution in mind.
Results and Discussion
Distribution
Fox squirrels were widely distributed in Florida, but the
distribution was patchy. Similar conclusions were reached by
.Brady (1977) and Williams and Humphrey (1979).
Fox squirrels were reported to occur in 65 of Florida's 67
counties (Table 1). There were no squirrels reported for Dade
and Broward counties, although there was a possibility they
occurred in the extreme western portion of both counties. They
were reported to occur there in the earlier Florida surveys
(Brady 1977, Williams and Humphrey 1979), and while the habitat
still existed when the current survey was conducted, none of the
people interviewed had seen fox squirrels in either county.
Other than the difference noted above, there were no
indications from the data that there had been major changes in
fox squirrel distribution in the years between the surveys. As
will be discussed later, there have been changes in the quantity
of fox squirrel habitat in Florida in recent years, and from that
it seems reasonable to conclude that fox squirrels have declined
in abundance, but the survey data did not detect those changes.
Largest Populations
The largest populations identified in the surveys are listed
by county in Table 1. Several of the populations occurred in
habitat that crossed county lines. If the habitat was under the
control of one agency or landowner, it was counted as one fox
squirrel population for the discussions that follow. As an
example, the fox squirrels living in Apalachicola National Forest
were considered one population, although the forest lies in three
counties.
There were 59 large fox squirrel populations in Florida.
Eight of the 59 populations occurred in areas were the quantity
of habitat was estimated to exceed 4,000 ha. These were the
largest populations in the state. Two of the largest areas were
military bases (Eglin and Camp Blanding), two were National
Forests (Apalachicola and Ocala), and two were State Forests
(Blackwater and Withlacoochee). The habitat on these areas
consisted primarily of longleaf pine (Pinus palustris) sandhill,
except that on Apalachicola a large portion of the habitat was
longleaf flatwoods. The forests on these areas were generally
managed for timber production, and the understory vegetation was
controlled by prescribed fire. Camp Blanding, which appeared to
have the poorest quality habitat of the six major areas on public
land, contained vast areas of cut-over sandhills that were
dominated by turkey oak (Quercus laevis) thickets. The thickets
were believed a consequence of over-logging of pines and fire
suppression. My impressions were that most of the habitat on
Blanding was marginal as a result of the management. However,
Blanding is now under a different management approach, and the
habitat for fox squirrels should improve.
The two other large populations in Florida occurred on
private land. One of these occurred on the quail (Colinus
vircinianus) plantations that dominate the landscape in northern
Leon and northern Jefferson Counties. The habitat on the
plantations consisted of mature stands of longleaf, loblolly (P.
taeda), and shortleaf pine (P. echinata), interspersed with corn
(Zea mays) fields and food plots of various legumes planted for
quail. My impressions were that the habitat was the richest in
the state in terms of food abundance, partially due to quail
management activities, but also due to the natural fertility of
the clay soils. These soils contrast with the nutrient poor
sands that characterize most of Florida's upland soils.
The second large area of privately owned habitat occurred in
Osceola, Indian River, and Brevard counties, east of Kenansville
and west of the St. Johns River. The area contained a series of
neighboring ranches which managed their properties for cattle and
wildlife. The habitat on the ranches consisted of xeric
flatwoods with mature pines, scattered live oak (Q.
virginian)/cabbage palm (Sabal palmetto) hammocks, and forested
creek strands. Several of the ranches maintained feeding
stations for wildlife, and I was told that fox squirrels were
often seen at the feeders. My impressions were that this area
contained one of the densest populations of fox squirrels in the
state.
In addition to the eight large populations, there were 32
populations that were classified as medium-size (1,000 4,000 ha
of habitat). Twenty one of these populations were on land
privately owned. Sixteen of these occurred on ranches managed
for cattle production. The habitat on the ranches consisted
primarily of live oak/cabbage palm hammocks, patches of xeric
longleaf and slash pine (P. elliotti) flatwoods, longleaf
sandhill, and forested fencerows and strips of hardwoods along
creeks and drainages. The understory on the ranches was kept low
by a combination of grazing, prescribed fire, and mowing.
However, in south Florida, in spite of these activities, much of
the understory vegetation consisted of dense stands of saw-
palmetto (Serenoa repens).
Of the other five medium-sized populations on private land,
two occurred on land managed for timber, two occurred on quail
plantations, and one occurred in a slowly developing residential
area located in sandhill.
Eleven of the 32 medium-sized populations in the state
occurred on publicly owned property. Seven of these were on
state lands managed for a variety of purposes. Four were managed
as wildlife management areas (Cecil Webb, Joe Budd, Apalachee,
and Three Lakes), one as a state park (Wekiva and surrounding
state lands), one as a state forest (Jennings), and one as a
nature reserve and research center (K. Ordway). The habitat on
the areas varied from primarily longleaf sandhills for the five
areas in northern Florida to xeric flatwoods and live oak
hammocks for the two areas in southern Florida. The understory
vegetation was managed by prescribed fire, and in addition, by
cattle grazing on the two areas in southern Florida.
The other four medium populations on public lands occurred
on Federally owned property. Two of these were military bases
(Cecil Field and Avon Park), one was a national forest (Osceola),
and one was a national wildlife refuge (St Marks, Panacea Unit).
The habitat on these areas was primarily xeric, longleaf
flatwoods. The habitat on Avon Park consisted of native longleaf
flatwoods and planted slash pine plantations.
There were 19 smaller concentrations of fox squirrels
identified in the state. The habitat base for each of these
populations was estimated at <1,000 ha. Thirteen of these were
on private land, and six on public land. Of the 13 on private
land, nine were on cattle ranches, two on timber land, two on a
quail plantation, and one on a cluster of urban golf courses.
Four of the six small populations on public lands were found
on state parks (Goldhead Branch, Hillsborough River, White Belt,
and Suwannee River), one occurred on a state forest (Cary), and
one occurred on property used for research (University of
Florida, Welatka). The habitat on the areas was primarily
longleaf sandhills and xeric longleaf flatwoods. The
understories were managed primarily using prescribed fire.
In addition to the major concentrations mentioned above and
listed in Table 1, smaller populations were scattered across the
state. The smaller populations were surviving in fragmented
strips and patches of habitat distributed in wooded fencerows,
grazed woodlots, pecan (Carva illinoensis) groves, golf courses,
and on the fringes of low density residential areas. The ground
cover was managed with cattle grazing or mowing. These
scattered, diffuse populations were particularly prevalent on the
small farms in northern Florida. In fact, 10 of the 14 counties
with fox squirrels but without a notable population occurred in
northern Florida (Table 1).
Habitat Features
The vegetative structure of the forests occupied by fox
squirrels in the state was consistent, and easily recognizable.
The habitat was generally park-like in appearance. The forests
had a grassy or otherwise low groundcover, a relatively open
understory, and an overstory of large pines and oaks. The pines
were usually longleaf, or in south Florida, slash pine, but there
were a few sites in northern Florida were the pines were either
loblolly, shortleaf, or sand pine (P. clausa).
Many wildlife professionals contacted during the surveys had
.the impression that fox squirrels were restricted to longleaf
pine sandhills. This turned out to be a too narrow a view,
because fox squirrels were found in a variety of plant
communities in addition to sandhills, including xeric flatwoods,
15
grazed woodlots, hardwood fencerows and golf courses dominated by
introduced plants.
The habitat characteristics observed in this survey are
well documented, both for Florida (Moore 1957, Brady 1977,
Williams and Humphrey 1979, Kantola and Humphrey 1990) and for
other regions of North America (Flyger and Gates 1982, Dueser et
al. 1988, Koprowski 1994). Fox squirrel habitat in the
midwestern United States was described as a wooded savanna (Nixon
et al. 1984), a description that applies to Florida habitat as
well. The plant species differ between regions, but the
structure of the forest remains consistent. Dueser et al.
(1988), for example, found that vegetation structure could be
used to accurately predict if Delmarva fox squirrels woul-d be
found in a particular forest patch.
Habitat Trends
Fox squirrels remain widely distributed in Florida, but the
distribution is patchy, and the species is locally rare in most
of the state because of a lack of habitat. This situation was
not always the case, because Florida once contained vast
quantities of fox squirrel habitat in the form of great, open
pine forests. In fact, open pine forests, dominated by longleaf
pine, were until recently the major forest type in the state
(Kautz 1993).
This began to change in the late 1800's when industrial
logging companies moved their operations from the upper
midwestern states to the southern pine forests. Certainly there
had been logging, turpentining, and land clearing earlier than
this, but the scale was minor in comparison to the changes that
followed the arrival of the logging companies (Williams 1989).
By 1916, some were lamenting the loss of the longleaf forests
(Young and Mustian 1989). By 1936, although greatly depleted,
longleaf forests still covered 3.09 million ha of Florida (Kautz
1993). Over the next 50 years, the coverage of longleaf fell by
88%; in 1987, only 0.38 million ha remained.
The great longleaf forests were replaced by a variety of
other land uses, such as orange groves, shopping centers,
pulpwood plantations, and cattle pastures. There are a few large
longleaf forests protected on public lands, but most of the
remaining forest patches are scattered in and around other land
uses. Fox squirrels still occupy these patches, but they
represent remnant populations, stranded by habitat loss. The
situation is analogous to a lake drying that leaves fish stranded
in pools and puddles scattered over the lake bottom.
The forest changes that have occurred in Florida in the past
100 years, for fox squirrels at least, have made a common species
rare. Fox squirrels are rare mainly because their habitat is
rare, and it is rare because people have made it so.
Similar trends in fox squirrel habitat have occurred in
other southeastern states. Fox squirrels are rare throughout the
region as a result (Weigl et al. 1989). The Delmarva fox
squirrel has been particularly hard hit by habitat loss and it is
currently listed as federally endangered. In contrast to the
situation in the southeast, fox squirrels in the midwest have
benefited from habitat changes associated with human settlement.
Humans have created savannah habitat in the midwest, and fox
17
squirrels have responded with range expansions and population
increases (Flyger and Gates 1982).
The fox squirrels' future in Florida depends on the
availability of their habitat, which will be influenced by a
number of factors. There are several possible scenarios. These
alternative futures are discussed in a later chapter of this
dissertation.
Table 2-1. Distribution of fox squirrels in Florida by county. Habitat quantities estimated for
notable populations: S<1,000 ha; M=1,000-4,000 ha; L>4,000 ha. Abbreviations used: National
Forest (N.F.), State Forest (S.F.), State Park (S.P.), Wildlife Management Area (WMA), National
Wildlife Refuge (NWR), Air Force Base (A.F.B.)
