Body-size comparisons of alpine- and forest-wintering woodland caribou herds in the Yukon

Information from radiotelemetry studies has shown that woodland caribou (Ra ngifer tarandus caribou) living in the snow-shadow region of the southwest part of the Yukon spend part of the winter in the subalpine and alpine zone s. Other woodland caribou living in areas with high snowfall in central and eastern Yukon have traditional winter ranges in forested lowlands. We theo rize that selective forces exerted by the wintering environments will have induced differences in caribou body characteristics, and we test the hypoth esis that woodland caribou that winter in the alpine zone are phenotypicall y different from those wintering in forested environments. We compared five physical measurements from 382 female woodland caribou in 11 Yukon herds. Our results indicate a significant (14 cm) difference in shoulder height be tween forest- and alpine-wintering groups, but provide no support for the h ypothesis that the difference is due to snow depth. There were no significa nt differences in other body measurements or in body proportions. It is als o unlikely that the difference in shoulder height is due to winter nutritio n, since body condition scores did not differ between forest- and alpine-wi ntering groups. We discuss seasonal nutrition, predation, and migration as alternative explanations for our results.