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Information regarding American black bear (Ursus americanus) mortality caused by disease is limited. Pneumonia is a common respiratory disease that affects many species of wildlife and can result in death. In February 2011, we investigated the death of a yearling male black bear and determined cause of death to be aspiration pneumonia. We found sections of lung were diffusely congested and edematous. A bacterial culture of lung tissue revealed numerous colonies of Klebsiella spp., Alcaligenes faecalis, Aeromonas spp., Corynebacterium spp., and Streptococcus spp. The mixed bacterial colonization of the lungs associated with minimal inflammation is consistent with terminal aspiration of gastrointestinal contents resulting in aspiration pneumonia. Documentation of aspiration pneumonia in black bears can be useful for future researchers interested in the effects of disease on bears.
Winter denning is a critical component of American black bear (Ursus americanus) ecology. Mississippi has a small recolonizing population (about 50 individuals), including the federally-threatened Louisiana black bear (U. a. luteolus), and knowledge of den use is needed to effectively conserve the species. We quantified black bear denning chronology (n = 15) and den use (n = 18) in Mississippi during 2005–2011. Denning was highly variable and females entered dens earlier than males and emerged later; multiple den use by both sexes in a single winter was common. We recorded equal numbers of tree and ground dens, with ground dens at higher elevations surrounded by dense vegetation. With the exception of all bears denning each winter, black bears in Mississippi exhibited denning chronology and characteristics similar to other black bear populations in the southeastern United States.
We examined body condition and growth dynamics of wild American black bears (Ursus americanus) inhabiting interior regions of northern Canada, 1998–2009. Differences in body condition were unrelated to gender, but we found significant effects of age and season as well as an interaction between the two. We found a trend toward improved body condition in older bears that increased during summer and peaked in fall, with lowest values observed in spring. The von Bertalanffy growth function showed that males reached asymptotic body length 9.3% longer, and mass 29.3% heavier, than females. Our growth models indicated an association between sexual growth divergence and the onset of reproduction in females, together with more rapid and prolonged male growth. We suggest that sexual size dimorphism develops in part from constraints on female growth from high energetic costs of reproduction. In contrast, males experience no comparable energetic trade-off after reaching sexual maturity and apparently allocate available energetic resources to growth of larger body size, which benefits more competitive males in terms of increased reproductive success.
Brown bears (Ursus arctos) are a long-lived and widely distributed species that occupy diverse habitats, suggesting ecological flexibility. Although inferred for numerous species, ecological flexibility has rarely been empirically tested against biological outcomes from varying resource use. Ecological flexibility assumes species adaptability and long-term persistence across a wide range of environmental conditions. We investigated variation in population-level, coarse-scale resource use metrics (i.e., habitat, space, and food abundance) in relation to indices of fitness (i.e., reproduction and recruitment) for brown bears on Kodiak Island, Alaska, 1982–97. We captured and radiocollared 143 females in 4 spatially-distinct segments of this geographically-closed population, and obtained ≥30 relocations/individual to estimate multi-annual home range and habitat use. We suggest that space use, as indexed using 95% fixed kernel home ranges, varied among study areas in response to the disparate distribution and abundance of food resources. Similarly, habitat use differed among study areas, likely a consequence of site-specific habitat and food (e.g. berries) availability. Mean annual abundance and biomass of spawning salmon (Oncorhynchus spp.) varied >15-fold among study areas. Although bear use of habitat and space varied considerably, as did availability of dominant foods, measures of fitness were similar (range of mean litter sizes = 2.3–2.5; range of mean number of young weaned = 2.0–2.4) across study areas and a broad range of resource conditions. Our data support the thesis that brown bears on Kodiak Island display ecological flexibility. This adaptability is likely representative of the entire species and has helped facilitate its wide geographic distribution and abundance. We suggest variation in brown bear resource use necessitates area-specific management strategies to ensure suitable conditions for their long-term persistence.