Notable Populations
County (Quantity of Comments
Habitat)
Watermelon Pond
area (S)
Osceola N.F. (M)
None
None
Most remaining habitat scattered on farms in grazed woods.
A few fox squirrels present in uplands on Lochloosa WMA.
Only reports from Osceola N.F.; occur in patches of xeric
flatwoods in Forest and in mowed flatwoods at Olustee
Battlefield.
A few fox squirrels reported to occur in Pine Log S.F. and
around town of Fountain in pecan groves.
A few fox squirrels scattered on farms along New River and
around Santa Fe Lake in grazed woodlots and pecan
orchards.
Alachua
Baker
Bay
Bradford
Table 2-1--continued
County
Brevard
Broward
Calhoun
Charlotte
Notable Populations
(Quantity of
Habitat)
Cattle ranches in
SW corner of county
(M)
None
None
Cecil Webb WMA.
(M), Babcock Ranch
(M)
Comments
Occur on ranches in pine/oak hammocks scattered in
pastures. Locally common. Also a few fox squirrels
scattered in flatwoods on Farmton WMA.
No fox squirrels reported.
A few fox squirrels scattered in northern half of county
in patches of cut-over sandhill. No reports of squirrels
in southern half of county.
Fox squirrels restricted to scattered patches of xeric
flatwoods and pine/oak hammocks on ranches.
Table 2-1--continued
County
Citrus
Clay
Collier
Notable Populations
(Quantity of
Habitat)
Withlacoochee S.F.
(L), Rook Ranch
(M), Hollings Ranch
(M)
Camp Blanding (L),
Gold Head Branch
S.P. (S), Jennings
S.F. (M)
Naples golf courses
(S)
Comments
Fox squirrels common in southeastern part of county. A
few fox squirrels occur in scattered patches of sandhill
elsewhere in county.
Habitat marginal but widespread on Camp Blanding and
Goldhead. Fox squirrels occur elsewhere in sandhill
patches in pastures.
Common on some golf courses. A few squirrels scattered in
xeric flatwoods in Golden Gate Estates, Collier Seminole
S.P., Everglades City, Immokalee Ranch, and Big Cypress
N.P.
Table 2-1--continued
Notable Populations
(Quantity of
Habitat)
Ft. White area on
Cason Farm (S)
None
Small, scattered pockets of fox squirrels; most habitat on
farms in grazed woods and fencerows.
No fox squirrels reported
Carlton Ranch (M)
Mature stand of
slash pine--3 miles
SW of Old Town (S)
DeeDot Ranch (M),
Cecil Field Navy
Base (M)
Bulk of habitat on Carlton Ranch. A few squirrels reported
for Brighthour Ranch.
Fox squirrels only reported for northeastern part of
county; very rare even there. A few squirrels reported
around Guaranto Springs in grazed woods.
Bulk of habitat in county on DeeDot and Cecil Field.
Common in suitable habitat on DeeDot.
County
Columbia
Comments
Dade
DeSoto
Dixie
Duval
Table 2-1--continued
County
Escambia
Flagler
Franklin
Gadsden
Gilchrist
Notable Populations
(Quantity of
Habitat)
La Floresta
Perdido, former WMA
(M)
Ranches bordering
Cresent Lake (M)
St. James Island
(S)
Joe Budd WMA (M)
None
Comments
Fox squirrels restricted to northwestern part of county.
Locally common in longleaf stands managed for pole timber.
Most habitat on Cresent Lake ranches in pine/oak hammocks
in pastures. A few fox squirrels in pulpwood plantations
in remnant patches of xeric flatwoods.
Only report for county from a natural longleaf stand
surrounded by planted sand pine.
Common on Joe Budd. A few fox squirrels elsewhere in
county; restricted to grazed woods and fencerows.
A few squirrels reported around Ginnie Springs, Pleasant
Grove Church, and along S.R. 26 on the east and west side
of Waccasassa Flats. Found in grazed woods and fencerows.
h,
Table 2-1--continued
County
Glades
Gulf
Hamilton
Hardee
Notable Populations
(Quantity of
Habitat)
Lykes Ranch (M)
None
Champion Quail
Plantation (M)
Carlton Ranch (M)
Comments
Only present in county on Lykes property in pine/oak
hammocks in pasture. Rare on the property.
A few squirrels reported on St.Joe seed tree orchard, on
M&K Ranch near Downes Island, on along S.R. 71 south of
White City.
Only reported from western half of county. Other than
quail plantation, a few reported to occur along S.R. 51 on
the Suwannee River.
Bulk of habitat on Carlton Ranch in hammocks and xeric
flatwoods in pastures. A few squirrels reported to occur
south of Wauchula along the Peace River and on the Smoke
Ranch.
Table 2-1--continued
County
Hendry
Hernando
Highlands
Hillsborough
Notable Populations
(Quantity of
Habitat)
Alico, Hilliard,
and Duda Ranches
(M)
Withlacoochee S.F.
(L)
Avon Park A.F.B.
(M), K-D Ranch (M)
Hillsborough River
S.P. (S)
Comments
Most habitat in northwestern corner of county on ranches.
A few squirrels reported for Big Cypress Indian
Reservation.
Fox squirrels common on Withlacoochee S.F. Restricted
elsewhere to remnant patches of sandhill forests found in
subdivisions and golf courses.
Fox squirrels common on K-D Ranch in southeastern corner
of county. A few squirrels reported for Avon Park A.F.B.,
on farms surrounding Highlands Hammock S.P., and along
Fisheating Creek.
A fox squirrels on and around Hillsborough River S.P. and
on ranches in southern part of county.
Table 2-1--continued
Notable Populations
(Quantity of
Habitat)
Comments
Holmes
Indian River
Jackson
Jefferson
LaFayette
None
Ranches west of St.
Johns River marsh
(M)
Apalachee WMA (M)
Quail plantations
(L)
None
Squirrels few and scattered in pecan groves and grazed
woods.
Common in patches of grazed woods on ranches. No
squirrels reported east of St.Johns River.
Common on Apalachee. A few squirrels reported to occur on
Florida Caverns S.P. and in scattered locations along the
Apalachicola and Chipola Rivers.
Common on the numerous quail plantations scattered in
northern half of county. None reported for southern half
of county.
A few squirrels reported to occur in grazed woods on farms
along Suwannee River.
County
Table 2-1--continued
County
Notable Populations
(Quantity of
Habitat)
Ocala N.F. (L),
State lands in
Wekiva River basin
(M)
Alico Ranch (M)
Quail plantations
(L), Apalachicola
N.F. (L)
Williston Highlands
(M)
Comments
Bulk of habitat in Ocala N.F. and on state lands bordering
Wekiva River. A few squirrels reported to occur around
Astatula, Hancock Lake, and Klinger Airport.
Most habitat on Alico Ranch. Also reported on golf
courses and ranchettes built on western edge of Alico.
Fox squirrels common in northern half of county on
plantations. Widely scattered in Apalachicola in patches
of sandhill and xeric flatwoods.
Scattered pockets of squirrels on farms around Chiefland
and in remnant longleaf stands in Williston area.
Lake
Lee
Leon
Levy
Table 2-1--continued
Notable Populations
(Quantity of
Habitat)
Apalachicola N.F.
(L)
None
Taylor (S), Jim
Walters (S), and
Drosey Ranches (S)
County
Ocala N.F. (L)
Bulk of habitat and fox squirrels occur on Ocala N.F. in
longleaf islands. Fox squirrels abundant on Marion Oaks
Golf Course. A few squirrels on horse ranches.
Comments
Bulk of habitat for county in Apalachicola N.F. in
vicinity of Camel Pond. Occur in patches of sandhill and
xeric flatwoods.
Squirrels rare. Bulk of habitat along Suwannee River near
1-10 rest area and along Withlacoochee River near Hickory
Grove Church.
Bulk of habitat on ranches. Occurred in scattered
locations in patches of grazed woods in pastures.
Liberty
Madison
Manatee
Marion
Table 2-1--continued
Notable Populations
(Quantity of
Habitat)
None
County
Martin
Monroe
Nassua
Okaloosa
Okeechobee
White Oak
Plantation (S),
Cary S.F. (S)
Eglin A.F.B. (L),
Blackwater River
S.F. (L)
Williamson Cattle
Co. (M)
Comments
A few squirrels in grazed woods on ranches west of 1-95.
Reported on White Belt and Bluefield Ranchs.
Only reported from Loop Road. Reportedly seen in slash
pines bordering road.
Most habitat along St.Marys River in patches of mature
pines. Populations few and scattered.
This is the largest habitat block in the state.
A few squirrels scattered on ranches in grazed woods.
None
Table 2-1--continued
County
Orange
Osceola
Palm Beach
Notable Populations
(Quantity of
Habitat)
Leo Faurot Ranch
(M), Wekiva Springs
S.P. (S)
Ranches around
Kenansville (L),
Three Lakes WMA (M)
White Belt Ranch
(S) (this property
is state owned)
Comments
Other than Wekiva Springs S.P., most habitat scattered on
ranches in eastern part of county. Common on Leo Faurot
ranch located in southeastern portion of county.
Fox squirrels widespread in county.
Kenansville area.
Common on ranches in
Reportedly only occur in county in grazed woods on White
Belt Ranch.
Ranches (M)
Bulk of habitat and squirrels in central portion of county
on ranches. Also reported to occur in vicinity of Big
Fish Lake.
Pasco
Table 2-1--continued
County
Comments
Notable Populations
(Quantity of
Habitat)
None
Avon Park A.F.B.
(M)
K. Ordway Preserve
(M), Fla. Rock
property (M), Univ.
Fla.--Welaka Unit
(S)
McCormick Ranch (S)
Peacock Ranch (S)
Bulk of habitat scattered in northwestern corner of county
in grazed woods.
Habitat limited to a few pine stands along Bluefield Road
and on Peacock Ranch.
Reported to occur but very rare. Habitat on golf courses
and grazed woods in remaining pastures.
A few squirrels on Avon Park A.F.B. Also occur on ranches
along Kissimmee River.
Habitat scattered across county in remnant stands of
longleaf sandhill. Locally common.
Pinellas
Polk
Putnam
St.Johns
St.Lucie
Table 2-1--continued
Notable Populations
(Quantity of
Habitat)
Comments
Santa Rosa
Sarasota
Seminole
Eglin A.F.B.(L),
Blackwater River
S.F.(L), T.R.
Miller Timber
Co. (M)
None
Ranches around
Geneva(M), Lower
Wekiva River S.P.
