Mass emigration of Arctic Tundra caribou from a traditional winter range: Population dynamics and physical condition

Major declines of populations of caribou and reindeer (Rangifer tarandus) t hat permanently reside on Arctic tundra have been attributed to short-term inaccessibility of forage through restrictive snow cover. Such density-inde pendent phenomena would produce unpredictable changes in populations of Arc tic tundra caribou, In 1985, Inuit correctly predicted mass emigration from the winter range of a caribou subpopulation on Fore Peninsula (FP, souther n Baffin Island, Canada. During 1982-94, we conducted aerial surveys, satel lite telemetry: and physical condition studies to examine features of the p redicted range shift. Between 1984 and 1992, caribou density oil upland ter rain on FP dropped (P < 0.001) from 6.2 to 0.3 caribou/km(2). Cows began to emigrate en masse during winter 1988-89 (P = 0.10) toward Meta Incognita P eninsula (MIP), where caribou showed greater fidelity to thai wintering are a during 1988-94 (P = 0.005). Density of caribou on upland. terrain on PI M IP increased (P = 0.001) from 0.2 to 5.0 caribou/km(2) between 1982 and 199 2. In April 1992, body size did not differ (P greater than or equal to 0.47 ) between FP and MIP. Cows on MIP had. greater (P less than or equal to 0.0 4) fat and muscle reserves than cows on FP while only fat reserves of MIP b ulls were greater than (P less than or equal to 0.03) those of FP bulls. Ou r results support Inuit observations of declining physical condition of FP caribou in the early 1980's, and their view that the range shift was caused by cumulative annual overgrazing of the winter range during the previous 1 0 to 30 yr. Fewer cows on FP were pregnant (2 of 8) than on MIP (10 of 10: P = 0.002). Calf:cow ratios were higher (P = 0.05) on MIP than on FP in 199 2. Although few caribou had occupied MIP for 50 yr before 1988-89. MIP cari bou were in relatively poor condition by April 1992 compared to those on ov ergrazed Coats Island during mild. winters. Winter range shifts and populat ion declines by Arctic tundra caribou may be predictable. Ecological indica tors ma) enable managers to mitigate the effects of overgrazing on caribou populations through intensive harvesting at critical stages during long-ter m population increases.