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KEYWORDS: American black bear, elasticity, life table response experiments, North Carolina, population growth rate, Population modeling, sensitivity, southern Appalachians, Ursus americanus, vital rates
Analyses of large, long-lived animals suggest that adult survival generally has the potential to contribute more than reproduction to population growth rate (λ), but because survival varies little, high variability in reproduction can have a greater influence. This pattern has been documented for several species of large mammals, but few studies have evaluated such contributions of vital rates to λ for American black bears (Ursus americanus). We used variance-based perturbation analyses (life table response experiments, LTRE) and analytical sensitivity and elasticity analyses to examine the actual and potential contributions of variation of vital rates to variation in growth rate (λ) of a population of black bears inhabiting the Pisgah Bear Sanctuary in the southern Appalachian Mountains of North Carolina, using a 22-year dataset. We found that recruitment varied more than other vital rates; LTRE analyses conducted over several time intervals thus indicated that recruitment generally contributed at least as much as juvenile and adult survival to observed variation in λ, even though the latter 2 vital rates had the greater potential to affect λ. Our findings are consistent with predictions from studies on polar bears (U. maritimus) and grizzly bears (U. arctos), but contrast with the few existing studies on black bears in ways that suggest levels of protection from human-caused mortality might explain whether adult survival or recruitment contribute most to variation in λ for this species. We hypothesize that λ is most strongly influenced by recruitment in protected populations where adult survival is relatively high and constant, whereas adult survival will most influence λ for unprotected populations.
We asked whether den site characteristics of Scandinavian brown bears (Ursus arctos) were related to bear sex or age by analyzing the nearest distances to human structures within 10 km, the forest composition within 50 m, and topography within 5 m of 391 winter dens used by 114 individuals during 1986–2003 in south-central Sweden. Subadult males and subadult females used more pine (Pinus sylvestris) than spruce (Picea abies) denning habitats than did adult males. Adult males selected nest dens over rock dens more strongly than did subadult males, and they selected nest dens over anthill, soil, and rock dens more strongly than did subadult females, pregnant females, or females with cubs. Topography differed among den types but showed a poor relationship with different age–sex classes of bears. Abandoned dens were located closer to plowed roads than dens used successfully all winter. Adult males denned farther from permanently occupied houses and plowed roads than did other categories of bears, perhaps because they were least tolerant of human disturbance. In general, den sites of adult males differed the most from other age–sex classes of bears.
The management of human–American black bear (Ursus americanus) conflict has been of significant concern for Yosemite National Park (YNP) personnel since the 1920s. Park managers implemented the YNP Human–Bear Management Plan in 1975 in an effort to reduce human–bear conflicts, especially in the extensively developed Yosemite Valley (YV). We used scat analysis to estimate annual and seasonal food habits of black bears in YV during 2001–02. We assessed the success of efforts to reduce the availability of anthropogenic foods, including garbage, by examining changes in the diet compared to a study from 1974–78 (Graber 1981). We also quantified consumption of non-native fruit to address its possible contribution to human–bear conflicts. The annual percent volume of human-provided food and garbage in black bear scats in YV decreased from 21% to 6% between 1978 and 2002, indicating YNP efforts have been effective. We found high use of non-native apples by bears throughout YV. Non-native food sources could be contributing to habituation and food conditioning, given their proximity to developed areas of YV. We recommend that YNP managers continue to (1) adapt and improve their management tools to address changing circumstances, (2) quantify the success of new management tools, and (3) reduce the availability of non-native food sources.
The Andean (spectacled) bear (Tremarctos ornatus) is the only extant species of bear in South America. This species is considered Vulnerable by the International Union for Conservation of Nature (IUCN), although current population sizes are unclear. To study Andean bears using DNA and non-invasive sampling, we screened 13 microsatellite loci using DNA extracted from blood, saliva, hair, and feces from 16 captive bears. Polymorphic loci were tested with samples from wild bears using DNA extracted from hair and feces collected in the Oyacachi territory inside the Cayambe-Coca Reserve in Ecuador during 2000 and 2001. Ten loci produced reliable results and were polymorphic with a mean of 4 alleles/locus. A minimum of 7 loci were needed for individual identification of wild bears using a probability of identity for siblings PID(sib) threshold of <0.01. Andean bears in the Oyacachi territory had moderate levels of genetic diversity (expected heterozygosity, HE = 0.45). Although genotyping success rates were low in this pilot study, noninvasive genetic sampling of Andean bear hair and feces provides a useful alternative method for studying this species. When launching a project to census wild animals using hair or fecal samples, we recommend re-evaluating at least the 9 most informative microsatellite loci (G10M, UarMu50, G10H, G10B, G10J, G10X, G10P, G10O, and CXX20), recalculating probability of identity (PID) values and considering genotyping error rates.
We propose a new cover cylinder as a useful tool for a single observer to measure horizontal cover in the field. We compared it with 4 other methods for measuring horizontal cover at brown bear (Ursus arctos) beds, with all measurements taken 10 m from beds in the 4 cardinal directions. We also compared cylinder cover values from a fixed distance with an index of cover, namely a sighting distance, D, the minimum distance at which the cylinder could no longer be seen; we also compared measurements from a random direction and from the 4 cardinal directions. The cylinder provided measurements comparable to other devices, including a cardboard profile of a bedded bear, and was the most practical to use in the field. Measuring D was scarcely more time consuming than measuring cover from the fixed 10-m distance, and D is better for statistical analysis. We recommend the cylinder, and using the index of cover, D, taken from the 4 cardinal directions, when assessing horizontal cover for bears or other medium and large terrestrial vertebrates.