(S)
Habitat abundant in eastern half of county. Fox squirrels
common. No habitat or fox squirrels reported for western
half of county.
Fox squirrels few and widely scattered on ranches and in
new subdivisions along 1-75.
Other than the small population on Lower Wekiva, most
habitat on ranches along the St. Johns River. Common on
some ranches.
County
Table 2-1--continued
Notable Populations
(Quantity of
Habitat)
Ranches in NW
corner of county
(M)
Chinquapen quail
plantation(S),
Suwannee River S.P.
None
Circle S Ranch (S)
Comments
A few squirrels on small ranches around Bushnell, but most
habitat and squirrels in northwest corner of county on
large ranches west of 1-75 and north of S.R. 44.
Small pockets of squirrels widely scattered; most found in
pecan groves and grazed woods on small farms.
A few squirrels in remnant patches of sandhill between
Perry and the Gulf.
Squirrels widely scattered in grazed woods; other than
Circle S Ranch, most habitat on farms along New River and
Olustee Creek.
County
Sumter
Suwannee
Taylor
Union
Table 2-1--continued
County
Volusia
Wakulla
Walton
Washington
Notable Populations
(Quantity of
Habitat)
Ranchs and camps
around Lake Dias(M)
St.Marks NWR
(Panacea Unit) (M),
Apalachicola
N.F.(L)
Eglin A.F.B. (L)
Comments
Bulk of habitat around Lake Dias. A few squirrels
scattered in Tomoka WMA in xeric flatwoods.
Bulk of habitat in scattered patches of xeric flatwoods in
Apalachicola and on St. Marks.
Most habitat in county on Eglin A.F.B. Elsewhere found in
pecan groves and grazed woods on small farms.
Habitat on small: farms in pecan groves and grazed woods.
None
CHAPTER 3
POPULATION ECOLOGY
Radio telemetry has become a standard tool for
investigations of wildlife movements and demographics. It has
been used in Florida on two previous studies of fox squirrels.
In the first study, radio transmitters were attached to six fox
squirrels on a sandhill study area in northeastern Florida
(Kantola and Humphrey 1990). In the second study, five fox
squirrels in Collier County were radio-collared and relocated
from golf courses to the Big Cypress National Preserve (Jodice
1993). Both studies have provided valuable insight into fox
squirrel biology in Florida, but both were hampered by small
samples of radio-collared animals. Because of the limited data
that were available on fox squirrel population ecology in
Florida, the current study was initiated.
The study attempted to answer several questions on fox
squirrel population ecology, including: 1. What are the home
range sizes and how are the home ranges spatially distributed? 2.
What are the mortality rates of radio-collared animals, and what
are the important mortality factors? 3. What is the average
litter size, litter frequency, and when is the breeding season?
4. What is the density of fox squirrels on the study areas? 5.
What are the characteristics of subadult dispersal? and 6. How
does the population ecology of fox squirrels in northern Florida
compare to that observed for fox squirrels in other regions in
North America?
STUDY AREAS
The first phase of the study was conducted on Goldhead
Branch State Park and surrounding private property, Clay County.
Field work was conducted there from January 1990 to March 1991.
The 6.9 km2 area was about 80% forested (Figure 3-1); 80% of the
forest cover was longleaf pine/turkey oak) sandhill, 18% hardwood
hammock (primarily oaks), and 2% sand pine scrub. The non-
forested portions of the study area were open water, marsh, or
uplands developed for public use or park maintenance. Hunting
was prohibited on the Park, but the surrounding land was hunted.
Fox squirrels were difficult to trap on Goldhead, and
because of this, the study was moved to a second area in 1991.
The second study area was in southern Columbia County, about 3 km
north of the town of Fort White. Field work was conducted from
January 1991 to June 1994. The primary study area of 2.3 km2
(Figure 3-2) was a patchwork of upland hardwoods (49.3 ha),
pastures and row crops (144.0 ha), and clearcuts (34.3 ha).
There were three residences on the study area (2.8 ha). The
clearcuts were the result of a 1989 logging of planted slash
pines.
The wooded portions of the Fort White area occurred as
fencerows, two closed-canopy hammocks (each about 10 ha in size),
and a wooded but open-canopied pasture (Figure 3-2). Tree
species were predominantly laurel oak (Q. hemisphaerica) and live
oak. Black cherries (Prunus serotina) and dogwoods (Cornus
florida) were common in the fencerows and hammocks. Longleaf
pines were scattered over the area, but they were a minor
component of the forest cover. Cattle grazed most of the study
Goldhead
Study Area
LAND COVER
SANDHILL
HARDWOODS
SANDPINE
OPEN WATER / MARSH
BARREN LAND
1 k m
1 km
Figure 3-1. Goldhead study area, Clay County, Florida.
Ft. White Study Area
Land Cover
RESIDENCE
HARDWOOD
... PASTURE/ROW CROP
iICLEAR CUT
:-PLANTED PINE
1-------------
1km
Figure 3-2. Fort White study area, Columbia County, Florida.
38
area, and their activity kept the hammocks and fencerows clean of
undergrowth. There were four fields planted in peanuts or corn.
State Road 47, a moderately traveled 2-lane highway, formed the
western border of the primary study area. The landowners on the
study area allowed gray squirrel (S. carolinensis) hunting, but
they protected fox squirrels. This had been their practice
before the study began and continued during the study.
METHODS
Capture Procedures
Adult and subadult fox squirrels were captured in live
traps. Two were caught in wooden traps (61 cm long) modeled
after the design of Ludwig and Davis (1975). All other trapped
fox squirrels were caught in wire traps (Tomahawk brand, Models
103, 104, and 105). Raw, dried peanuts in the hull were settled
on as the bait of choice, but only after using a variety of
baits, including dried corn (shelled and on the cob); fresh,
grocery store mushrooms; peanut butter and raisin mix, suspended
in the trap in a cheese cloth sack; and scented lures, including
anise and artificially flavored extracts of strawberry, banana,
and walnut.
Traps were checked in the morning and again in the evening.
Traps were left open overnight prior to 1993, but after that they
were tripped in the evening and reset the following morning.
This eliminated the capture of nontarget, nocturnal species such
as raccoons (Procyon lotor), opossums (Didelphis virginiana), and
striped skunks (Mephitis mephitis). It also eliminated the
possibility of a fox squirrel spending the night in a trap.
Prior to handling, trapped fox squirrels were calmed by
covering the trap with a jacket or towel. Next, a mesh nylon
sack with a drawstring was placed over the door end of the trap.
The drawstring was tightened and the door was opened with the bag
in place. The jacket was then removed, and the squirrel was
flushed into the bag for handling.
Animals requiring extensive handling were tranquilized with
an injection in the hip of 100mg/cc ketamine hydrochloride. As a
rule of thumb, all adult-sized squirrels (weight >950grams) were
drugged with a dosage of 0.3 cc/squirrel. This dosage was
reduced to 0.25cc/ adult squirrel in the later portions of the
study. Lighter squirrels were normally given less drug, but it
was found that 0.2 cc was a minimum dose for handling squirrels
>800 g. The reaction of the squirrels to the tranquilizer was
variable: some squirrels succumbed and were limp within 2 minutes
of injection, but others never went fully under -- they continued
to move and crawl but made no attempt to bite and were safely
handled. Animals tranquilized in the afternoon were routinely
held overnight in traps placed in a storage shed to allow them to
fully recover from the drugs before their release. They were
released at the capture site the next morning.
Recaptured animals that were only physically examined were
processed in the mesh bag without using tranquilizers. These
squirrels made no attempt to bite, but some kicked without
warning with razor-clawed hind feet.
Fox squirrels were weighed to the nearest 25g with a spring
scale. Body weights of adult animals were compared by sex using
a nested ANOVA.
Subadults and adults were tagged in each ear with a monel
tag (National Band and Tag Co., Size #1). Squirrels >700grams
were radio collared. The transmitters used were either Telonics
M080 or Holohil MI-2M. Fox squirrels on Goldhead were also
marked by toe clipping one digit, but toe clipping was not used
at Fort White. Nestlings from 2 litters handled on Fort White
were marked on their leg pelage with a leather dye, and nestlings
from a third litter were tagged in one ear with an adult eartag.
Estimates of Age and Sexual Maturity
Age estimates were assigned to fox squirrels based on
criteria presented by Moore (1957) and Flyger and Gates (1982).
Nestling fox squirrels with hair on their backs were considered
at least 10 days old, and nestlings with open eyes were
considered at least 4-5 weeks (Flyger and Gates 1982). The age
of males caught in traps was assessed by body size, testes
descent, and the amount of hair on the scrotum. Males with
undescended testes and heavily furred scrotums were considered <8
months old. Males <900g with testes .3.5cm and mostly furred
scrotums were aged as 8 months old; the testes on these squirrels
were assumed to have just descended. Males >900g with scrotal
testes and sparsely furred, black scrotums were considered
monthss old. Female fox squirrels <900g were considered <5
months old.
The age in months for squirrels <9 months old was estimated
by backdating from the date of capture to the appropriate winter
or summer birthing periods. Animals thought born in the summer
birthing period were assigned an August 1 birthday; winter born
animals were assigned a January 1 birthdate.
Sexual maturity of males was assessed by testes size and
scrotal characteristics. Males with undescended testes and
furred scrotums were considered sexually immature. Males with
large, swollen testes (>3.5 cm long) and black, mainly furless
scrotums were considered sexually mature. Sexual maturity of
females was assessed by nipple characteristics (McCloskey 1977).
Females with nipples <1 mm long that looked like they had never
been suckled were considered sexually immature. Females with
nipples >3mm were considered sexually mature and thought to have
bred.
Telemetry
Radio-collared fox squirrels on Goldhead were located as
time permitted using triangulation procedures from fixed
stations. Data were recorded by station number and azimuth. Fox
squirrels on the Fort White area were normally located 2-3
times/week. All locations there were plotted in the field on
aerial photographs (scale, lcm=48m), and the data were recorded
as Universal Transmercator Grid (UTM) coordinates. Squirrels
were located using standard triangulation procedures or by
walking or driving to the tree where the squirrel was located. A
fixed-wing airplane was used to search for squirrels that could
not be found from the ground. The Fort White study area was
open, and visibility for seeing fox squirrels on the ground was
.normally unimpeded. Locations on the Fort White study area were
extremely accurate because of the visibility and the attempts to
pinpoint most locations to the nearest tree or clump of trees.
Attempts were made on both study areas in the initial months of
field work to locate animals more than once daily to obtain daily
42
activity data. This was discontinued on Goldhead because of time
constraints and on Fort White because of the influence that
observers had on squirrel movements.
