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2012 SOUTHEASTERN NATURALIST 11(3):517–528
Denning Ecology of Florida Black Bears in
Elina P. Garrison1,*, J. Walter McCown1, Mark A. Barrett2, and Madan K. Oli3
Abstract - We studied the denning chronology, den type, and den-site characteristics of
Ursus americanus floridanus (Florida Black Bear) in Ocala National Forest (ONF) and
the adjacent residential area of Lynne, FL. We monitored 35 radio-collared females for
62 den years from 1999 through 2003. Den entry dates did not differ between parturient
females (females that gave birth to cubs during the winter) and nonparturient (solitary
females or females with yearlings) (P = 0.139). Females with cubs exited dens later (P less than
0.001), and denned longer (mean =113 ± 3.3 days) than females without cubs (mean = 54
± 6.0 days; P < 0.001). Among females with cubs, primiparous females entered dens on
average 28 days later than multiparous females (P = 0.003); however, exit date and duration
of denning did not differ between the two groups. Female bears denned in ground
nests most frequently (n = 45), followed by excavated dens (n = 7); one female used a
tree den. Compositional analysis revealed that denning habitat selection occurred in ONF,
with sand pine as the preferred denning habitat, followed by swamp and pine flatwoods
habitats. Denning habitat selection was not evident in Lynne, although the majority of females
denned in swamp habitats. Parturient females often denned in ecotones with dense
vegetation, due perhaps to the fact that such ecotones offer better protection to the female
and her cubs from potential predators and weather elements. Habitat management activities
should be limited during peak denning of parturient females, from late December to
mid-April, particularly in Sand Pine - xeric oak and pine flatwood - swamp ecotones.
Denning, or winter dormancy, in bears is thought to have evolved in response
to seasonally occurring periods of adverse weather conditions and lack
of food resources (Hayes and Pelton 1994). Denning is obligatory for parturient
females, as birth and early maternal care of altricial young occur during
winter dormancy (Alt 1983, Hellgren 1998). Denning is not, however, obligatory
for all bears. In North American Ursus maritimus Phipps (Polar Bear) and
some U. arctos L. (Brown Bear) populations, males may remain active during
all or part of the winter if sufficient food is available (Ramsay and Stirling
1988, Van Daele et al. 1990). In the southern range of U. americanus Pallas
(American Black Bear), adult and subadult males and some nonparturient females
may remain active during all or part of the winter (Dobey et al. 2005,
Graber 1990, Hellgren and Vaughan 1989, Mitchell et al. 2005, Weaver and
Pelton 1994, Wooding and Hardisky 1992).
1Florida Fish and Wildlife Conservation Commission, 1105 SW Williston Road, Gainesville,
fl32601. 2Florida Fish and Wildlife Conservation Commission, Koger-Marathon,
2574 Seagate Drive, Tallahassee, fl32301. 3Department of Wildlife Ecology and
Conservation, University of Florida, 110 Newins-Ziegler Hall, Gainesville, fl32611.
*Corresponding author - email@example.com.
518 Southeastern Naturalist Vol. 11, No. 3
While denning, particularly in northern latitudes, bears cease ingressive and
eliminative functions and are in a lethargic state or deep sleep (Nelson et al.
1983). Disturbance during this period, particularly disturbance of females with
cubs, can diminish fitness by increasing energy expenditure and may cause cub
abandonment (Alt 1984, Elowe and Dodge 1989, Linnell et al. 2000, Oli et al.
1997). The period with potential for disturbance to denning bears varies by region
because den entry and exit dates as well as duration of denning may vary
regionally (Johnson and Pelton 1980, Smith et al. 1994). Types of dens used by
Black Bears also vary considerably among populations, because different habitats
provide different denning options (Hayes and Pelton 1994, Johnson and Pelton
1981). Thus, population-specific knowledge of denning habitat requirements and
chronology is necessary for formulating appropriate management strategies for
Black Bears (Hightower et al. 2002).