Field workers handling bears continually strive to improve their field methods and reduce risks to animals during capture. Zolazepam–tiletamine (ZT) is the standard anesthesia currently used in bear captures, but has a prolonged recovery because there is no antagonist. Researchers are increasingly using xylazine, zolazepam, and tiletamine (XZT) in combination as an improvement to ZT alone. Because xylazine provides excellent analgesic qualities and can be antagonized, XZT has the potential for effective anesthesia and faster recovery time for bears. I assessed recovery times and considered physiological parameters to asses the quality of anesthesia of grizzly (Ursus arctos) and American black (U. americanus) bears anesthetized with XZT, for which the xylazine portion was antagonized by yohimbine (XZT/Y). I compared these recovery times with unpublished recovery time data on bears anesthetized with ZT only. My XZT/Y samples came from research projects in western Montana, northern Idaho, and southeast British Columbia; bears anesthetized with ZT only came from Alberta, Canada, and the Greater Yellowstone Project of Montana, Wyoming, and Idaho, USA. Bears administered the XZT/Y protocol recovered from anesthesia 1.61 (95% CI = 1.28–2.01) times faster than bears anesthetized with ZT combinations. Bears administered XZT/Y at dosage rates presented here received adequate anesthesia for humane handling as indicated by the physiological parameters monitored.
We investigated the potential use of leptin as a wildlife management tool to monitor adiposity in American black bears (Ursus americanus). Body mass (BM), body condition index (BCI), serum leptin concentration, and percent of body fat were measured in semi-free ranging (SFR) adult male (South Dakota, Oct 2003–Jun 2004) and free-ranging (FR) adult females (Colorado and Wyoming, 1997–99) in fall, winter, spring, and summer. These variables were analyzed by simple and multiple linear regression models to determine their relative value as predictors of body fat proportion over a wide range of adiposity (7.5–48% of total BM). Log-transformed serum leptin concentration (ln leptin) was the most consistent single surrogate predictor of percent body fat when compared with BM and BCI. For both SFR and FR cohorts, ln leptin was strongly predictive of percent body fat within the range of adiposity between 7.5–35%. Moreover, the best predictors of body fat were multiple regression models that included ln leptin in both SFR males (AICc = 75.97, ω = 0.61) and FR females (AICc = 85.07, ω = 0.54). Therefore, serum leptin markedly improves the resolution and accuracy of common field estimates of body condition in black bears. Because it is strongly associated with and predictive of bioelectrical impedance assay (BIA) estimation of body fat, further investigation of serum leptin as a predictor of adiposity is warranted.
American black bear (Ursus americanus) hunting has come under close scrutiny over the past decade. As black bear populations have increased and expanded, wildlife agencies have been faced with new challenges on how to set population and harvest goals. Wildlife agencies have altered proposed regulations or have had seasons entirely stopped because of public opposition, necessitating a proactive approach to wildlife management based on a scientific understanding of public opinion rather than reactive decision-making in response to public resistance. In November–December 2006, we conducted a telephone survey of 1,206 West Virginia residents to determine their opinions and attitudes toward black bear populations and hunting seasons and to help strengthen the state's black bear management strategies. Although the majority of West Virginians, nearly 3 of 4 respondents in this study, indicated they know at least something about black bears in West Virginia, there were significant regional differences in the public's assessment of their knowledge of the species. Although most respondents thought the black bear population size was “about right,” again, there were regional differences among respondents. In general, most respondents supported black bear hunting if the population was carefully monitored, if they knew the population was stable, or both; however, a number of regional and sociodemographic characteristics appeared to influence public opinion on black bear hunting and hunting seasons in the state, and support for specific seasons varied considerably according to hunting method. Interestingly, our study found that even among hunters, public opposition exceeded support for the current, year-round training season of black bear hunting dogs without harvesting animals in the state. Although it is important for wildlife managers to consider human dimensions and public opinion data in conjunction with biological data when making management decisions, we demonstrate that it also is important for managers to consider regional and sociodemographic differences with respect to attitudes and opinions when making management decisions and population objectives.
All bears give birth to highly altricial young, but maternal style is markedly divergent among species. Like many aspects of sun bear (Helarctos malayanus) life history, maternal care in this species is poorly documented. Using detailed systematic behavioral observations, we provide the first quantitative report on the mother–cub relationship and early behavioral development in a sun bear. We summarize temporal changes in mother–cub behavior as the cub ages and evaluate maternal investment in the cub. We also provide developmental milestones documented in 2 cubs born (one in 2004, one in 2006) at the San Diego Zoo and compare them with those available in the literature. This sun bear mother displayed behavior indicating a high level of behavioral investment in young offspring while still in the den. She held the cub off the ground, cradled it to reduce the cub's exposure to ambient air, and was attentive to the cub's needs, responding to nearly 50% of the cub's vocalizations and grooming the cub frequently. We conclude that the maternal care behavior of sun bears appears to be active, comparable to the giant panda (Ailuropoda melanoleuca) and different from the more passive maternal care displayed by American black (Ursus americanus) and brown bears (U. arctos) during the denning phase. A growing number of studies of maternal care in ursids are beginning to provide insights into comparative life histories.