Home range sizes were estimated by the harmonic mean and
convex polygon methods using the computer program TELEM. Pre-
dispersal (natal) and post-dispersal (adult) home ranges were
calculated for fox squirrels that dispersed from the study area.
Transition locations between home ranges were discarded from the
analysis. Home range sizes of adult males and adult females were
compared using the Mann-Witney test (p<0.01).
Habitat Use Versus Availability
Habitat use was determined by assigning each location to one
of the major cover types. The four habitat types used for the
analysis on the Goldhead study area were sandhill, hardwood,
scrub, and barren land (or non-forested land). The habitat types
used on the Fort White area were hardwood, planted pine, wooded
pasture, and field (includes pastures, rowcrops, and clearcuts).
Habitat selection of non-dispersing squirrels was examined with
Friedman's method (Alldredge and Ratti 1986). The difference
between proportion used and proportion available for each habitat
type was computed for each animal. These differences were ranked
for each animal (lowest to highest), and the ranks were used to
compute Friedman's test statistic (habitat types were considered
as "treatments" and animals as "blocks"). If Friedman's test was
significant, then a signed rank test was used to determine
differences among use versus availability for each of the habitat
types.
Mortality Rates
Annual mortality rates were calculated with the computer
program MICROMORT (Heisey and Fuller 1985). The daily survival
rate was assumed constant for the study period. A z-statistic
was used to compare mortality rates for males and females and for
residents and dispersers. In addition to the confirmed deaths
of radio-collared squirrels, radio contact was lost with other
squirrels for unknown reasons. It was assumed these squirrels
died. Two mortality rates were calculated: one used only the
confirmed deaths; the second used the number of confirmed deaths
plus the number of assumed deaths.
Reproduction
Female fox squirrels have the potential for producing two
litters/year, one in winter and one in summer (Flyger and Gates
1982). The frequency of litters from radio-collared females for
each potential reproductive period in 1991, 1992, and 1993 was
assessed using movement data, capture data, sightings of
subadults, sightings of females that appeared to be nursing, and
nest checks in 1992 and 1993.
Food Habits
Anecdotal data on food habits also were collected on the
Fort White study area. Whenever fox squirrels were seen eating,
attempts were made to identify the foods. The food habits data
are presented by season using the following seasons: winter
(January February), spring (March-May), summer (June-August),
and fall (September-December).
RESULTS AND DISCUSSION
Capture Success
Six adult fox squirrels (3 male:3 female) and one nestling
(male) were captured on Goldhead. Five of the six adults were
caught in traps (2,877 trap days, or 1 capture/575 trap days);
one adult female and her nestling were caught in a nest box built
by Park personnel for kestrels (Falco sparverius). Five of the
six adults on Goldhead were radio collared. The adult not
collared was caught at the end of the study during attempts to
catch the radio-collared squirrels for collar removal.
Forty-four fox squirrels (27 male:17 female) were captured a
total of 120 times in 3,486 trap-days on the Fort White study
area (1 capture/29.1 trap days). Thirty-nine of the squirrels
were radio-collared. One fox squirrel died after handling. Four
squirrels caught in traps were not collared, either because they
were too small (n=2) or because they were captured at the end of
the study (n=2) during attempts to catch radio-collared squirrels
for collar removal. Thirteen fox squirrel nestlings were also
handled; 11 of these were sexed (4 male:7 female) and eight were
marked with either dye or eartags.
Body Weights
Weights were taken on five adult fox squirrels (2 male:3
female) on Goldhead. The average weight of males was 1,055 grams
(SE 55); the average weight of females was 1,075 grams (SE 80).
The weights were not compared statistically because of the small-
samples.
Weights were taken on 30 adult fox squirrels (22 males:8
females) on Fort White. The average weight of males was 999
45
grams (SE 10); the average weight of females was 1,120 grams (SE
14). Females were significantly heavier than males (p=0.0003).
Wood (1988) and Larson (1990) also reported that adult females
were heavier on average than adult males, although Wood (1988)
stated the differences in his data were not significant. Other
studies have found no significant differences in the weights of
males and females (Flyger and Gates 1982, Weigl et al. 1989).
Home Range Sizes
The minimum convex polygon home ranges on Goldhead ranged
from 19.4 to 95.8 ha (Table 3-1). The average home range size
for the two males (83.0 ha; SE 9.1) was over twice the mean size
for the three females (35.6; SE 9.6).
The average convex polygon home range size on Fort White for
17 adult males (79.5 ha; SE 8.3) was significantly larger
(p<0.01) than the average home range size for 12 females (33.0
ha; SE 4.9) (Tables 3-2 to 3-4). The natal home ranges of eight
subadults averaged 6.35 ha (SE 1.76). Five animals monitored on
the Fort White area did not clearly fit into the category of
adult or subadult. The home ranges for these animals appears in
Table 3-5.
Home ranges for both study areas also were calculated using
the harmonic mean method. Based on the time I spent in the field
tracking the squirrels, my opinion is that the 80% harmonic mean
estimate represented the area where the squirrels were usually
found. The average home range sizes using 80% of the locations
were as follows: Goldhead -- adult males (n=2) 29.5 ha; adult
females (n=3) 22.1 ha; Fort White -- adult males (n=17) 35.7 ha
(SE 4.7); adult females (n=12) 12.8 ha (SE 2.4); subadults (n=7)
Table 3-1. Home range sizes (ha) of adult fox squirrels on the
Goldhead study area by the harmonic mean (HM) and minimum convex
polygon (MCP) methods.
HM HM HM
Sex/# Monitoring Period # 65% 80% 95% MCP
Locations ha ha ha ha
M390 01/25/90 02/12/91 134 24.1 33.0 74.7 70.3
M340 02/01/90 03/05/91 100 11.3 26.0 96.9 95.8
F300 02/09/90 08/03/90 67 6.0 9.4 25.4 19.4
F430 02/06/90 05/20/90 59 13.1 23.4 33.8 28.9
F410 02/02/90 03/05/91 104 20.5 33.7 56.6 58.4
Table 3-2. Home range sizes (ha) of subadult fox squirrels on the
Fort White study area by the harmonic mean (HM)
convex polygon (MCP) methods.
and minimum
HM HM HM
Sex/# Monitoring Period
65%
Locations
1.9
F069 11/05/92 -
03/22/93
F630 11/04/92 -
02/24/93
F870 11/07/92 -
03/20/93
M129 10/03/91 -
05/11/92
M130 02/04/91 -
04/17/91
M150 02/05/91 -
2.7
0.6
1.3
3.1
6.0
ha ha
2.6
3.5
1.1
2.5
7.0
10.7
5.6
7.8
5.'8
33.5
11.9 22.9
03/06/91
M170 02/01/91
06/10/91
80%
95%
MCP
3.0
14.3
13.6
2.3
4.6
5.4
6.1
Table 3-3. Home range sizes
on the Fort White study area
minimum convex polygon (MCP)
48
(ha) of adult female fox squirrels
by the harmonic mean (HM)
method.
and
HM
65%
Sex/# Monitoring Period
F010 01/15/91
F069a 04/07/93
F070b 04/21/93
F099b 03/17/92
F100 03/18/91
F120 02/04/91
F140a 06/16/91
F260 01/18/91
F270 01/21/91
F429 02/03/93
F630a 03/11/93
06/01/93
F870a 04/30/93
10/17/93
- 12/07/92
- 08/11/93
- 01/28/94
- 04/29/94
- 01/28/94
- 06/25/92
- 09/22/92
- 06/23/94
- 04/29/94
- 04/16/94
- 04/29/93
- 11/07/93
- 10/03/93
Locations
227
40
73
169
318
185
146
325
318
121
22
65
46
- 11/19/93 13
HM
80%
ha ha
8.7
9.2
1.8
2.7
1.4
13.6
12.2
6.9
1.4
11.1
4.6
3.7
12.4
14.2
14.3
2.5
5.3
3.3
26.6
21.0
16.4
2.8
22.8
10.0
6.5
23.0
4.2 8.7
HM
95%
ha
42.2
70.0
4.8
10.9
25.5
53.4
42.5
41.2
7.5
42.3
15.8
30.0
33.0
MCP
ha
47.9
55.4
3.4
9.1
30.7
44.9
42.7
42.4
17.2
47.0
10.4
28.6
26.3
14.9 8.9
a Post dispersal home ranges. F069 remained on the primary study
area after dispersal, but the other three females (F140, F630,
and F870) left the area.
b F070 and F099 attained sexual maturity during the monitoring
period.
Table 3-4. Home range sizes (ha) of adult male
the Fort White study area by the harmonic mean
convex polygon (MCP) method.
HM
65%
Sex/# Monitoring Period
Locations
fox squirrels on
(HM) and minimum
HM HM
80%
95%
MCP
ha ha ha
M049 11/05/92
108
24.4 38.8 165.5 96.3
04/27/94
M090 02/05/91
189
39.4 72.4 183.3 134.4
08/31/92
M119 01/29/93
113
13.8 28.7 78.2 75.7
03/21/94
M128a 02/03/93
03/09/94
M130a 05/01/91
7.2
149
13.7 166.7 76.7
10.0 21.6 37.5 44.5
06/23/92
M150a 03/19/91
14.3 34.8 76.8 60.5
09/23/91
M159 03/17/92
225
3.7
8.3
53.7 38.7
04/27/94
M210 06/06/91
9.9
62.3 132.8 125.4
04/04/94
M239 01/29/93 -
16.2 39.0 100.2 71.5
07/19/93
M240 12/31/91
252
7.9
29.0 78.3 115.7
04/08/94
Table 3-4--continued
Sex/# Monitoring Period
M259 04/20/93 -
12/12/93
M300 11/07/91 -
04/06/92
M308 09/07/93 -
06/24/94
M368 12/31/91 -
04/27/94
M430 01/03/92 -
09/06/92
M540 01/06/93 -
07/01/93
M690 03/18/92 -
12/09/93
a Post-dispersal home ranges.
Locations
Locations
HM
65%
ha
HM
80%
ha
HM
95%
ha
MCP
ha
20.1 43.3 91.4 75.3
30.8 51.8 167.7 101.3
5.1
263
5.4
12.4 30.1 22.8
14.8 30.5 37.1
17.4 31.0 86.0 67.6
16.0 38.5 126.7 75.3
135
37.3 67.2 178.8 132.3
Table 3-5. Harmonic mean (HM) and minimum convex polygon (MCP)
home range sizes (ha) of fox squirrels captured as subadults
whose sexual maturity during the period of monitoring was
unknown, but suspected to be that of a subadult (the possible
exception is M188, who may have been sexually mature during the
period shown below).