Ursus a. floridanus Merriam (Florida Black Bear), a threatened subspecies
of the American Black Bear, historically inhabited all of Florida (Brady and
Maehr 1985, Maehr et al. 2001). However, unregulated hunting in the 1800s
to 1970s and loss and fragmentation of habitat substantially reduced the range
of Florida Black Bears (Brady and Maehr 1985). Currently, the Florida Black
Bear exists in 7 relatively isolated populations that exhibit limited connectivity
(Dixon et al. 2007, Eason 2000). Conservation of the remaining populations of
the Florida Black Bear requires a thorough understanding of the local ecological
requirements, including for denning; however, limited data are available for
this subspecies (Seibert 1995, Wooding and Hardisky 1992). We therefore investigated
denning ecology of female Florida Black Bears in Ocala National
Forest (ONF) and the adjacent residential area of Lynne, in north central Florida
(Fig. 1). Specifically, we investigated denning chronology, determined den types
used, and tested for the selection of macroscale denning habitat by Florida Black
Bears in north-central Florida.
Ocala National Forest covers more than 1740 km2 and supports the core habitat
for the largest Black Bear population in Florida (Simek et al. 2005). ONF is
bounded to the west and north by the Ocklawaha River and to the east by the St.
Johns River. Our study area covered the central portion of ONF and an adjacent
residential community of Lynne, and encompassed approximately 760 km2 (520
km2 in ONF and 240 km2 in Lynne; Fig. 1).
The vegetation in ONF was dominated by a central ridge with a Sand Pine–
scrub oak community, dominated by Pinus clausa Chapman ex Engelm. (Sand
Pine), Quercus myrtifolia Willd. (Myrtle Oak), Q. geminata Small (Sand Live
Oak), and Q. chapmanii Sarg. (Chapman Oak). Other major vegetation types in
ONF included swamps and marshes along the Ocklawaha and St. Johns rivers,
pine flatwoods between the rivers and central ridge, mixed hardwood swamps,
and numerous lakes, ponds, and prairies (Aydelott et al. 1975). Pine flatwoods
were dominated by P. elliottii Engelm. (Slash Pine), with scattered bays such as
2012 E.P. Garrison, J.W. McCown, M.A. Barrett, and M.K. Oli 519
Magnolia virginiana L. (Sweetbay Magnolia) and Gordonia lasianthus (L.) Ellis
(Loblolly Bay). In addition to the scrub oaks, common shrub species included
Figure 1. Map of Ocala National Forest (ONF) displaying the ONF and Lynne study areas
(thick-line polygons) within which Black Bear dens were located. Land-cover classes are
grayscale or patterned. Inset map depicts geographic location of the study area in northcentral
520 Southeastern Naturalist Vol. 11, No. 3
Sabal etonia Swingle ex Nash (Scrub Palmetto) and Ceratiola ericoides Michx.
(Florida Rosemary). In wetter areas, Serenoa repens (Bartman) Small (Saw Palmetto)
and Lyonia ferruginea (Walter) Nutt (Fetterbush) were common.
ONF is managed with an ecological approach to achieve multiple-use management
that results in a healthy ecosystem while meeting the needs of people,
including outdoor recreation (United States Department of Agriculture 1999).
Sand Pine is harvested to regenerate scrub to early successional conditions, with
stand age ranging from recently harvested clear-cuts to stands ≥20 years. ONF
receives more visitors than any other national forest in Florida (US Forest Service
2010). With the exception of 4 designated wilderness areas, ONF contains
off-road-vehicle and logging roads, forest trails, and an extensive grid of roads
maintained by the US Forest Service. Natural habitats in Lynne mainly consisted
of swamp forest, pine flatwoods, marsh, and Sand Pine. However, compared to
ONF, Lynne habitat was highly fragmented by roads and residential and commercial
developments (Hostetler et al. 2009).
We captured bears during July 1999–May 2003 with Aldrich spring-activated
foot snares (Johnson and Pelton 1980) modified for safety (Scheick et al. 2009).
We immobilized captured bears with a 1:1 mixture of tiletamine hydrochloride
and zolazepam hydrochloride (Telazol®) administered at 3.0–4.5 mg/kg (adapted
from Taylor et al. 1989) of estimated body weight via CO2-charged dart delivery
system (Model 1V.31NPL, Telinject, Victoria, Australia). We fitted all adult
female bears with a VHF motion-sensitive radiocollar (Telonics, Mesa, AZ).