Harvest data provide readily available and relatively inexpensive information about populations of game species. However, these data are not necessarily representative of standing populations and may have limited applicability in management. We applied a method of harvest data analysis based on the changing sex ratio of the harvest with age to American black bear (Ursus americanus) harvest data from 1985–2005 in Montana. We assessed the ability of this method to identify assumption violations and the extent of resulting bias. A change in the relative vulnerability of females at primiparity due to protection of mothers with cubs from harvest was observable as a drop in the proportion of females in the harvest at the age of maturity. A changing harvest rate produced changing harvest rate estimates, but the estimates lagged up to 10 years behind the actual rate. Other assumption violations, such as unequal non-harvest mortality between sexes and stochasticity in the harvest rate, are not apparent in the harvest data themselves. If total harvest is known and the harvest rate is estimable, it may be possible to use harvest to identify population declines. However, we found with simulations that, in many cases, 10–15 years of harvest data are needed to identify a statistically significant decline. If all assumptions are met, we estimated harvest rates in Montana as 4.6% for females and 10.4% for males; these are overestimates if males have higher non-harvest mortality than females. Montana's harvest data did not show an apparent decline in the relative vulnerability of females at maturity, despite nominal protection of mothers accompanied by cubs. Analyses of harvest data also contradicted the hypothesis, based on meta-analysis of demographic data, that black bears were declining in Montana.
Capture–mark–recapture (CMR) population parameter estimation utilizing DNA analysis from remotely-collected hair samples to identify individuals and generate encounter histories has become the standard methodology for estimating abundance of American black (Ursus americanus) and grizzly bear (U. arctos) populations. However, few published studies have examined the time frame for efficiently collecting high-quality hair samples. Our objectives were to examine several measures of hair trapping success and sample quality, such as DNA amplification rates and the mean number of black bear hair samples collected per trap visit, from hair-snare samples collected in 2 non-overlapping, multi-interval sampling frames conducted during 2005 and 2006 at Fort Drum Military Installation in northern New York. Through our data analyses and a review of 12 other bear CMR studies using remote hair sampling, we emphasize that temporal sampling frame is a crucial consideration in study design. To avoid biased population estimates and to use financial, personnel, and temporal resources effectively, hair sampling should be conducted during late spring and early summer.
Ants are an important food resource for most of bear species. During the summer, Japanese black bears (Ursus thibetanus japonicus) use grasslands in the ∼60 km2 Ashio area as an ant feeding site. We studied levels of myrmecophagy using GPS locations and activity sensor information along with direct observations of 2 bears during 2004 and 2005. We measured species composition, biomass, and nutrient contents of the ants and estimated use of ants through bear scat analysis. Both the number of ant species and biomass were higher in Ashio than in the adjacent forest areas. We recorded 15 ant species, 9 of which were fed on by the bears. Lasius flavus and L. hayashi were most abundant species and the species used by bears most often. Bears spent 7–8 hours/day feeding on ants. We estimated that they potentially ate 50,000–60,000 mg (dry weight)/day of ants, whose energy content was around 180–300 kcal/d, insufficient to meet their basal and field metabolic needs. Bears may have used ants for essential amino acids that they are unable to produce themselves. Assuming bears come to Ashio specifically for ants, these grasslands are valuable for bears at a time when vegetative food resources are limited.
Defining areas of potential distribution for large carnivores is a critical step for generating conservation strategies. Ecological niche modelling is an important tool for identifying potential areas for conservation of carnivores, such as American black bears (Ursus americanus) in the Sierra Madre Occidental (SMOcc) and the Sky Islands (SI) region of Northwest Mexico. Our objective was to define areas and environmental factors that influence bear distribution and understand the causes of their absence. We used GARP (genetic algorithm for rule-set prediction) to define the potential area of distribution using historical and current records of black bear (n = 582) and 23 bioclimatic and physical variables. We obtained a consensus model with a high probability of occurrence and power prediction representing 80% of the SMOcc (221,078 km2), including the SI region (Sonora and Chihuahua deserts). The ecological dimensions of the model include temperate dry and mixed forest, low rainfall, low temperatures, and elevation above 1,500 m, with considerable slope variation. Information provided by residents of Aguascalientes, Chihuahua, Durango, and Zacatecas indicate that the species was extirpated in central and southwest Durango and Zacatecas about 50 years ago, coinciding with the use of 1080 poison (sodium fluoroacetate) to eradicate livestock predators, combined with habitat loss, fragmentation, and excessive hunting in the region. These factors precipitated the regional extirpation of the species. Areas such as those we have identified may be important sites for the reintroduction of black bears.