HM HM
65% 80%
Sex/# Monitoring Period
95%
Locations
ha ha ha
F370 11/07/91 08/19/92a
F869 03/03/93 12/07/93
M128 02/03/93 10/12/93b
M160 02/04/91 09/18/91
M188 12/16/93 04/01/94
7.0 8.6
6.5 9.7
MCP
ha
12.6 11.2
13.7 12.6
23.7 37.2 46.0 39.9
2.0 3.8
3.5
10.1
8.9
8.1
10.0
a F370 slipped her radio collar one month after capture and was
last located with telemetry methods on 12/07/91. She was sighted
3 times subsequently, with the last confirmed sighting on
08/19/92.
b Unlike the other fox squirrels in the table, M128 dispersed
from the primary study area; his post-dispersal home range
appears in Table 4.
Table 3-6. Comparison of fox squirrel home ranges in the
southeastern Coastal Plain (minimum convex polygon method). Data
from this study are for adult squirrels only. The other studies
did not report the ages or sexual maturity of the squirrels they
monitored.
Home Range Size (ha)
Reference
This study
Location
Florida
Goldhead
Florida
Fort White
Males
83.0 (n=2)
79.5 (n=17)
Females
35.6 (n=3)
33.0 (n=12)
Kantola (1986)
Florida
40.0 (n=4)
20.6 (n=2)
Putnam County
Powers (1993)
Alabama
Conecuh
38.0 (n=14)
11.6 (n=9)
Edwards (1986)
National Forest
South Carolina
31.6 (n=9)
19.3 (n=4)
Georgetown
Weigl et al.
(1989)
North Carolina
Coastal Plain
26.6 (n=8)
17.2 (n=14)
4.7 ha (SE 1.4). Two other harmonic mean estimates of home range
size were calculated (65% and 95%). These estimates are
presented in the home range tables as a reference for those who
may find the information of value.
The home range sizes determined in this study were compared
to those determined in other studies conducted in the
southeastern United States (Table 3-6). Home ranges of males in
all studies were larger than those of females.
The home ranges of both sexes on Goldhead and Fort White
were almost double the size of those found in other studies.
There are several possible explanations for these differences.
One may be due to differences in food abundance between areas.
As an example, fox squirrels on Goldhead may have had large home
ranges because of low food abundance in comparison to the other
study areas in the southeast. Fox squirrels on Goldhead also
occurred at relatively low densities (Table 3-12), and low food
abundance would explain both the low densities and large home
ranges. The large home ranges on the Fort White study area were
believed a result of habitat distribution. The forested habitat
was distributed in fencerows and hammocks scattered in fields and
pastures. The pattern may account for the large home range sizes
there relative to other areas where the habitat was more
continuous. Other differences in home range sizes between study
areas may be due to differences in sample sizes of radio-collared
animals and the duration of telemetry monitoring.
Spatial Relationship of Home Ranges
The spatial relationships of the home ranges of adult fox
squirrels are illustrated in Figures 3-3 to 3-11. I tried a
number of ways to depict the characteristics I observed in the
field, and the method used here was the best I found. The
figures contain the complete set of locations for each of the
home ranges that are illustrated. The vertical spikes on the
graphs represent sites with frequent locations. These normally
represent locations of preferred nests. The graphics may at
first glance look too "busy" to interpret, but in my opinion,
they are worth taking the time to "read".
The home ranges for the three adult females tracked on
Goldhead displayed minimal overlap (Figure 3-3). This pattern
also observed for adult females on the Fort White study area
(Figures 3-4 to 3-7).
Two males were radio-tracked on Goldhead, and although there
was no overlap between them, there were too few data to evaluate
the spatial arrangement of adult males on the Goldhead area
(Figure 3-8). Although adult males were generally solitary,
their home ranges on Fort White overlapped extensively with those
of adult females and other adult males (Figures 3-9 to 3-11).
The natal home ranges of subadults monitored on the Fort White
area were within their mother's home ranges.
There was one exception observed regarding the separate home
ranges of adult females. In this case, a subadult that did not
disperse attained sexual maturity while within the range of the
female believed to be her mother. The spatial arrangement of
home ranges and the behavior behind the patterns is discussed in
the end of this chapter.
FREQUENCY
0 F300 0 F410 0 F430
0--
O -
1 km
Figure 3-3. Spatial relationship of three adult female fox squirrels radio-tracked on the
Goldhead study area.
K/ -
FREQUENCY
c F1Q00 O' F260
500m
Figure 3-4. Spatial relationship of two adult female fox squirrels radio-tracked on the
Fort White study area.
FREQUENCY
60
SF099 [] F270
45
30
15
500m
Figure 3-5. Spatial relationship of two adult female fox squirrels radio-tracked on the
Fort White study area.
\\ _- ^^\ ^ A ^^_-
\ ---\- \ \ ,_-----^'^
\ _----- \ ^ -- ^----- ________________________________
\.^- ~^^^'^500
Fiur 35.Sptil eatonhi o to dutfeal fx qurrl rai-trake onth
Fort White- stuy rea y
rTnC-IuINI' I
0 FO10 0 F120
500m
Figure 3-6. Spatial relationship of two adult female fox squirrels radio-tracked on the
Fort White study area.
V F010
A F099
0 F100 0 F120
-' F260
E F270
0 F429
500m
Figure 3-7. Spatial relationship of seven adult female fox squirrels radio-tracked on the Fort
White study area.
FREQUENCY
V F300 O M340 0
M390
0 F410 0 F430
N
s~- -\ --
- S
1 km
Figure 3-8. Spatial relationship of three adult female fox squirrels and two adult male fox
squirrels radio-tracked on the Goldhead study area.
FREQUENCY
60
45
---
\
^. -
\
\.
FREQUENCY
A M090 v
F010
0 F120
K
500m
Figure 3-9. Spatial relationship of two adult female fox squirrels and one adult male fox
squirrel radio-tracked on the Fort White study area.
FREQUENCY
60
45
30
15
0
0 F100 0 M210 O F270 O M368
j0---4- <,"----
S - -
S -- S
S
500m
Figure 3-10. Spatial relationship of two adult female fox squirrels and two adult male fox
squirrels radio-tracked on the Fort White study area.
FREQUENCY
60
2 M049 O M259 > M430
45
15
0- -'
-
[- > [> __[- 0
-" 500m
-El
Figure 3-11. Spatial relationship of three adult male fox squirrels radio-tracked on the Fort
White study area.
Habitat Use Versus Availability
Fox squirrels on the Goldhead area were located most
frequently in sandhill (Figure 3-12). The second most commonly
used habitat was hardwoods. There was no significant difference
in habitat use versus availability (p=0.145).
On Fort White, fox squirrels were located most often in the
hardwood fencerows and hammocks (Figure 3-13). Friedman's test
indicated that habitat use on the study area was not in
proportion with availability (p=0.001). When the four habitat
types on the study area were examined individually using the
signed rank test, it was found that wooded pasture was used in
proportion to its availability (p=0.795), however, the other
three habitat types were not used in proportion to their*
availability (p=0.0001 for each of the three types). Hardwood
fencerows and hammocks were used in greater proportion than their
availability, while planted pines and fields were used in smaller
proportion than their availability.
Dispersal
Ten fox squirrels dispersed during the study (Table 3-7).
Seven dispersed between the estimated ages of 7-9 months old, and
one dispersed at an estimated age of 14 months. The other two
dispersers were also believed to be subadults at the time of
dispersal, but their exact ages were unknown. Two of the ten
squirrels that dispersed left their natal home ranges in October,
and the other eight dispersed between late February and mid-June
(Table 3-7).
The distances between natal and adult home ranges varied
from 1.0km to 7.2km. The average dispersal distance was 3.7 km
0.8
0.7
0.6
0.5
c
o 0.4-
0.4
0
E
0.3
0.2
0.1
0.0
c P c P c P c
CD CD 0 CD
Barren land Hardwoods Sandhill Sandpine
Figure 3-12. Habitat available versus habitat used by fox
squirrels radio-tracked on the Goldhead study area.
C 2 c S C
(D a
Wooded pasture
Figure 3-13.
Habitat available versus habitat used by fox
squirrels radio-tracked on the Fort White study
area.
Field
Hardwood
Planted pine
for males and 3.3 km for females. Two females moved from their
first adult home range to a second adult home range. The
distances between the two adult home ranges were 5.4km for F630
and 2.0km for F870. The second adult home ranges were 3.1 km
(F630) and 3.6 km (F870) from the natal home ranges.
Two of the ten squirrels that dispersed were killed or their
radio signals were lost during dispersal. Seven of the eight
that seemed to have completed their dispersal movements during
the monitoring period settled in areas that contained other fox
squirrels, based on subsequent sightings of fox squirrels in
their adult home ranges. No other fox squirrels were sighted in
the adult home range of one of the eight squirrels, but the post-
dispersal monitoring period for this squirrel was brief because
he was killed by a bobcat (Lynx rufus) about one month after
dispersal.
Fox squirrels dispersing from the Fort White study area had
a limited choice of habitats within the distances they dispersed.
Basically, they could choose agrarian land, either in row crops
or pastures, with scattered hardwood hammocks and fencerows, or
they could choose planted slash pine plantations. Seven of the
eight chose habitat that was primarily agrarian and, thus,
similar in composition and structure to the habitat in their
natal home ranges. The one exception occurred with a female fox
squirrel that dispersed to a 15-20 year old slash pine
plantation.
Several of the radio-collared subadult fox squirrels did not
disperse. Five females captured as subadults were monitored for
Table 3-7. Summary
1994.
Sex/# Date of
First
Capture
F140 04/23/91
F630 11/04/92
F870 11/07/92
F069 11/05/92
M130 02/04/91
M170 02/01/91
M150 02/05/91
M129 01/03/92
M630 10/01/92
of subadult fox squirrel dispersal, Fort White study area: January 1991-June
Estimated Age at First
Capture (Months)
Unknown
3 months
3 months
3 months
6 months
>9 months
8 months
5 months
8 months
Last Known
Date in Natal
Home Range
05/07/91
02/24/93
03/20/93
03/22/93
04/17/91
06/10/91
03/06/91
05/11/92
10/16/92
First Known
Date in
Adult Home
Range
06/16/91
03/11/93b
04/30/93c
04/07/93
05/01/91
06/15/91d
03/19/91
05/19/92
10/19/92e
Estimated
Age at
Dispersal
Unknown
7 months
7 months
7 months
9 months
>13
months
>10
months
9 months
8 months
Dispersal
Distance
(km)
5.5
2.0
5.6
1.0
1.1
7.2
6.5
4.0
1.3
Table 3-7--continued.