Collars had a leather breakaway connector that allowed them to fall off after
approximately 2–3 years (Seibert and Wooding 1994). We lip-tattooed and eartagged
bears for identification, extracted a 1st premolar to determine age (Willey
1974), collected standard morphometric data, and determined reproductive status
(Garrison et al. 2007, McCown et al. 2009). Bears were handled in a humane
manner, and all procedures complied with guidelines of the American Society of
Mammalogists (Animal Care and Use Committee 1998) and had been approved
by the University of Florida’s Institutional Animal Care and Use Committee
(protocol # A707).
We located radiocollared bears 1–7 days a week from the ground via standard
triangulation methods (White et al. 2001) and from a Cessna 172 aircraft equipped
with wing-mounted antennas. We classified bears as denning when successive telemetry
locations during the denning season were <400 m apart. Denning status
and den location (if the bear was indeed denning) were subsequently verified by
approaching the den using handheld telemetry equipment during January and
February 1999–2003. To minimize disturbance to the denning bears, we quietly
clipped a trail with small pruning shears through the vegetation as we approached
the den site.
We estimated den entry date as the midpoint between the last date of
recorded movement and the first date at the den (Oli et al. 1997). Den
2012 E.P. Garrison, J.W. McCown, M.A. Barrett, and M.K. Oli 521
emergence date was defined as the midpoint between the last location of a
bear in the den and the first location of that bear away from the den (O’Pezio
et al. 1983). Duration of denning was defined as the period between the entry
and exit dates; this definition was used even when a bear moved a den
(e.g., due to disturbance), as long as location did not change after the move.
We classified females into 2 categories based on their reproductive status:
(1) parturient (females that gave birth to cubs during the winter) and (2) nonparturient
(solitary females and those with yearlings). Parturient females were
further classified as either primiparous (first-time mothers) or multiparous
(females that had given birth previously) based on physical characteristics of
the female at capture (lactating, characteristics of teats indicating previous
nursing) or presence of cubs or yearlings (at capture or through remote camera
photos). We used the Kruskal-Wallis test to compare den entry and exit
dates, and duration of denning with respect to year, reproductive status, and
reproductive experience (primiparous or multiparous).
Den sites were examined after bears emerged. We obtained Universal Transverse
Mercator (UTM) coordinates of den sites with a Garmin eTrex (Garmin
International, Olathe, KS) global positioning system (GPS). We classified dens
as ground nests, excavations, or tree dens, measured den dimensions, and noted
non-quantitative, descriptive characteristics of the den surroundings.
Several studies have shown that female Black Bears do not select den sites
at random (Hayes and Pelton 1994, Johnson and Pelton 1980, Klenzendorf et al.
2002, Oli et al. 1997), and it is important to consider both use and availability to
understand selection of den sites (Reynolds-Hogland et al. 2007); therefore, we
tested for denning habitat selection using compositional analysis (Aebischer et
al. 1993). We used a geographic information system (GIS; ArcMap 9.2, ESRI,
Redlands, CA) to aid in estimating use and availability. Land-cover types were
represented by a 30-m resolution, digital land-cover layer created at a statewide
scale for Florida (Kautz et al. 2007; see Gilbert and Stys 2004 for a detailed
description of land-cover types). Twenty-four land-cover types occurred within
each study area, but were reclassified into 6 habitat types for our analysis (Fig. 1)
because most were analogous types or scarce in the study areas. The 6 habitat
types were Sand Pine, xeric oak scrub, pine flatwoods, marsh, swamp forest, and
other (Table 1). To assign dens to habitat type, we used the GIS to intersect the
habitat-type layer with den-site locations. Furthermore, each forest cover type
was verified with field observations during den visits. We estimated use as the
proportion of dens in each habitat type. We generated 95% minimum convex
polygon (MCP) home ranges from telemetry location data (mean locations/bear:
ONF = 41, Lynne = 38) for each female bear for every den year. The percentage
area of each habitat type within an MCP was considered the availability of that
habitat type. However, for individual bears with multiple den years, we summarized
percentage habitat availability over their multiple MCP areas. We therefore
considered each bear, rather than each year, as an experimental unit. Annual
home-range size (MCP areas) ranged from 4.89 to 98.77 km2 for ONF and from
3.45 to 39.6 km2 for Lynne.
