Evaluation of a mountain sheep transplant in north-central Montana

Published source details Irby L.R. & Andryk T.A. (1987) Evaluation of a mountain sheep transplant in north-central Montana. Journal of Environmental Management, 24, 337-346.
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This study is summarised as evidence for the following.

	Action	Category
	Release translocated/captive-bred mammals in family/social groups Action Link

Release translocated/captive-bred mammals in family/social groups

A study in 1960–1985 of forest and grassland across a mountain range in Montana, USA (Irby & Andryk 1987) found that a translocated population of Rocky Mountain bighorn sheep Ovis canadensis released in groups increased at rate similar to that of a population newly established through natural recolonization. Following translocation of 37 adult sheep and 30 lambs, the population reached 54 sheep and 43 lambs seven years later, though was estimated at 31 sheep and 12 lambs the following year. A naturally recolonized population increased from 30 sheep at establishment to 77 sheep and 49 lambs 22 years later (the same year that the population peaked in the translocated population) though declined to 33 sheep and 15 lambs the following year. Sheep populations were studied in a 3,000-km² study area. The translocated population (released in 1976) was surveyed seven times between 1976 and 1985. The recolonized population (established in 1958–1960 and occupying a separate part of the study area) was surveyed 11 times between 1960 and 1985. Surveys were carried out on the ground or by helicopter, usually on winter ranges. Weather frequently hampered surveys of the translocated population.

(Summarised by: Nick Littlewood)