Biology

Florida Black Bear

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When the American black bear (Ursus americanus) in Florida was first scientifically described in 1896 by naturalist C. Hart Merriam, he thought its long skull and highly arched nasal bones distinguished it from black bears in other areas and classified it as a separate species (Ursus floridanus), which he called the Everglades bear. Subsequent analyses around 1960 revised the status of these bears to the Florida black bear (U. a. floridanus), one of 16 recognized subspecies [1].

 

caption Source: Florida Habitat

 

Conservation Status

 

Scientific Classification

Kingdom: Animalia
Phylum:-- Chordata
Class:---- Mammalia
Order:------ Carnivora
Family:------ Ursidae
Genus:-------- Ursus
Species:-- Ursus americanus Pallas, 1780
Subspecies:-------Ursus floridanus

Description

Black bears are large-bodied and have short tails, prominent canine teeth, and plantigrade feet (the entire foot strikes the ground when walking) each with five digits, and each digit bearing a short, curved, nonretractable claw.  The characteristic gait of the black bear is pacing, a stride in which legs on the same side move simultaneously so that the hind foot is placed in or slightly in front of the track of the forefoot. Unlike humans, the smallest toe of each foot is the inner toe and occasionally does not register in the track.  The bear has small eyes and its ears are round and erect.  The coat color of the Florida black bear is consistently black, but the summer molt of guard (outer) hair may cause a brownish appearance.  Twenty-five to 33% of individuals possess a white chest blaze.

 

 

Adult (3 years or older) male bears weigh 114 - 160 kgs. and adult females weigh 60-82 kgs.  However, with the region’s long growing season and the availability of garbage and other calorie-rich foods available to individuals foraging in human communities, bears can grow even larger.  The largest bears on record in Florida are a 624-lb male killed on a county road in southwest Florida and a 400-lb female killed on a road in northwest Florida.

 

Distribution

 
caption Figure 3. An unrooted phylogenetic tree depicting the genetic relationships among Florida black bear populations. Branch lengths correspond to genetic distance. Subpopulations are Eglin (EG), Apalachicola (AP), Aucilla (AU), Osceola (OS), Ocala (OC), St Johns (SJ), Chassahowitzka (CH), Highlands/Glades (HG), and Big Cypress (BC). Although Aucilla was treated as a separate population during genetic analysis, it is considered a part of the Apalachicola population (from Dixon et al. 2007).

Historically, the Florida subspecies inhabited all of Florida (except the lower keys) and southern Alabama and Georgia [2]. After more than 200 years of deforestation and persecution by settlers, the Florida black bear had reached a low point in numbers and distribution by 1950--1970. The subsequent regrowth of forests and reduction in wild fires which resulted in a denser shrub layer have restored much bear habitat.

 

Consequently, bear numbers have been stable to increasing, but populations remain significantly smaller than pre-Columbian estimates and the subspecies once contiguous range has been markedly fragmented.  A small subpopulation survives in southwestern Alabama (near Mobile) and another in southeastern Georgia (in and around the Okefenokee Swamp).  Approximately 80% of the Florida subspecies of black bears are found within the state of Florida in six large remnant populations (at Eglin Air Force Base, Apalachicola National Forest, Osceola National Forest, Ocala National Forest, St. Johns and Big Cypress National Preserve) and three smaller ones (at Chassahowitzka and Glades/Highlands).  Bears on the east end of the Apalachicola population, east of the Aucilla River are sometimes referred to in this article and by managers as the Aucilla population

 

Reproduction

Female bears become sexually mature at 3-4 years of age [3].  Breeding occurs from mid-June through mid-August, [4] and copulation stimulates the female to ovulate [5].  Black bear reproduction involves delayed implantation of the fertilized eggs which temporarily cease development after a few divisions, float free in the uterus, and do not implant until late November or December.  This adaptation allows bears to synchronize reproduction with annual food cycles.  Reduced food availability caused by poor acorn or berry production can result in delayed first breeding, smaller litter sizes, or reproductive failure [6] [7].  Females choose sheltered locations in dense brush, especially saw palmetto (Serenoa repens) thickets, in which to make shallow, leaf-lined depressions on the ground for dens where cubs are born.  Florida black bears build fewer dens in tree cavities than do more northern subspecies [7] [5, 8, 9, 10],  possibly due to the relative scarcity of large mature hardwoods in much of the range.  A reproductive female enters her den in mid- to late December and emerges in early to mid-April after a mean denning period of 100 - 113 days [8].  Gestation lasts 60 days, and cubs are born in late January to mid-February.  The average litter size is around two cubs [9], although greater productivity has been documented in older females and females with previous litters [10].  Newborn cubs weigh approximately 340 grams and are partially furred but are blind and toothless.  They grow fast and weigh 2.7 – 3.6 kg when they leave the den at about 10 weeks of age.  Cubs stay with their mothers and den with her the following winter.  The cubs leave their mother the following spring at 15-17 months of age prior to the female being bred [11].  Female offspring establish home ranges overlapping that of their mother’s while males typically disperse to new areas [12]. 