522 Southeastern Naturalist Vol. 11, No. 3
A compositional analysis was conducted for ONF females (n = 18) and for
Lynne females (n = 11). First, we used a MANOVA to test the null hypothesis
that habitat selection did not occur. If the null hypothesis was rejected, we compiled
a ranking matrix where selection (or lack thereof) for each habitat type was
compared with that for all other habitat types. Significance of pair-wise comparisons
of habitat selection was based on randomization tests with 10,000 runs, as
described by Aebischer et al. (1993). If a habitat was available but not used, we
replaced the missing value with a small positive number (0.01) to avoid computational
problems (Aebischer et al. 1993).
During 1999–2003, we monitored 35 females for 62 den years. We determined
denning chronology for 38 parturient den years, and 18 nonparturient den years.
Six nonparturient females remained active through the winter. Den entry dates
did not differ between parturient and nonparturient females (χ2 = 2.19, d.f. = 1,
P = 0.139). Parturient females exited dens later (χ2 = 34.7, d.f. = 1, P < 0.001),
and denned longer (mean ± SE = 113 ± 3.3 days) than nonparturient females (54
± 5.7 days; χ2 = 30.28, d.f. = 1, P < 0.0001; Table 2). Den entry and exit dates of
parturient females differed among years (χ2 = 12.3, d.f. = 3, P = 0.006; χ2= 14.4,
Table 1. Habitat availability and use for Florida Black Bears denning in Ocala National Forest
(ONF) and Lynne, FL. Percentage availability (A%) is the mean (± SE) percentage cover of each
habitat type that occurred within the home range (95% minimum convex polygon) of female bears
with dens in ONF (n = 18) and Lynne (n = 11). Percentage use (U%) is the percentage of dens (n =
25 for ONF and n = 11 for Lynne) that occurred in each habitat type. Land-cover type is based on
a statewide, 30-m-resolution digital land-cover layer (Kautz et al. 2007); some cover types were
combined because they were analogous types or scarce.
Habitat type A% ± (SE) U% A% ± (SE) U% Land-cover type
Sand Pine 52.2 (3.8) 56 8.9 (4.1) 0 Sand Pine
Xeric oak scrub 23.3 (1.3) 8 n/aA n/a Xeric oak scrub
Pine flatwoods 1.1(0.3)B 8 28.6 (4.2) 18 Pinelands
Swamp forest 4.8 (1.3) 24 29.5 (2.8) 64 Shrub swamp, hardwood swamp, bay
swamp, cypress swamp, mixed wetland
Marsh 8.6 (4.2) 4 9.8 (2.7) 9 Freshwater marsh and wet prairie, open
Other 10.1 (1.1) 0 22.8 (2.1) 9 Sandhill, dry prairie, mixed pine–hardwood
forest, hardwood hammock and forest,
shrub/brushland, grassland, bare soil/
clearcut, high- and low-impact urban,
improved and unimproved pasture,
AXeric oak scrub was added to the “other” class for Lynne due to the small percentage composition
(2.5%) and availability to only a few female bears.
BAlthough pine flatwoods had a small percentage composition in ONF, it was available to all female
bears in ONF.
2012 E.P. Garrison, J.W. McCown, M.A. Barrett, and M.K. Oli 523
d.f. = 3, P = 0.002), but duration of denning did not (χ2 = 4.8, d.f. = 3, P = 0.187).
Among parturient females, primiparous females entered dens on average 28 days
later than multiparous females (χ2 = 8.71, d.f. = 1, P = 0.003). However, exit date
and total denning period did not differ between these 2 groups (χ2 = 3.27, d.f. =
1, P = 0.07; χ2= 1.53, d.f. = 1, P = 0.22). Den exit and entry dates, or duration of
denning of nonparturient females did not differ among years (Table 2).
We located 53 dens, of which 42 (79%) were used by parturient females
and 11 by nonparturient females. Solitary females and females with yearlings
typically left the den when approached, making location of these dens difficult.
Thirty-four (81%) of the parturient females denned in ground nests, 7 (17%)
denned in excavations, and 1 (2%) female used a tree den. All nonparturient
females denned in ground nests. Ground nests were typically oval, and dimensions
averaged 71 × 56 × 23 cm (length × width × depth). Bedding material
consisted of dry leaves, pine needles, or other dry litter available in the habitat.
