The caribou (Rangifer tarandus) of Arctic Alaska are gregarious, frequently mobile and occupy environment too harsh to support more than a limited spectrum of specialized animals. Although most previous work on caribou has been conducted during the short summer phase of their environment, Lent (1966) has summarized the annual ecology of the study population, which he estimated to contain from 160,000 to 200,000 animals. He described a movement pattern which showed that summer distribution was largely to the north of the Brooks Range watersheds following migrations through the mountains which lasted from April into June. Reverse migrations occurred in late August and by late November caribou were established on their principal wintering grounds along the Kobuk River drainage, where the northern limit taiga extends its fingers into the southern slopes of the Brooks Range.