Using stable isotopes to assess dietary changes of American black bears from 1980 to 2001

Abstract

We measured stable carbon and nitrogen isotope ratios in 117 hair samples from American black bears (Ursus americanus) in Great Smoky Mountains National Park, Tennessee, during 1980-2001 from live-trapped bears. We also collected hair from bears with known diets to compare with the wild bears. We hypothesized that biological factors (age, mass, and sex), food availability (hard mast and wild hogs (Sus scrofa)), and nuisance status would influence food selection by black bears and changes in their feeding history would be measureable using stable isotopes. We developed a set of a priori models using nine variables to examine changes in black bear stable isotope values. We found no support for changes in δ(13)C values associated with any of the nine variables we analyzed. Bears had enriched (15)N in years with low white oak mast production and depleted (15)N when white oak mast was abundant. Subadults had enriched (15)N compared with adults and older adults. Variation in δ(15)N increased from 1980-1991 to 1992-2000 when hard mast production had greater fluctuations. Bears in a better physical condition appeared more likely to access foods with higher protein content. In years of low white oak acorn production, larger bears and subadults likely turned to alternative food sources. The long-term variation detected in this study was important in identifying which bears were potentially more susceptible to changes in availability of hard mast.

Survival and Conflict Behavior of American Black Bears after Rehabilitation

“…We found that 7.1% of rehabilitated bears in our study engaged in conflict behavior post‐release, which appears similar to conflict rates in the wild (Pelton and Burghardt , Teunissen van Manen et al ). Similarly, Beecham et al () reported that 6.1% of 424 rehabilitated black bears engaged in conflict behavior, and Binks () reported that 3 of 60 (5%) rehabilitated American black bears were shot by landowners because of conflict behavior.…”

Phenological tracking associated with increased salmon consumption by brown bears

“…While there are encompassing theories to begin explaining variation in nitrogen discrimination 31 , we know of no such comprehensive theory for carbon discriminations that likely vary with diet, level of intake, season and animal physiology. Until this issue is resolved, many stable isotope analyses (including this one) have assumed that carbon discrimination is fixed across time and foods 23 – 36 . Despite the sources of uncertainty inherent to stable isotope analyses, percent salmon in assimilated diets was strongly related to estimates of salmon consumption derived from mercury analysis (saturating model, R 2 = 0.69; Fig.…”

“…Nitrogen discriminations used were 5.2 ± 0.5‰ for plant matter and 3.6 ± 0.6‰ for sockeye salmon. We used a constant 3.7 ± 0.2‰ as the carbon discrimination for all foods 23 – 36 . Our models were structured with bear identification number as a random effect, process error, and uninformative priors.…”

Applications of stable isotope analysis in mammalian ecology

“…Teunissen van Manen et al [10] described the use of stable isotopes from fur to compare foraging ecology of wild and captive American black bears (Ursus americanus) that occupy remote areas vs campgrounds and picnic areas in a national park in the southwestern USA. The authors modeled the relationship between δ 13 C and δ 15 N values from bear hair and nine environmental variables.…”