Dimensions of the excavated dens averaged 96 × 74 × 100 cm (height × width ×
depth), and all but 2 excavated dens were in sandy soil. Entrances to excavated
dens were half moon–shaped and typically contained very little bedding material,
such as dry leaves, on top of the sand. The only bear that used a tree den was
a 10-year-old female with a litter of 3 cubs. The den tree was a Nyssa sylvatica
Marsh (Black Gum). In ONF, dens were located in all habitat types except
“other” (Table 1). Compositional analysis revealed that den-site selection was
Table 2. Denning chronology of female Florida Black Bears in north-central Florida. Den entry
dates, emergence dates, and duration of denning are given for each year and for all years pooled,
by reproductive status (parturient, nonparturient) and, for pooled years, reproductive experience
Den entry Den exit Duration of denning
Group Mean SE n Mean SE n Mean SE n
Parturient 19 Jan 4.5 8 28 Apr 3.5 7 103 4.1 7
Nonparturient -A - -
Parturient 18 Dec 6.3 10 12 Apr 1.8 8 114 6.9 8
Nonparturient 1 Jan 5.9 12 1 Mar 3.7 12 61 6.4 12
Parturient 19 Dec 5.4 11 14 Apr 3.3 12 116 6.2 11
Nonparturient 29 Jan 9.8 3 12 Mar 5.0 3 43 9.9 3
Parturient 2 Jan 7.8 8 1 May 4.7 8 121 4.4 8
Nonparturient 6 Jan 6.2 3 16 Feb 14.0 3 41 20.4 3
Parturient 28 Dec 3.5 37 19 Apr 2.2 35 113 3.3 34
Nonparturient 6 Jan 4.9 18 1 Mar 3.7 18 54 5.7 18
Primiparous 20 Jan 8.7 7 30 Apr 6.8 6 106 8.6 6
Multiparous 23 Dec 3.3 30 17 Apr 2.1 28 116 3.1 27
524 Southeastern Naturalist Vol. 11, No. 3
not random (Wilk’s Λ = 0.11, P = 0.0001), and Sand Pine ranked as the most
preferred denning habitat, followed by swamp forests and pine flatwoods.
Sand Pine was preferred over scrub, marsh, and other, while pine flatwoods
and swamp habitats were preferred over scrub and other. In Lynne, dens were
located in all habitat classes except Sand Pine. The randomization test did not
provide evidence for denning-habitat selection in Lynne (Λ = 0.19, P = 0.114).
Understanding aspects of denning ecology is important for effective management
of Black Bear populations because birth and early maternal care
occur in dens (Hellgren and Vaughan 1989, Linnell et al. 2000). In our study
area, parturient females generally entered dens earlier and denned longer than
nonparturient females, a finding consistent with those of other studies (Kashbohm
et al. 1996, Mitchell et al. 2005, Oli et al. 1997, Schooley et al. 1994,
Wathen 1983). The average duration of denning of parturient females (113
days) and the prevalent use of ground dens recorded in this study are similar
to those reported for other southeastern populations of Black Bears (Dobey et
al. 2005, Hamilton and Marchinton 1980, Hellgren and Vaughan 1989, Martorello
and Pelton 2003, Weaver and Pelton 1994, White et al. 2001, Wooding
and Hardisky 1992). Use of tree dens has also been reported in southeastern
populations of Black Bear (Crook and Chamberlain 2010, Dobey et al. 2005,
Hellgren and Vaughan 1989, Weaver and Pelton 1994, White et al. 2001). In
our study, only one female used a tree den.
Although tree dens or excavated dens likely provide more protection from
weather and disturbance than do ground nests, bears have apparently adapted to
using ground nests by using thick vegetation as a substitute for the concealment
and protection that a tree den or excavated den might provide (Martorello and
Pelton 2003). We speculate that in addition to providing concealment, dense vegetation
surrounding a den site allows females to more easily hear an approaching
predator and therefore serves as a means of warning. It often took us several
hours to reach the den sites within hearing or viewing distance of a female with
cubs; although we took precautions (e.g., only 1 or 2 people would approach the
den, and to reduce noise we clipped vegetation with small pruning shears rather
than break it), we found it difficult to move through the thick vegetation quietly
enough to avoid alerting the denning female. In most cases, the females were
fully awake by the time we were within viewing distance. In contrast, den sites of
females without cubs were more accessible, and it appeared that ease of escape,
greater visibility, and awareness of the surroundings were important factors infl
uencing selection of den sites.
