Major components of grizzly bear diet across North America
Dates
Year
2006
Citation
Mowat, Garth, and Heard, Douglas C., 2006, Major components of grizzly bear diet across North America: Canadian Journal of Zoology/Revue Canadienne de Zoologie, v. 84, no. 3, p. 473-489.
Summary
We measured stable carbon and nitrogen isotope ratios in guard hair of 81 populations of grizzly bears (Ursus arctos L., 1758) across North America and used mixing models to assign diet fractions of salmon, meat derived from terrestrial sources, kokanee (Oncorhynchus nerka (Walbaum in Artedi, 1792)), and plants. In addition, we examined the relationship between skull size and diet of bears killed by people in British Columbia. The majority of carbon and nitrogen assimilated by most coastal grizzly bear populations was derived from salmon, while interior populations usually derived a much smaller fraction of their nutrients from salmon, even in areas with relatively large salmon runs. Terrestrial prey was a large part of the diet where [...]
Summary
We measured stable carbon and nitrogen isotope ratios in guard hair of 81 populations of grizzly bears (Ursus arctos L., 1758) across North America and used mixing models to assign diet fractions of salmon, meat derived from terrestrial sources, kokanee (Oncorhynchus nerka (Walbaum in Artedi, 1792)), and plants. In addition, we examined the relationship between skull size and diet of bears killed by people in British Columbia. The majority of carbon and nitrogen assimilated by most coastal grizzly bear populations was derived from salmon, while interior populations usually derived a much smaller fraction of their nutrients from salmon, even in areas with relatively large salmon runs. Terrestrial prey was a large part of the diet where ungulates were abundant, with the highest fractions observed in the central Arctic, where caribou (Rangifer tarandus (L., 1758)) were very abundant. Bears in some boreal areas, where moose (Alces alces (L., 1758)) were abundant, also ate a lot of meat. Bears in dryer areas with low snowfall tended to have relatively high meat diet fractions, presumably because ungulates are more abundant in such environments. Kokanee were an important food in central British Columbia. In areas where meat was more than about a third of the diet, males and females had similar meat diet fractions, but where meat was a smaller portion of the diet, males usually had higher meat diet fractions than females. Females reached 95% of their average adult skull length by 5 years of age, while males took 8 years. Skull width of male grizzly bears increased throughout life, while this trend was slight in females. Skull size increased with the amount of salmon in the diet, but the influence of terrestrial meat on size was inconclusive. We suggest that the amount of salmon in the diet is functionally related to fitness in grizzly bears.Original Abstract: Nous avons mesure les rapports des isotopes stables de carbone et d'azote dans des poils de garde provenant de 81 populations de grizzlis (Ursus arctos L., 1758) largement reparties en Amerique du Nord et nous avons utilise des modeles de melange pour attribuer les fractions du regime alimentaire correspondant au saumon, A la viande d'origine terrestre, au kokani (Oncorhynchus nerka (Walbaum in Artedi, 1792)) et aux plantes. de plus, nous avons examine la relation entre la taille du crane et le regime alimentaire chez des ours tues par les humains en Colombie-Britannique. la plus grande partie du carbone et de l'azote assimiles par la plupart des populations cotieres de grizzlis provient du saumon, alors que, chez les populations de l'interieur des terres, une fraction beaucoup plus faible des nutriments provient du saumon, meme dans les regions ou les montaisons de saumons sont importantes. Les proies terrestres forment une partie considerable du regime la ou les ongules sont abondants et les proportions les plus importantes s'observent dans la region arctique centrale ou les caribous (Rangifer tarandus (L., 1758)) sont tres nombreux. Les ours de certaines regions boreales riches en orignaux (Alces alces (L., 1758)) consomment aussi beaucoup de viande. Les ours qui habitent les regions plus seches aux precipitations de neige reduites tendent A avoir des fractions importantes de viande dans leur regime, probablement parce que les ongules sont generalement plus nombreux dans ces environnements. Les kokanis sont un element significatif du regime dans le centre de la Colombie- Britannique. Dans les regions ou la viande constitue plus d'environ le tiers du regime, les males et les femelles ont des regimes de composition semblable; cependant, la ou la viande represente une plus petite fraction du regime, les males ont generalement une fraction de viande plus elevee dans leur regime que les femelles. Les femelles atteignent 95 % de leur longueur moyenne de crane vers l'age de cinq ans, alors que les males n'y arrivent qu'A huit ans. la largeur du crane des grizzlis males augmente tout au cours de la vie, alors que cette tendance est peu marquee chez les femelles. la taille du crane augmente en fonction de la quantite de saumon dans le regime, mais l'effet de la viande d'origine terrestre sur la taille n'est pas clair. Nous croyons que la quantite de saumon dans le regime chez les grizzlis est fonctionnellement reliee A la fitness.[Traduit par la Redaction]