Population Density and Abundance

Bears are solitary, reclusive, and live in relatively low densities over large landscapes, characteristics that make a direct count of bears difficult.  However, populations can be estimated by sampling DNA from hair follicles collected from baited barbed-wire enclosures erected in bear range.  DNA analysis identifies individual bears and the pattern in which individuals are encountered in subsequent sampling has been used (analogously to mark-recapture studies) to estimate populations in Florida and southeastern Georgia (Table 1).  Populations in Chassahowitzka, and Glades/Highlands in Florida and in southwestern Alabama are too small to estimate with this method.  Anecdotal evidence from field studies in which bears were intensively trapped and radio collared suggests that Chassahowitzka has about 20 bears [13], Glades/Highlands has 150 – 200 bears, and that southwestern Alabama has 50-100 bears [14].

Table 1. Density and population abundance estimates for the Florida black bear [15].

 Population

Density (bears/km2

 Extrapolated Estimate1

 Apalachiola N.F.  0.06   438-695
 Big Cypress N.P.  0.13  516-878
 Eglin A.F.B.  0.04  63-101
 Ocala N.F.  0.24  729-1,056
 Southeast Georgia [16] [8]  0.14  600-800
 Osceola N.F.  0.14  200-313
 St Johns  0.07  96-170
 Glades-Highlands  unk  150-200
 Chassahowitzka  unk  15-20
 Southwest Alabama [17] [14]  unk  50-100
1The extrapolation of population estimates in based on the assumptions that density is constant throughout the breeding range and that optimal bear habitat is constantly available throughout. </dd>

Habitat Use and Home Range

Black bears are adaptable and thrive in a variety of forested habitats.  Where bears live is a function of nutritional needs and spatially fluctuating food sources.  The Florida black bear thrives in habitats that provide an annual supply of seasonally available foods, secluded areas for denning, and some degree of protection from humans.  Optimal habitat for the Florida black bear has been described as “a mixture of flatwoods, swamps, scrub oak ridges, bayheads, and hammock habitats, thoroughly interspersed.”[18]

Self-sustaining and secure populations of black bears are found within large contiguous forested tracts that contain understories of mast or berry-producing shrubs or trees; which are common characteristics of publicly-owned lands and commercial forests.  Imperiled populations are associated with more fragmented forests tightly bounded by urban areas and highways.

Home range size and shape is influenced by the seasonal and spatial distribution of food items, population density, reproductive status, and human-related influences such as habitat fragmentation.  Female black bears select a home range based on availability of food and cover with smaller home ranges found in better habitat.  Male black bears establish a home range in relation to the presence of females [19] [16] , and their home ranges are usually three to eight times as large as those of females [20].  The size of the home range of Florida black bears varies widely, a result of the variety of habitats and habitat quality (Table 2). 

Table 2. Annual home ranges of female Florida black bears.

Location 

 Annual Home Range km2

 Southwestern AL  [21] [9]  12.09
 Ocala NF, FL [22] [17]  20.49
 Chassahowitzka, FL [23] [13]  24.99
 Osceola NF, FL [24] [8]  30.30
 Southeastern GA [25] [8]  55.89
 Big Cypress National Preserve, FL [26] [18]  57.08
 Eglin Air Force Base, FL [27] [19]  87.49

Florida black bear females with cubs have smaller summer home ranges than females without cubs but much larger fall home ranges than females without cubs [28].  The larger fall home range of females with cubs is a response to the greater nutritional needs of rapidly growing cubs.  Related females establish annual and seasonal home ranges closer to each other than do unrelated females, and females with overlapping home ranges are more closely related than females without overlapping home ranges [29].

Black bears in natural habitats are most active at dawn and dusk but they occasionally travel extensively during the day, especially during fall, when they consume prodigious quantities of food.  Bears that live in the urban-wildland interface tend to be more active at night.  Dispersing males and bears seeking food or mates may travel extensively.  A radio-collared 2 year-old male bear was documented moving a minimum of 288 kilometers in Florida [30], and bears of both sexes enlarge their home ranges and travel more when periods of extended severe weather, such as drought, limit the availability of food.