Sex/# Date of Estimated Age at First Last Known First Known Estimated Dispersal
First Capture (Months) Date in Natal Date in Age at Distance
Capture Home Range Adult Home Dispersal (km)
Range
M128 02/03/93 6 months 10/12/93 10/29/93 14 months 2.4
a F140's small nipples suggested she was a sexually immature, and therefore a subadult when
captured.
Her exact age at the time of capture was not known.
b F630 remained in this area from 03/11/93 to 04/29/93. She then traveled 5.4km to her second
post-dispersal home range. She remained there from 06/01/93 to 01/17/94, at which time the
battery in her transmitter failed. The second post-dispersal home range was 3.1 km from her natal
home range.
c F870 remained in this area from 04/30/93 to 10/03/93. She then moved 2km to her second post-
dispersal home range. She occupied this second area from 10/17/93 to at least 11/19/93. She was
killed by a vehicle sometime in the week after her last location. The second post-dispersal home
range was 3.6 km from her natal home range.
d M170 was last located 06/18/91, after which the signal was lost. An aerial search was conducted
06/27/91, without success, and it was concluded the transmitter had failed.
e M630's carcass was found 10/20/92, the day after he was located in the new area. It is unknown
how far he would have gone had he survived.
>300 days; three of the five dispersed. Nine males captured as
subadults were monitored for >133 days; five of the nine
dispersed.
Young fox squirrels of both sexes dispersed. Koprowski
(1996) also observed that both sexes of fox squirrels dispersed.
These observations are unusual in that the normal pattern in
mammals is for males only to disperse (Greenwood 1980). The fact
that female fox squirrels dispersed may be related to the
intolerance that adult females have towards other females.
Recruitment
There were two sources of recruitment into the adult segment
of the Fort White population. The first were animals born on the
study area. As previously noted, six of the 14 radio-collared
subadults did not disperse. Recruitment was documented for three
of the six. One of these was a female, and the other two were
males. Both males participated in breeding activities as they
grew older. Sexual maturation of the female was assessed by
nipple characteristics observed through binoculars. As she
matured, her nipples enlarged and darkened. This was taken as
evidence that she reached sexual maturity on the study area.
The other three non-dispersing squirrels either died or were lost
from radio contact before they reached sexual maturity.
The second source of recruits were animals that immigrated
to the study area. I did not have proof of immigration, but, in
two instances, I suspected that "new squirrels" were recent
immigrants to the study area. In both instances the squirrels
were males which suddenly appeared. Both squirrels had descended
testes when they arrived on the study area, and both were
captured soon after being first sighted. They remained in the
capture area during the period they were monitored (six months
for one squirrel and nine months for the other).
Mortality
One of the five squirrels monitored on Goldhead died during
the study. The squirrel, an adult female, was believed killed
by a raptor based on the condition of the carcass. When the body
was found, the skin of the legs was turned inside out. The sign
was indicative of raptor feeding (B. Millsap, GFC, personal
communication).
Nineteen fox squirrel deaths were documented on Fort White
(16 squirrels were radio-collared and three were unmarked). Nine
deaths were due to predation, one death was due to unknown
causes, and nine deaths were due to human-related factors (six to
vehicles, one to a steel trap set by the landowner for coyotes,
one to drowning in a metal drum, and one to capture stress). A
total of 16 of the 39 animals radio-collared died during the
study (Table 3-8).
Two instances of nest predation were observed at Fort White.
During the winter of 1991-92, the leaf nests of two radio-
collared females were found destroyed. Both females were thought
to have had young when the nests were destroyed. Large buteo
hawks have been observed attacking squirrels that were hiding in
leaf nests (B. Millsap, M. Cantrell, GFC, personal
communication). Based on these observations, and the fact that
red-tailed hawks (Buteo jamaicensis) were the only large hawk
seen on the study area, I suspect that the nests were destroyed
by a red-tailed hawk that was digging after the nestling
72
squirrels. Nest loss of this type was seen only twice, and, if a
red-tail was responsible, it may have been a transient bird that
had learned the technique of hunting squirrels in their nests.
Although red-tailed hawks were year-round residents on the
Fort White area and suspected of destroying these two nests,
their impact on radio-collared squirrels was less than I
expected. I had been anticipated that they would be a
significant predator of the fox squirrel. They are known to prey
on fox squirrels in Florida (B. Millsap) and they were commonly
seen hunting on the area. In addition, the habitat was open,
providing good hunting conditions for the hawk, both species were
active at similar times, and furthermore, the squirrels were
often seen foraging or traveling across open pastures where they
seemed extremely vulnerable. However, only three fox squirrel
deaths could be attributed to raptors (all believed due to red-
tailed hawks, the only large raptors seen on the study area).
The minimal impact of red-tailed hawks to fox squirrels on
the Fort White area may be due to two factors. One may be that
they normally select smaller prey than fox squirrels, and the
second may be that fox squirrels have excellent defenses against
hawk attacks. Regarding the latter, fox squirrels crossing open
pastures ran with a loping, stop-and-go pattern of travel. They
sat up on their haunches when they stopped and scanned the area
for a fewseconds before loping off again. Fox squirrels foraging
on the ground behaved similarly in that they stopped frequently,
sat on their haunches, and looked around. The squirrels often
flicked their tails above their backs when running and foraging,
a behavior which might attract the attack to the tail rather than
to the body. These behaviors, in addition to the squirrel's
large body size, may have reduced their vulnerability to red-
tailed hawk predation.
Other predators that were seen on the study area included
bobcats, coyotes, domestic dogs (Canis familiaris), gray foxes
(Urocyon cinereoargenteus), and diamondback rattlesnakes
(Crotalus adamanteus). Owls were not seen or heard on the study
area.
Bobcats were thought responsible for three deaths of radio-
collared squirrels and canids for three deaths (Table 3-8). Two
of the squirrels that canids killed were found buried. When the
carcasses were found, they were intact, and it looked like the
uneaten bodies had been cached. The size of the bite marks on
the dead squirrels suggested the predator was either a small
domestic dog or coyote.
Mammalian predators seemed to be rare on the primary study
area based on sightings and tracks, yet they killed twice as many
radio-collared animals as the more common red-tail hawks. This
suggests that fox squirrels may be more vulnerable to predation
by bobcats and canids than to predation by red-tailed hawks.
Several factors may have reduced the fox squirrel's vulnerability
to mammalian predators and thus kept the mortality within
sustainable limits. One was that contact was reduced by activity
periods with minimal overlap, in that the fox squirrels were
diurnal whereas the mammalian predators were generally nocturnal.
A second factor was that fox squirrels seemed to minimize the
time spent foraging or traveling in open areas more than 20m from
trees where they were vulnerable to being chased and caught;
normally they tended to stay close to the safety of the trees. A
third factor that may minimize mammalian predation is that fox
squirrels seemed to prefer habitats with low ground cover. There
may be two advantages to the low groundcover: first, it was
easier to traverse to escape a pursuer and second, in low ground
cover, the squirrel's vision was unimpeded by vegetation, making
escape from approaching predators more probable. An
unsustainable vulnerability to mammalian predation may be a
primary reason why fox squirrels do not inhabit forests with a
dense understory.
Mortality Rates
Annual mortality rates were calculated for the
radio-collared fox squirrels on Fort White (Table 3-9). There
were 10 confirmed male deaths and five confirmed female deaths
(the one death due to capture stress was excluded from the
calculations). In addition to the confirmed deaths, radio
contact was lost on three other males. The possibility that they
died is reflected in the bracketed values presented in Table 3-9.
The annual mortality rate for all radio-collared squirrels
was about 30% (Table 3-9). Similar mortality rates were observed
by Nixon et al. (1986) for an unexploited fox squirrel population
in Illinois.
Mortality rates of resident and dispersing squirrels were
compared by sex, with the expectation that dispersing squirrels
would suffer higher mortality rates than resident animals.
Although the average mortality rates were higher for squirrels
that dispersed (Table 3-9), the differences were not significant
(p>0.05). A comparison also was made between the mortality rates
Table 3-8. Summary of fox squirrel mortality, Fort White study
area: January 1991
-June 1994.
Sex/#
F120
F069
F870
F869
F100
M300
M090
M289
M260
M160
M150
M129
M630
M890
M239
M259
Last Date
Known
Alive
06/23/92
08/09/93
11/19/93
12/09/93
01/28/94
04/06/92
08/31/92
05/10/93
02/11/91
09/16/91
09/20/91
06/19/92
10/19/92
01/05/93
07/16/93
12/17/93
Cause of Death
Date
Carcass
Found
06/25/92
08/11/93
Nov.,93
12/13/93
01/31/94
04/08/92
Sept.,92
05/11/93
02/12/91
09/18/91
09/25/91
06/23/92
10/20/92
01/06/93
07/19/93
12/21/93
Predation, red-tailed hawk
Predation, bobcat
Roadkill
Predation, canid
Predation, canid
Predation, raptor
Roadkill
Roadkill
Drowned in a barrel
Predation, suspect canid
Predation, raptor
Predation, bobcat
Predation, suspect bobcat
Capture stress
Unknown
Roadkill
Table 3-9. Annual mortality rate of fox squirrels radio monitored on the Fort White study area,
1991-94. Rates calculated by the methods of Heisey and Fuller (1985). Contact was lost with
three radio collared males, one for unknown reasons, and the other two because they lost their
collars, perhaps after death. These three males represent the assumed deaths in the table below.
Confirmed Deaths
(Assumed Deaths)
Mortality Rate -
Confirmed Deaths
(Confirmed + Assumed
95% CI -Confirmed Deaths
(Confirmed + Assumed Deaths)
Deaths)
Males
Residents
Dispersers
All Males
Females
Residents
Dispersers
All Females
All Squirrels
7,321
1,462
8,783
6,780
1,615
8,395
7 (2)
3 (1)
10 (3)
0.29 (0.36)
0.53 (0.63)
0.34 (0.42)
0.09 -
0.00 -
0.15 -
0.15
0.36
0.20
0.00 -
0.00 -
0.03 -
0.45 (0.14 0.52)
0.80 (0.02 0.86)
0.49 (0.21 0.57)
0.29
0.66
0.34
0.15 0.38 (0.19 0.43)
Group
Radio
Days
17,178 15 (3)
0.27 (0.32)
of males and females, with the expectation that the wider ranging
males would suffer higher mortality rates than the more sedentary
females. Males did suffer higher mortality rates (Table 3-9),
but the differences were not statistically significant (p>0.05).
