Examining hair growth rates and dietary patterns of wild and captive bears

Abstract

The feeding ecology of wildlife has important implications for individual health, population productivity, community structure, and ecosystem functioning. For bears of the family Ursidae, food resources and feeding behavior primarily impact population dynamics via effects on cub production and survival. Much of what is known about the feeding ecology of bears is based on analyses of various tissues collected from capture-based research efforts, harvested animals, or non-invasive approaches. The use of multiple chemical tracer methods provides an informative view of the diet, as each tissue spans a unique timeline. However, inference about diet from hair has been limited by a lack of quantitative data on the timing of the molt and hair growth rates. Addressing physiological assumptions is essential to gain insights into the feeding patterns in wild bear populations in dynamic ecosystems. Climate change is shifting the phenology, availability, and selection of food resources for bears across multiple ecosystems. Because polar bears (Ursus maritimus) specialize in both food and habitat type, they are particularly vulnerable to environmental change. Detailed studies of polar bear foraging are necessary for a comparative and predictive understanding of how diets may change with a loss of sea ice habitat and increased use of coastal habitats. One such documented coastal habitat is freshwater glacier ice, which provides year-round access to prey for Baffin Bay polar bears, although the feeding habits of polar bears using glacier ice relative to those following the retreating ice and/or seasonally moving onshore are not known. This dissertation comprehensively investigates the interpretation of dietary data derived from hair samples and the drivers of diet variability in polar bears, with the overarching goal of contributing to an improved understanding of the feeding ecology of bears. First, methods were developed to document hair growth in three species of captive bears. The methods of hair dye and 13C- and 15N-labeled glycine identified periods of hair growth and detected individual and seasonal variations in hair growth rates, with their effectiveness not being dependent on the bear species. Second, the timing and rate of hair growth were quantified in captive polar bears across an annual cycle, incorporating variables of body location and season. Hair growth was detected at similar rates throughout spring, summer, and fall, while there was slower growth in winter, consistent with the anticipated patterns of an annual molt. Third, dietary patterns among wild polar bears of different sexes, ages, and movement patterns were evaluated in relation to sea ice metrics using stable isotopes and total mercury concentrations in hair. Baffin Bay polar bears showed limited variation in their feeding habits, as indicated by stable isotope values and total mercury concentrations, despite differences in inter-annual sea ice conditions and individual space-use strategies. Fourth, patterns of diet composition were evaluated among Baffin Bay polar bears with distinct coastal and offshore space-use strategies using relative abundances of fatty acid signatures in fat samples, a tissue representing a different time period (winter-fall) than hair (spring-summer). While demographic and short-term temporal variation was minimal, fatty acid signatures and diet estimates clearly differed between coastal polar bears using glacier fronts and offshore bears using pack ice habitat. Collectively, results from these chapters bridge experimental and applied settings, improve interpretations of bear hair samples, and provide insight into the factors driving diet variability in wild polar bears.