Food Habits

Although members of the Order Carnivora, black bears evolved as omnivores at latitudes and under climate regimes characterized by dramatic fluctuations in seasonal availability of food.  Therefore, even bears in Florida exhibit an annual cycle of feasting and fasting.  In the fall, bears wander widely and forage extensively in order to accumulate enough energy in the form of fat to survive the winter.  Adult bears may increase their body weight 25-40% in the fall.  In winter bears eat much less, and reproductive females may spend many weeks in the natal den with little or no nutrition other than stored fat.  Bears are opportunistic foragers; taking advantage of seasonally abundant or available fleshy fruits, nuts (especially acorns), insects, and increasingly, foods they find near human habitation such as garbage and livestock feed.  Given the nonspecific food habits of the Florida black bear and the diversity of plant communities in its range, the list of food items is long.  However, approximately 80% of natural bear foods are plant material.  The fruits and fiber of saw palmetto are important throughout the range [31].  Beetles and colonial insects represent the largest portion of animal material consumed [32]

Mortality

Aside from conspecifics, Florida black bears have few natural predators.  Adult males opportunistically kill cubs and occasionally also kill and eat denning adult females.  Mortality is greatest in the first year of life when it can exceed 60% [33].  Survival of adult bears in unhunted populations is high. Annual female survivorship typically exceeds 90% [34] [8, 24], while that of males is 70 – 80%.  Males have lower survival rates because they have larger home ranges which exposes them to increased risks especially collisions with vehicles. The oldest wild bear documented in Florida was a 24 year-old female from the Apalachicola population.

Most documented mortality of adult Florida black bears is caused by humans (i.e., collisions with vehicles, illegal killing).  The population of bears in southeastern Georgia is the only population of Florida black bears that may be hunted legally.  In the past 10 years, the annual legal harvest in southeastern Georgia ranged from 50 to 137 bears, with an average of 71 bears, or about 10% of the estimated population.  In a highly fragmented habitat, bears have more frequent interactions with humans and human-related sources of mortality can be significant.  Adult female bears living in an urban-wildland interface outside Ocala National Forest suffered human-caused mortality at a rate that would not have been sustainable were it not for the large population of bears in the forest that served to replenish bear numbers [35].  A similar rate would be catastrophic to smaller, isolated populations such as those in Chassahowitzka and Glades-Highlands, Florida, or southwestern Alabama.

 In 2002, collisions with vehicles resulted in an annual mortality rate of 4.8% of the Florida bear population.  Nevertheless, populations with reproductive characteristics common to most populations of the Florida black bear (females first reproduce at 3.0 years and produce 2 cubs every two years) can sustain an annual mortality as great as 23% [36].  Many bears survive collisions with vehicles but sustain significant injuries.  Twelve of 92 (13%) juvenile and adult bears captured in Ocala National Forest had one or more healed skeletal injuries, primarily limb fractures that that probably resulted from vehicular collisions [37].

Illegal killing of bears is a regular though relatively unimportant cause of death.  Most studies involving radio-collared bears in Florida have found the incidence of illegally killed bears is rare within large contiguous land parcels but substantially more common within the fragmented habitats near urban areas.

 

caption Figure 3. An unrooted phylogenetic tree depicting the genetic relationships among Florida black bear populations. Branch lengths correspond to genetic distance. Subpopulations are Eglin (EG), Apalachicola (AP), Aucilla (AU), Osceola (OS), Ocala (OC), St Johns (SJ), Chassahowitzka (CH), Highlands/Glades (HG), and Big Cypress (BC). Although Aucilla was treated as a separate population during genetic analysis, it is considered a part of the Apalachicola population (from Dixon et al. 2007).

 

Disease is uncommon in black bears.  There have been no reports of rabid black bears in Florida and only a few from elsewhere.  Demodetic mange resulting in generalized hair loss in adult females, is relatively common (78%) in one locale on the western border of Ocala National Forest.  Few cases have been observed in any other Florida population although other cases have been reported in other states [38].  Demodetic mange is transmitted from females to their offspring but males recover by their second year.

