Wednesday, June 8, 2011

American Black Bear Habitat In Natural Trap Caves

Remains of 22 American black bears (Ursus americanus) were excavated from 2 natural trap caves in Missouri during the late 1950s. Age, sex, and size characteristics based on analysis of ursid teeth from the caves corroborates wildlife studies that suggest that subadult to young-adult male bears are relatively vulnerable to accidental deaths in their search for food compared to members of other age sex cohorts. This information is of interest to wildlife biologists given that North American Black bears and humans increasingly share habitat. Data on native Missouri black bears are also of general interest because little is known about this population, which was extirpated by the beginning of the twentieth century, and because a
reintroduced population is expanding in the southern portion of the state.

American Black Bear

Two natural trap caves excavated by paleozoologists in the 1950s in Missouri produced historicperiod (post AD 1541 [O’Brien and Wood 1998) assemblages of animal remains that are dominated by American black bear (Ursus americanus). The bones of 10 bears (based on frequency of femora) were recovered from Lawson Cave, a vertical shaft cave in central Missouri (Wells 1959). The deposit was completely excavated and screened through 0.4 cm (J-inch) mesh; all excavated osteological materials were kept for analysis. The cave is a bottle-shaped trap, 11.5 meters deep with a 1.78 x 0.79 meter entrance. A collapsed horizontal entrance abuts the vertical shaft, but it is 4.5 meters above the inverted walls of the trap; thus, it never served as an exit from the trap chamber. American Black bear remains from the cave have been radiocarbon dated to the historic period (Wolverton and Lyman 1998, Wolverton 2001).

The taxa represented in faunas from both caves tend to be those occurring today in deciduous forest habitat. Both caves were natural traps to which bears were attracted by carrion. American Black Bears and members of other species were trapped in and subsequently perished within the caves. In both assemblages, remains of mammals other than bears are common including other carnivores, rodents, and lagomorphs. .Remains of domestic pig at Lawson Cave and turkey vulture at Jerry Long Cave are relatively abundant, and both species are carrion scavengers.

This aricle examines the age, sex, and size distributions of the black bears recovered from Lawson and Jerry Long caves through morphometric and mortality analysis of teeth. The ursid remains from these caves are potentially of interest to wildlife biologists. American Black bears are uncommon in Missouri and other parts of the agricultural Midwest because they were extirpated after Euro-American occupation; however, they have been successfully reintroduced into the Ozark highlands in Missouri and Arkansas (Schwartz and Schwartz 2001, Smith and Clark 1994). American Black Bear remains from these caves represent individuals from before extirpation, a population about which little is known. In addition, the ursid remains from both caves are dominated by youngadult males, which relates to age- and sex-specific life history characteristics that are relevant in modern wildlife management of bears.

American Black Bear

Although a host of variables are recommended for aging American black bears (Marks and Erickson 1966), not all of these are amenable for use with paleozoological specimens, such as those from Lawson Cave and
Jerry Long Cave, which are commonly disarticulated from crania and mandibles or fragmentary. Further,
tooth wear aging is less destructive than use of cementum annuli to age canine teeth. However, because wear rates vary by individual, the age classes used here were considered ordinal scale and assessed non-parametrically following the assumption that older individuals tend to contain relatively worn
permanent teeth.

The modern Midwest sample, especially bears from Arkansas, primarily represented individuals reintroduced
to northern Arkansas from Minnesota (Smith and Clark 1994), which are expected to be large in body size. That this modern sample reflected size of relatively large bears is important for 2 reasons. First, that size of the natural trap individuals compares with that of males in the Midwest sample supports the interpretation that the former sample indeed represented males because the natural trap individuals are large. Second, pre-extirpation Missouri American black bears appear to have been relatively large in size, which is of interest because very little is known concerning the original Midwest population (Wolverton and Lyman 1998).

American black bear, Missouri, natural traps, paleozoology, subadult male mortality, Ursus americanus


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