The importance of meat, particularly salmon, to body size, population productivity, and conservation of North American brown bears

We hypothesized that the relative availability of meat, indicated by contri bution to the diet, would be positively related to body size and population productivity of North American brown, or grizzly, bears (Ui;rus arctos). D ietary contributions of plane matter and meat derived from both;terrestrial and marine sources, were quantified by stable-isotope analysis (delta(13)C and delta(15)N) Of hair samples from 13 brown bear populations. Estimates of adult female body mass, mean litter size, and population density were ob tained from two field studies of ours and from other published reports. The populations ranged from largely vegetarian to largely carnivorous, and foo d resources ranged from mostly terrestrial to mostly marine (salmon, Oncorh yachus spp.). The proportion of meat in the diet was significantly correlat ed with mean adult female body mass (r = 0.87, P < 0.01), mean litter size (r = 0.72, P < 0.01), and mean population density (r = 0.91, P < 0.01). Sal mon was the most important source of meat for the largest, most carnivorous bears and most productive populations. We conclude that availability of me at, particularly salmon; greatly influences habitat quality for brown bears at both the individual level and the population lever.