Genetic Profile

Bears are particularly vulnerable to habitat loss and fragmentation because of their low numbers, low densities, large home ranges, low productivity, and higher mortality rates when living in fragmented habitat.  Habitat fragmentation and degradation have reduced what was once a single large population of bears  into smaller, more isolated populations.  Isolation of populations and reduction of population size may cause a decrease in genetic variation, which may reduce the ability to adapt to changes in the environment, cause inbreeding depression, and increase the probability of extinction

An analysis of the genetic structure of the Florida black bear indicated that many populations have been isolated from one another long enough and completely enough that measurable genetic differentiation has occurred.  This is most evident in the Chassahowitzka, Glades/Highlands, and Eglin populations (Figure 3).  Because the degree of genetic differentiation exceeded that which could be explained by distance alone, extensive habitat fragmentation must also be a factor.  Additionally, the level of genetic variation within the Chassahowitzka and Glades/Highlands populations is among the lowest reported for any bear population anywhere.  The small population of bears in southwestern Alabama also has low genetic variation and is highly inbred [39]

Ecological Significance of Bears

Black bears are recognized as an umbrella species, i.e. one whose habitat requirements overlap those of many other species.  Conservation measures that protect black bears, therefore, also protect those other species.  Benefits to bears are sometimes cited as justification for land conservation in Florida.  Given the large habitat requirements of bears and the diversity of habitats they use, many species have benefitted from the umbrella of bear conservation. 