Reproduction
Information on reproduction on Goldhead was restricted to
the capture of a nestling male fox squirrel. At the time of its
capture on 2 February, 1990, it weighed 100 grams, its dorsal
surface was furred, and its eyes were closed. The squirrel was
estimated to be about 3 weeks old based onthese characteristics.
By back-dating and assuming a 45-day gestation period (Flyger and
Gates 1982), the squirrel would have been conceived in the last
week of November 1989 and born in the second week of January
1990.
Five litters were found on the Fort White area (Table 3-10).
All were in leaf nests in oaks. There were 2-3 young/litter. By
back-dating, three of the litters were conceived in the period 31
May 4 August and the other two litters in the period 15
December 2 February.
The summer breeding season on Fort White began as early as
17 April, based on observations of an adult male chasing an adult
female on that date, and extended until 4 August, based on the
back dating of one litter. The winter breeding began as early as
12 October, based on observations of an adult male pursuing an
adult female on that date, and extended until 2 February, the
estimated date of conception for one of the litters handled.
Radio-collared males on Fort White expanded their home
ranges during the breeding seasons, when some were located about
Table 3-10.
Date
Examined
26 Feb 92
10 Apr 91
Fox
1*
squirrel litters found in nests
Young Sex Weight(g)
on the Fort
Estimated
Age
28 days
21 days
2M:1F
White study
Estimated
Birthday
29 Jan 92
20 Mar 91
area.
Estimated Date of
Conception
15 Dec 91
2 Feb 91
5 Aug 92
19 Aug 93
9 Oct 92
OM:2F
1M:2F
1M:2F
110/each
150/each
150/each
21 days
21 days
21 days
15 July 92
29 July 93
18 Sept 92
31 May 92
14 June 93
4 Aug 92
Table 3-11. Litter frequency for female fox squirrels monitored
on the Fort White study area. A "Y" indicates there was evidence
that a litter was born during the breeding season. A "N"
indicates there was no evidence a litter was born.
1991
1992
1993
Animal #
F010
F140
F120
Winter Summer Winter Summer Winter Summer
F100
F260
F270
F099
F429
4Y:1N 1Y:3N 4Y:1N
Total 3Y:2N
2Y:3N 1Y:3N
80
1.0 km outside of their normal home ranges. Females remained in
their normal home ranges during the breeding season. This is the
normal fox squirrel breeding pattern (Koprowski 1994). Seven
radio-collared males were observed on one occasion clustered
within 50m of a radio-collared female. All of the males were 0.5
to 1 km outside of their normal home ranges.
The frequency of litters for adult females on Fort White
appears in Table 3-11. Sufficient data were available to
evaluate the productivity of these females for 28 reproductive
periods. Litters were produced in 15 of the 28 potential
reproductive periods. The females averaged about one
litter/year. Nine of the 15 litters were born in the summer
period and six in the winter period.
Scent Marks
Fox squirrels often were seen climbing trees with their
noses to the trunk or limb, apparently sniffing the bark as they
traveled. They also were seen rubbing their faces on the bark, a
method fox squirrels use to scent mark (Benson 1980).
Adult male fox squirrels were seen on three occasions
rubbing their faces on trees in spots where the outer bark had
been chewed away. Two of the squirrels first bit at the spot
before they rubbed their faces on the tree. In one instance, the
squirrel pressed his abdomen to the mark point after he had
.rubbed his face on it. The points were on the trunk but
immediately under an overhanging branch or knot and sheltered
from rain. One of the marked trees was a southern red oak (Q.
falcata). This tree had at least four different spots marked.
The spots ranged in size from about 5 by 15 cm to 10 by 30 cm.
All were under the lower most branches on the tree and clearly
visible from the ground. The highest mark seen was about 10m
above the ground. The other two trees where males were seen
marking were pecans. Additional marks were seen on laurel oaks
and live oaks. No effort was made to systematically survey the
study area for mark trees, however, mark trees were observed
scattered across the study area. Similar marking behavior and
mark points have been observed in other studies; both gray
squirrels and fox squirrels have been observed exhibiting this
behavior (Taylor 1968, 1976; Koprowski 1993).
Density
Ten fox squirrels were sighted on the Goldhead study area
during two months of intensive field work in January and-
February, 1990. A 95 ha portion of the study area was trapped
more intensely than any other, and, within this area, seven
adult-sized fox squirrels were sighted. Five of the seven were
captured and radio collared. The collared squirrels restricted
most of their activity to the 95-ha area, and it is assumed the 2
uncollared fox squirrels did also. The minimum fox squirrel
density for this 95-ha area is therefore 7.4 fox squirrels/km2.
This was the best quality fox squirrel habitat in the study area,
and based on sightings and trapping results, it contained the
highest density of fox squirrels.
The primary Fort White study area was 2.3 km2; 27 fox
squirrels lived on the area in April-May 1993: 20 were radio
collared (11 adult males, 5 adult females, 1 subadult male, 3
subadult females); two were ear-tagged only (both subadult
females); and five were unmarked (age and sex unknown). The
unmarked squirrels were assumed residents. The density was
therefore 11.7 fox squirrels/km2.
Fox squirrels on Fort White restricted most of their
activity to the wooded portions of the study area, an area of
49.3 ha. This was their primary habitat. Their density in the
wooded areas was or 54.8 fox squirrels/km2.
Estimates of fox squirrel density from this and other
studies appear in Table 3-12. Density estimates for the
southeastern Coastal Plain range from 5 39 fox squirrels/km2.
This compares to an estimated density for a study area in
Illinois of 153-314 fox squirrel/km2. The striking difference in
densities between the southeast and midwest is believed due to
habitat quality. Even the best fox squirrel habitat in the
Coastal Plain is of marginal quality compared to the habitat in
the midwest.
Foods
Anecdotal observations were made on food habits of fox
squirrels on the Fort White area. They are reported only because
there is little information on the food habits of fox squirrels
in the southeast. The following items were eaten by fox
squirrels on the Fort White area (the season the items were eaten
follows the item): acorns (WI,SP,SU,FA); newly emergent
herbaceous growth (WI,SP); hardwood buds (WI,SP); oak flowers
(SP); mushrooms (WI,SP,SU,FA); mistletoe (Phoradendron serotinum)
berries (WI); field corn (FA); pecans (WI,SU,FA); jelly fungi
(Auricularia sp.) (WI); peanuts (WI,SU,FA); black cherries (SU);
lichens (SU,WI); longleaf and slash pine seeds (SU,FA); magnolia
(Magnolia grandiflora) fruit (SU); and oak galls (FA). Though
Table 3-12. Density estimates for fox squirrels.
Reference
Weigl et al.
1989
This study
Humphrey et
al. 1985
This study
Kantola 1986
Tappe et al.
1993
Moore 1957
Larson 1990
Nixon et al.
1986
Benson 1980
Location
North Carolina
Florida
Goldhead
Florida
Putnam County
Florida
Fort White
Florida
Putnam County
Georgia
Florida
Putnam County
Virginia
Illinois
Method
Nest Count
Complete
Count
Line
Transect
Complete
Count
Nest Count
Captures
Complete
Count
Captures
Captures
Density
Squirrels/km2
5
7.4
8.4
11.7
12.3
15.3-17.7
38
39
153 314
Illinois Sightings
720-1,000
not observed, fox squirrels also may have eaten wild grapes
(Vitus sp.) and blackberries; both fruits were common on the area
in the summer. Evidence of squirrels eating pear seeds was
found, but the sign could have been that of gray squirrels.
Fox squirrels were seen caching food items on 10 occasions.
Food caching was also observed in Florida by Moore (1957) and
Jodice (1990). The items cached on the Fort White study area
were pecans, acorns, peanuts, and, in one instance, an immature
puff ball (Order Lycoperdales). On one occasion I observed a fox
squirrel moving a pecan and an acorn that had been cached
previously. The items were reburied about 7m from where they
were previously cached.
It is common knowledge that squirrels cache food items, and
it was only mentioned here because of speculation that
southeastern fox squirrels do not cache foods (Loeb and Moncrief
1993). Fox squirrels in Florida cache foods, but perhaps less
frequently than fox squirrels in other areas. The infrequency of
the behavior may have caused other researchers in the southeast
to miss it, thus leading to the statements made by Loeb and
Moncrief (1993).
Fox squirrels supplemented their diet with peanuts and corn.
The importance of these crops varied by year and by squirrel.
Peanuts, for example, were planted on a 2-4 year rotation. They
grew as volunteers in the off-years, but they were only abundant
in the years when planted. Fox squirrels ate the crops available
within their home range, but there were no observed instances of
fox squirrels traveling outside of their normal home range to
exploit crops.
85
Pine trees were uncommon on the Fort White study area, and
although the squirrels ate the pine mast that was available, it
was a minor component of their diet. This contrasts to the
Goldhead study area and other areas in the Coastal Plain were
pine mast was a critical component of the summer and early fall
diet (Kantola 1986, Weigl et al. 1989). Fox squirrels on the
Fort White area successfully substituted other foods for pine
mast.
Concluding Discussion
In the past 10 years, our knowledge of fox squirrel
population ecology in northern Florida has increased
considerably, both with the study reported here and with the work
of Kantola and Humphrey (1990). Prior to these studies, our
knowledge of fox squirrel biology in northern Florida was based
primarily on a two year study conducted in the 1940s (Moore
1957). In some aspects, the new information has changed our
understanding of fox squirrels, whereas in other areas additional
study has only strengthened Moore's (1957) conclusions. I have
tried to summarize our knowledge of fox squirrel biology in
northern Florida in the discussion that follows. Sample sizes
remain small for many aspects of their biology, and our knowledge
remains limited. However, we know more than we did. When
necessary, I have compared and contrasted the Florida
observations to those made on fox squirrels in other parts of the
species's range in an attempt to clarify the discussion.
Mortality
The only data on fox squirrel predation for northern Florida
were the observations reported earlier from the Fort White study
86
area. The important predators on the Fort White study area were
raptors, canids, and bobcats. This probably applies throughout
the state, but other predators, such as great horned owls (Bubo
virginianus), gray and red foxes (Vulpes vulpes), rattlesnakes,
and domestic dogs, may be locally important predators on fox
squirrels. Moore (1957) considered that bald eagles might be a
significant predator of fox squirrels. This seems unlikely.
