Current Diets

Diet can be understood--and visualized--in several different ways. We humans concieve of our diet in very literal and concrete ways, as well as in ways that are more abstract or functional. As literal as cheese or spinach or tacos, or as abstract as calories, or something in between, such as proportions of protein and hydrogenated fats. Those in the medical community focus on the more abstract reckonings because these are more directly relevant to health and nutrition. But, inevitably, the abstractions need to be translated by someone into the food that is put on the table.

 

Given the merit attached to different reckonings, I've tried to present information on the diets of contemporary grizzly bear in various ways--from the more literal to the more abstract. In this section I describe diets of North American grizzlies in taxonomic terms, as species of food items, cast as gradients from north to south--from the arctic to temperate regions of the contiguous US. On the page devoted to a more functional representation of diet (Current diets II), I feature Yellowstone's grizzly bears, and illustrate the conversion of taxonomic items detected in scats to an assessment of diet energy and nutrient content, both by season and totaled for the entire year (you can find more on that aspect of things under Nutrition). Finally, on the third page of Current Diets I focus on the contribution of terrestrial meat to grizzly bear diets throughout North America, emphasizing an explanation of patterns. A final note: My emphasis throughout is on diets of grizzly bears inland of the dominant influence of spawning salmonids on the diets of coastal brown bears. So, on to taxonomic gradients...  

The graphs on this page are based on a review of all the diet studies of North American grizzlies that have been reported in one form or another--in journal papers, theses, dissertations, or project reports. I scored each taxonomic diet item as heavily consumed (3), moderately heavily consumed (2), or of lesser importance (1). I resorted to a subjective scoring because the taxonomic composition of diets has been reported in so many largely incompatible ways--as frequencies, as relative volumes, as "corrected" volumes, and broken out annually or by seasons with highly varied demarcations and durations. Once I had summarized these scores, I ordinated the studies by latitude, from north to south (rows), and by the prominance of each diet item as one moved from north to south (columns). I then generated a moving average of scores for each item, moving north to south. The values in the taxon-specific graphs on this page are the moving averages, with each taxon illustrated by a photo in hopes of making these taxonomic abstractions a little more concrete.

The graphs to the right shows trends in the consumption of various vertebrates by North American grizzlies, again ordinated from north to south, from the arctic North Slope to the Rocky Mountains of Wyoming and Montana.