Further Reading

  1. ^Hall, E. R., and K. R. Kelson.  1959.  The mammals of North America.  The Ronald Press, New York.
  2. ^^Harlow, R. F.  1961.  Characteristics and status of Florida black bear.  Transactions of the North American Wildlife Conference.  26:481-495.
  3. ^Hall, E. R.  1981.  The mammals of North America.  2nd ed., vol. 2.  John Wiley and Sons, New York. 
  4. ^Pelton, M. R. and F. T. van Manen.  1997.  Status of black bears in the southeastern United States. Pp. 31-44 in A. L. Gaski and D. F. Williamson, eds. Proceedings of the Second International Symposium in the Trade of Bear Parts. Traffic USA/World Wildlife Fund, Washington, D.C.
  5. ^^^^Garrison, E. P., J. W. McCown, and M. K. Oli.  2007.  Reproductive ecology and cub survival of Florida black bears.  Journal of Wildlife Management 71:720-727, http://www.wec.ufl.edu/faculty/olim/publications.html .
  6. ^^^Garrison, E. P.  2004.  Reproductive ecology, cub survival, and denning ecology of the Florida black bear.  Thesis, University of Florida, Gainesville, Florida.
  7.  ^^^^^^Pelton, M. R.  1982.  Black bear.  Pp 504-514 in J.A. Chapman and G.A. Feldhamer,  eds., Wild mammals of North America.  The Johns Hopkins University Press, Baltimore, Maryland.
  8. ^^^^^Dobey, S., D. V. Masters, B. K. Scheick, J. D. Clark, M. R. Pelton, and M. E. Sunquist.  2005.  Ecology of Florida black bears in the Okefenokee-Osceola Ecosystem.  Wildlife Monographs 158. http://research.myfwc.com/publications/publication_info.asp?id=49110 .
  9. ^^^Edwards, A. S. 2002.  Ecology of the black bear (Ursus americanus floridanus) in southwestern Alabama. Thesis, University of Tennessee, Knoxville, Tennessee.
  10. ^Hersey, K. R., A. S. Edwards, and J. D. Clark.  2005.  Assessing American black bear habitat in the Mobile-Tensaw Delta of southwestern Alabama.  Ursus 16:245-254.
  11. ^Siebert, S. G., J. C. Roof, and D. S. Maehr.  1997.  Family dissolution in the Florida black bear.  Florida Field Naturalist 25:103-104.
  12. ^^Moyer, M. A., J. W. McCown, and M. K. Oli.  2006.  Does genetic relatedness influence space use pattern?  A test on Florida black bears.  Journal of Mammalogy 87:255-261 http://www.wec.ufl.edu/faculty/olim/publications.html .
  13. ^^Orlando, M. A.  2003.  The ecology and behavior of an isolated black bear population in west central Florida.  Thesis, University of Kentucky, Lexington, Kentucky.
  14. ^^Hristienko, H., and J. E. McDonald Jr.  2007.  Going into the 21st century: a perspective on trends and controversies in the management of the American black bear.  Ursus 18: 72-88.
  15. ^Simek, S. L., S. A. Jonker, B. K. Scheick, M. J. Endries, and T. H. Eason.  2005.  Statewide assessment of road impacts on bears in six study areas in Florida from May 2001 to September 2003.  Final Report Contract BC-972.  Florida Department of Transportation, Tallahassee, Florida. http://myfwc.com/WildlifeHabitats/Bear_reports.htm
  16. ^Sandell, M.  1989.  The mating techniques of solitary carnivores.  Pp. 164-182 in J. Gittleman, ed., Carnivore behavior, ecology, and evolution.  Cornell University Press, Ithaca, New York.
  17. ^McCown, J. W., P. Kubilis, T. H. Eason, and B. K. Scheick.  2004.  Black bear movements and habitat use relative to roads in Ocala National Forest.  Florida Fish and Wildlife Conservation Commission.  Final Report Contract BD-016 for Florida Department of Transportation. http://myfwc.com/WildlifeHabitats/Bear_reports.htm
  18. ^Land, E. D., D. S. Maehr, J. C. Roof, and J. W. McCown.  1994.  Southwest Florida black bear distribution, movements, and conservation strategy.  Florida Game and Fresh Water Fish Commission.  Tallahassee. 
  19. ^Stratman, M. R.  1998.  Habitat use and effects of fire on black bears in northwest Florida.  Thesis, University of Tennessee, Knoxville, Tennessee.
  20. ^Moyer, M. A., J. W. McCown, and M. K. Oli.  2007.  Factors influencing home-range size of female Florida black bears.  Journal of Mammalogy 88:468-476.
  21. ^Maehr, D. S., J. N. Layne, E. D. Land, J. W. McCown and J. C. Roof.  1988.  Long distance movements of a Florida black bear.  Florida Field Naturalist 16:1-6.22. Maehr, D. S., T. S. Hoctor, L. J. Quinn, and J. S. Smith.  2001.  Black bear habitat management guidelines for Florida.  Technical Report No. 17.  Florida Fish and Wildlife Conservation Commission, Tallahassee. http://myfwc.com/WildlifeHabitats/Bear_reports.htm23. Maehr, D. S. and J. R. Brady.  1984.  Food habits of Florida black bears.  Journal of Wildlife Management 48:230-235.
  22. ^Hostetler, J. A., J. W. McCown, E. P. Garrison, A. M. Neils, M. E. Sunquist, S. L. Simek, and M. K. Oli. 2009. Demographic consequences of habitat fragmentation: Florida black bears in north central Florida. Biological Conservation 142:2456-2463. http://www.wec.ufl.edu/faculty/olim/publications.html
  23. ^McCown, J. W., P. Kubilis, T. H. Eason and B. K. Scheick.  2009.  Effect of traffic volume on American black bears in central Florida, USA.  Ursus 20:39-46. http://research.myfwc.com/publications/publication_info.asp?id=58664
  24. ^Bunnell, F. G. and D. E. N. Tait.  1980.  Bears in models and reality-; implications to management.  International Conference on Bear Research and Management 4: 15-24.
  25. ^McCown, J. W., P. Kubilis, T. H. Eason, and B. K. Scheick.  2004.  Black bear movements and habitat use relative to roads in Ocala National Forest.  Florida Fish and Wildlife Conservation Commission.  Final Report Contract BD-016 for Florida Department of Transportation. http://myfwc.com/WildlifeHabitats/Bear_reports.htm
  26. ^Foster, G. W., T. A. Cames, and D. J. Forrester.  1998.  Geographical distribution of Demodex ursi in black bears from Florida.  Journal of Wildlife Diseases 34: 161-164.
  27. ^Cunningham, M. W., S. Terrell, B. Ferree, and L. M. Penfold.  2007.  Epizootiology of generalized demodicosis in a Florida black bear population.  Proceedings of 56th Annual Wildlife Disease Association Conference.  Estes Park, Colorado.
  28. ^Dixon, J. D., M. K. Oli, M. C. Wooten, T. H. Eason, J. W. McCown, and M. W. Cunningham.  2007.  Genetic consequences of habitat fragmentation and loss: the case of the Florida black bear (Ursus americanus floridanus).  Conservation Genetics 8: 455-464. http://www.wec.ufl.edu/faculty/olim/publications.html .
Glossary

Citation

McCown, W. (2013). Florida Black Bear. Retrieved from http://www.eoearth.org/view/article/51cbedcc7896bb431f693fcb

2 Comments

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Catherine Najera wrote: 08-14-2012 08:26:21

Mr. McCown, I tried to private message you about a very large bear I observed for the past two nights. Did you get my message? If so, could you get in contact with me? I am not familiar with this site. I joined so I could get in touch with you. Thank you.

Robert Funderburk wrote: 12-11-2011 11:32:17

Mr McCown, my name is Robert Funderburk, a student at Western Carolina University, and I am doing analysis of black bear nuisance reports for Northwest Florida over the past 10 years. Is it possible for your Eglin population, ~83 individuals in 2010, to generate 536 nuisance incidence for that same year?