Sand Pine was the most preferred denning habitat in ONF, and it was also the
most abundant habitat type. Swamp forests also were selected for; on average,
swamp forests covered only 5% of the female’s home ranges, yet 25% of the dens
occurred in swamp forests, making it an important denning habitat. The lack of
statistical evidence for denning habitat selection in Lynne may be a consequence
of small sample size. Nonetheless, most (64%) of the dens in Lynne occurred in
2012 E.P. Garrison, J.W. McCown, M.A. Barrett, and M.K. Oli 525
swamp forests. Typical understory vegetation in swamp forests (e.g., Fetterbush,
Ilex glabra (L.) Gray [Gallberry], Smilax spp. [greenbriar]) provides a dense
cover, making it difficult for intruders to approach the den without being noticed.
Many dens were located near habitat edges (or within ecotones). Fifteen of 20
dens used by parturient females in mesic-hydrid habitats occurred in ecotones;
5 of the 20 dens in mesic-hydric habitat were located next to lakes or ponds.
In ONF, the dens occurred in sandpine - xeric oak ecotones in the center of the
forest and near lakes and ponds in the eastern edge of the forest. In Lynne, dens
occurred mainly in the pine flatwoods - swamp forest ecotone. No nonparturient
females denned in ecotones. Whether proximity of dens to habitat edge is a result
of coarse-scale habitat classification, edge effects, or proximity to water, it may
be important to consider ecotones in bear management strategies in addition to
focusing on specific habitat types.
We found no evidence of feeding by parturient females during denning,
whereas most den sites of nonparturient females had evidence of feeding (e.g.,
pulled shoots of Saw or Scrub Palmetto) surrounding the nests. Although activity
during denning is rare in Black Bears inhabiting northern habitats, evidence of
feeding and movement has been reported in other southern Black Bear populations
(Hightower et al. 2002, Pelton et al. 1980).
The Ocala bear population is characterized by low cub survival (Garrison
et al. 2007), and human disturbance of denning bears may further reduce cub
survival. Thus, forest management practices and recreational activities during
the denning season should be planned to minimize disturbance to denning bears.
Specifically, prescribed burning and timber harvesting should be limited between
mid-December and mid-April in habitats suitable for denning, including sand
pine, pine flatwoods, and swamp forest. If prescribed burning or logging is unavoidable,
it should be carried out early in the denning season so that pregnant
females may leave disturbed areas before they have given birth.
The majority of the dens in our study sites were ground nests, and availability
of suitable den sites does not appear to be a limiting factor in the ONF and Lynne.
Although open nests do not provide the thermoregulatory benefits offered by
enclosed dens, dense vegetation can provide structural security and reduce heat
loss from wind (Hayes and Pelton 1994, Hellgren and Vaughan 1989, Ryan and
Vaughan 2004). In the mild winters of northern Florida, however, protection from
weather is probably not as critical as the protection from disturbance afforded
by dense vegetation. Based on results of compositional analysis, and anecdotal
observation (e.g., the difficulty of reaching den sites of parturient females due
to the thick vegetation), it appears that den-site selection is non-random. Further
research is needed to evaluate the microhabitat characteristics of den sites of
females with young of the year.
Our research was funded by the Florida Fish and Wildlife Conservation Commission
(FWC), Florida Department of Transportation, Wildlife Foundation of Florida, African
Safari Club International, Jennings Scholarship, and Department of Wildlife Ecology
526 Southeastern Naturalist Vol. 11, No. 3
and Conservation, University of Florida. Special thanks to M. Cunningham, J. Dixon, M.
Moyer, D. Masters, K. Oven, K. Hanson, C. Long, and E. Merchant for assistance with
all aspects of the fieldwork. We thank FWC pilots J. Wisniesky, J. Johnston, and P. Crippen
for telemetry flights. We also thank T. Eason, M. Sunquist, G. Tanner, D. Onorato, B.
Scheick, and two anonymous reviewers for helpful comments on the manuscript.
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