Correlations and Depletion Patterns of Marrow Fat in Caribou Bones

Abstract

We used linear regression to examine the relationship between femur marrow fat and marrow fat of the other 5 long leg bones (tibia, metatarsus, humerus, radius, and metacarpus) and mandibles using paired bones from individual caribou (Rangifer tarandus granti) in Alaska [USA]. Correlations were high in all regressions (range of r= 0.90-0.98) and suggested that all bones were useful as gross indices to relative body condition. However, when interpreting fat content of bones other than femurs and making between-bone comparisons, there is merit in indexing fat values to a "femur standard". The percent marrow fat in all leg bones of individual caribou was more uniform than in moose (Alces alces). The sequence of fat depletion in caribou long bones was closer to that of moose than other wild ungulates. Fat depletion in both moose and caribou advances more rapidly in proximal long bones than in more distal ones. Mandible marrow fat can be used as a relative condition index if limitations are recognized.