Eagles are relatively uncommon, they tend to hunt around lakes or
scavenge along highways (Wood 1992), and because of these traits,
I doubt if they encounter fox squirrels often enough, or are
proficient enough at hunting them, to be an important predator.
Human predation on fox squirrels may have been significant
in the past, but interest in fox squirrel hunting in Florida has
been low in recent times (Wooding 1990). The lack of interest
was one of the factors which lead to the season closure on fox
squirrels in northern Florida. This took affect beginning with
the 1996-97 season. Fox squirrels were legal game on Fort White
study area during the time of the field work, but no one hunted
them.
A number of fox squirrels on the Fort White study area were
killed by vehicles while crossing S.R. 47, a two-lane highway
that formed the western border of the study area. Roadkill
mortality was not observed on the Goldhead study area, and it was
not mentioned by Moore (1957) or Kantola and Humphrey (1990).
There may be areas in Florida where roadkill mortality is so
severe that it limits fox squirrels, such as in urban areas or
subdivisions with a high road density, but these conditions did
not exist on any of the northern Florida study areas.
87
The only data available on mortality rates for Florida were
obtained on the Fort White study area. The annual mortality rate
of radio collared squirrels was about 30%. The rate included
mortality by vehicles and predators. Similar rates were observed
by Hansen et al. (1986) for an unhunted fox squirrel population
in Illinois. Moore (1957) had speculated that predators would
only kill an occasional fox squirrel. The Fort White data
supported his suspicions. Weigl et al. (1989) believed that
coastal plain fox squirrels were too rare to become a major food
item, and as a result, no predator could afford to hunt
specifically for them.
Before concluding this section on mortality, I want to
comment on one of Moore's (1957) observations on fox squirrel
behavior. He reported several incidents in which fox squirrels
that were fleeing for their lives ran down gopher tortoise
(Gopherus polyphemus) burrows. Moore (1957) believed that the
behavior was common, but it was not observed by myself or Kantola
and Humphrey (1990). My interpretation of the events Moore
(1957) described were of desperate animals taking desperate
actions, and I believe if given a choice between a tree or a hole
in the ground, a fox squirrel will tree every time. While there
are a number of species that depend on gopher tortoise burrows
for their survival, the data suggest that fox squirrels are not
one of them.
Reproduction
Moore (1957) identified 2 breeding seasons per year for fox
squirrels, a pattern that is consistent throughout the species
range (Koprowski 1994). The first data for the state on litter
88
frequency was collected at Fort White. Several females produced
two litters per year, but the overall litter frequency was 1 per
year. Similar litter frequencies have been observed elsewhere
(Harnishfeger et al. 1978).
Knowledge of litter size in northern Florida is based on a
sample of 17 litters; 11 were examined by Moore (1957), and six
were examined in the current study). Litter size ranged from 1
to 4, with a mean of 2.3. Fox squirrels usually have 2-3 young
per litter throughout their range (Koprowski 1994).
Weigl et al. (1989) studied fox squirrel reproduction in
coastal North Carolina in habitat similar to that found in
northern Florida. He reported rather emphatically that the
winter breeding season was the major period of reproduction. His
data were based almost exclusively on examinations of nest boxes.
In Florida, data are available on the period of birth for 27
litters; 11 in Moore (1957) and 16 in this study. Fourteen of
the litters were born in the winter breeding season, and 13 in
the summer season. Only one of the Florida litters was found in
a nest box, and it was a winter litter. I believe that the
Florida data more accurately represent the breeding
characteristics of fox squirrels, and until further data show
otherwise, that the two breeding seasons are of equal importance.
I believe the North Carolina observations (Weigl et al. 1989)
were biased by their study methods. Fox squirrels use nest boxes
mainly during cold weather (Nixon et al. 1989), and I think the
summer litters were missed because they were not checking leaf
nests.
Nesting Habits
Much of Moore's (1957) field effort was spent in studying
fox squirrel nesting habits. Among other observations, Moore
(1957) concluded that leaf nests were used more often than were
tree cavities. This conclusion was also reached by Kantola and
Humphrey (1990). My observations are largely anecdotal, but they
support the other studies. I can only remember 4 occasions when
I located a radio collared fox squirrel in a tree cavity,
compared to hundreds of locations when the squirrels were in leaf
nests.
Edwards (1986) believed that litters born in tree cavities
were safer from predators than those born in leaf nests. This is
probably true, and even though nest predation was suspected at
Fort White, there are no indications that the availability of
cavities limits fox squirrels in Florida. Kantola and Humphrey
(1990) observed abundant cavities on their study area, yet they
observed little cavity use. Cavities may be needed at times in
northern areas as a thermal refuge, but Florida winters are mild
and it is unlikely that cavities are needed for warmth. The
conclusion of this is that cavities, or artificial cavities such
as nest boxes, are not a necessary component of fox squirrel
habitat in Florida.
Normally when we think of cavities for a tree squirrel, we
think of above ground cavities in standing trees. Moore (1957)
made a number of unusual observations on his study area, one of
which was of fox squirrels nesting in tree stumps. He found 5
such underground dens. I never saw this behavior, nor did
Kantola and Humphrey (1990), and nor have any other studies with
90
which I am familiar. It thus seems, based on the evidence, that
underground nesting is not a common event in fox squirrels. This
topic was mentioned because of a current debate underway among
management area biologists over the value of pine stumps for
wildlife in northern Florida. For fox squirrels at least, pine
stumps do not appear to be a limiting factor, and the removal of
the stumps for the turpentine they contain will not impact fox
squirrels.
Food Habits and Habitat Use
There have been no detailed studies of fox squirrel food
habits in northern Florida. However, certain conclusions can be
reached with the data that are available. One conclusion is that
acorns are probably a major component of the diet. Important oak
species include live oak, turkey oak, southern red oak, and
laurel oak. No research has been conducted in xeric flatwoods
habitat on fox squirrels, however, the runner oaks (Q. minima and
Q. pumila) may be an important source of acorns.
The importance of a particular species will vary with its
abundance and the quantity of seeds it produces. Moore (1957)
believed that turkey oak was a major producer of acorns, but
Umber (1975) demonstrated that turkey oak only occasionally
produces large quantities of mast. In an average year in
sandhill habitat, live oak may be more important than turkey oak
(Kantola and Humphrey 1990).
Pine mast is another important food for fox squirrels in
northern Florida. In certain habitat types, such as longleaf
sandhill, longleaf pine seeds are a primary summer food (Moore
1957, Kantola and Humphrey 1990). Fox squirrels will also eat
the seeds of other pines. I have seen them eat seeds from
loblolly, slash, and sand pine. My impressions are that fox
squirrels relish pine seeds, which are an energy rich source of
food (Weigl et al. 1989). However, if other foods are available,
fox squirrels can survive in northern Florida without pine mast.
Mast bearing pines were rare on the Fort White area, and although
fox squirrels ate the pine mast that was available, they
subsisted on other foods in the summer.
Under most conditions, oak and pine seeds appear to be the
staple foods of fox squirrels in northern Florida. Other foods
that may be seasonally or locally important include leaf buds,
oak flowers, row crops, pecans, and wild fruits, such as black
cherries.
Fox squirrels also ate a mystery food on the Fort White
study area. I often saw fox squirrels eating items which they dug
from the ground. The foods were occasionally acorns, but on a
number of occasions, the foods were not acorns or other nuts. I
was never able to identify the food, but it was darkly pigmented
and appeared to be soft in texture because they ate it with
minimal chewing. My suspicions were that it was the fruiting
body of a subterranean fungi. Weigl et al. (1989) suggested that
fungi may be an important food item for fox squirrels in the
southeastern coastal plain.
Habitat Use and Quality
Fox squirrels in northern Florida are normally associated
with mature longleaf pine forests. As discussed in Chapter 2, my
impressions are that it is not the pines that draw the squirrels,
but it is the structure of the habitat. Fox squirrels are
especially adapted for life in wooded savannahs (Nixon et al.
1984, Weigl et al. 1989). The savannahs occupied by fox
squirrels in Florida are pine dominated, whereas those occupied
in the midwestern United States are hardwood dominated. The
longleaf savannah is the natural habitat of the fox squirrel in
Florida, and still the animal's predominate habitat. Fox
squirrels have adapted to man-made savannahs, such as those found
on the Fort White study area, demonstrating that it is not the
pines but the structure. Longleaf pine forests just happen to be
the most common forests in northern Florida with the required
structure.
Fox squirrel studies conducted in northern Florida have
revealed that fox squirrels here occur at low densities and
occupy the largest home ranges determined for the species. In
comparison to Florida, fox squirrel densities in the midwestern
United States were up to 90 times greater than those in Florida
(Table 3-12), and home ranges have been observed there that were
90% smaller than those in Florida (Adams 1976).
Difference in carrying capacity and reproductive potential
between the midwest and Florida can be clearly demonstrated by
comparing data collected on the Fort White study area to that
collected on a study area in Illinois (Hansen et al. 1986). If
we assume a litter frequency of 1/year, an average litter size of
2.5 for both study areas, and use the adult female density
estimates of 77/km2 for Illinois and 2.2/km2 for Fort White, the
annual production of offspring per km2 is 192 for Illinois and
5.5 for Florida.
Differences in fox squirrel abundance between Florida and
the midwest are believed a consequence of differences in the
abundance of hardwood seeds. Midwestern savannahs contain an
assortment of hardwood tree species that produce highly
digestible, energy rich seeds that are easily stored, or cached
for later use (Nixon et al. 1968, Korschgen 1981). The best
seeds in terms of energy and digestibility are hickories (Carva
sp.) and black walnuts (Juglans niger) (Smith and Follmer 1972,
Havera and Smith 1978).
Florida pine savannahs typically contain a low diversity of
mast producing species. Pine seeds are one of the richest foods
produced in the habitat (Weigl et al. 1989), but they are only
available for about 4 months of the year, and they are not
storable. Oaks are the primary hard mast producer in Florida fox
squirrel habitat. Acorns are lower in calories and less
digestible than hickories and walnuts (Havera and Smith 1979).
Acorns also have less storage potential than the other seeds,
which limits the period they are available as a food source.
Smith and Follmer (1972) have shown the nutritional value of
acorns decreases after germination. Acorns of the white oak
group, which includes live oak, tend to germinate soon after
falling, which makes them undesirable for storage. Acorns of the
red oak group, such as turkey oak, have delayed germination,
which would increase their value for caching. However, Florida's
winters are mild, which could lead to quicker germination of
these seeds, thus decreasing the length of time they are
available. These factors relating to seed storage may be the
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