Restoration of a large vertebrate to regions of former range was an opportunity to study processes of population expansion and colonization. Muskoxen (Ocibos moschatus) were returned to the Arctic National Wildlife Refuge (Arctic NWR) in northeastern Alaska in 1969-70, after an absence of over 100 years., In 1982-95, I documented changes in distribution and abundance of muskoxen and determined the relative importance of calf production, survival, and emigration on abundance in regions first occupied. I used annual censuses, counts of sex and age classes, and radiotelemetry surveys to determine exponential rates of increase and range expansion. From 1977 to 1981, muskoxen increased ai an annual rate of 0.24, and calf production averaged 87 calves/100 adult females. From 1982 to 1986, mixed-sex groups still occupied the same regions, but annual rates of increase declined to 0.14 and calf production declined to 61 calves/100 adult females. After 1986, numbers of muskoxen in regions first occupied declined and may be stabilizing at <300 animals. Calf production continued to decline (49 calves/100 ad F in 1987-90 and 38 calves/100 ad F in 1991-96). Rates of calf and yearling survival did not decline but were negatively correlated with snow depth in late spring. After 1986, dispersal of mixed-sex groups into other regions also contributed to the decline in muskox numbers in regions first occupied. In 1995, 647 muskoxen were seen in the study area from the Sagavanirktok River to the Clarence River. Throughout the total range of mixed-sex groups, about 800 muskoxen were observed in the 500 km between the Itkillik River west of Prudhoe Bay and the Babbage River in northwestern Canada., Muskox range expansion, population trends, and interactions with caribou (Rangifer tarandus) should continue to be monitored.