Of the threats facing sloth bear (Melursus ursinus) populations, habitat fragmentation is the most pressing. Although conservation requires protection of habitat, little is known about the factors governing sloth bear occurrence. We used camera-trapping data to investigate occupancy of sloth bears in Mudumalai Tiger Reserve, an important conservation site in India during January–April 2010. Presence–absence data, collected under a systematic sampling framework, were used to test a priori hypotheses incorporating covariates believed to influence sloth bear occurrence. The estimated occupancy of sloth bears in the study area was 0.83 (SE = 0.01) with a detection probability of 0.23 (SE = 0.07). We found that no model with covariates was as strongly supported as the null model, suggesting that covariates we chose were relatively weak predictors of use. That said, our results suggested that sloth bear use was associated with deciduous forests; weaker evidence was found for association with termite mounds and fruiting trees. In the future, monitoring programs for wide-ranging species could benefit from using occupancy surveys.
We provide the first known documentation of a fatal brown bear (Ursus arctos) poisoning with carbofuran (an acetylcholinesterase inhibitor) in Croatia. Diagnosis using liquid chromatography–mass spectrometry confirmed the presence of high concentrations of carbofuran in liver and kidney tissue (12.650 and 2.695 ppm, respectively). These measurements, combined with the very small distance between poisonous baits and the brown bear carcass, provided the basis on which we concluded that the animal consumed a lethal dose of carbofuran and succumbed to acute poisoning soon thereafter. We believe this mortality was caused by the illegal placement of this poison probably to eliminate perceived pests, such as jackals (Canis aureus) or foxes (Vulpes vulpes). Our documentation may help identify similar cases and raise awareness of the risks posed by illegal poisons for non-target species, particularly scavengers such as bears.
Harvesting wild animals can affect demographic parameters and life history traits of surviving individuals. Most brown bear (Ursus arctos) populations currently experience low levels of hunting. We characterized mortality patterns in a heavily exploited transboundary brown bear population in Slovenia, Central Europe. Overall, 927 brown bears were reported removed from 1998 to 2008. Most (97%) removals were human caused including removals from hunting (59% of removals), management removals of problem individuals (18%), and vehicle collisions (16%). Median age of bears removed in Slovenia was 2.3 years, and 78% of bears removed were <4 years old. Removal was male-biased overall (59%), mainly due to the high percent (49%) of young (<4 years old) males removed during hunting, a possible consequence of sex-related differences in bear behavior and harvest regulations. However, the effect of sex-biased removal was less than expected based on removal data, and it appears a different harvest regimen in neighboring Croatia and sex-biased dispersal of young bears buffered the demographic effects of selective harvest in Slovenia. We also observed that annual proportion of females in harvests increased with harvest intensity. More males were removed among younger classes, whereas females started to dominate above the age of 8 years. About 20% of the brown bear population was removed annually by legal harvest; this is one of the highest harvest rates reported for this species.
We evaluated the efficiency of an extension of a single season capture–mark–recapture (CMR) population estimation method, a closed-capture robust-design model, to monitor trends in population size, apparent survival, and temporary emigration rates over a 5-year period for a low-density population of American black bears (Ursus americanus) in north central Utah, USA. We also used robust-design Pradel models to estimate finite rate of population change and recruitment. We identified individual bears through genetic analysis of tissue samples collected non-invasively at scent-lured sampling sites. Although the population was relatively small ( = 15–22), the Huggins robust-design model provided precise estimates of abundance (CV = 8–14%) and female apparent survival (CV = 9%). Apparent survival for females (φ = 0.80, SE = 0.07) was 2.2× higher than for males (φ = 0.36, SE = 0.12; P = 0.003). In contrast, temporary emigration was 40.8× higher for males (γ″ = 0.58, SE = 0.24) than for females (γ″ = 0.004, SE = 0.06; P = 0.024). Data were insufficient to estimate probability of staying for either sex. From the Pradel model, finite rate of population change was similar for males and females (λ = 1.05, SE = 0.12 for females; λ = 1.11, SE = 0.16 for males), but recruitment was 3.0× higher for males (f = 0.75, SE = 0.17) than for females (f = 0.25, SE = 0.10; P = 0.013). Population size appeared to be stable or slightly increasing over the 5-year period. This noninvasive CMR study provided relatively efficient, precise estimates of a low-density black bear population on a small study site. We recommend using robust-design closed-capture models if samples are taken over multiple years; in addition to population size, apparent survival, movement, recruitment, and finite population change can be estimated, providing timely insights into population trends and the mechanisms driving them.