Individual study: Calf mortality and population growth in the Delta caribou herd after wolf control
Valkenburg P., McNay M.E. & Dale B.W. (2004) Calf mortality and population growth in the Delta caribou herd after wolf control. Wildlife Society Bulletin, 32, 746-756
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Remove or control predators
A controlled, before-and-after study in 1990–2000 in alpine tundra and subalpine shrubland in Alaska, USA (Valkenburg et al. 2004) found that wolf Canis lupus culling did not increase calf survival or population size of caribou Rangifer tarandus. Between 1992-1993 (before the wolf cull) and 1994-1995 (after the cull), the increase in calf:cow ratio within the cull area (before: 7.4:100; after: 21.5:100) was no greater than in a similar sized herd in an area without wolf culling (before: 11.2:100; after: 19.5:100). However, the change was greater than in a smaller sized herd in an area without wolf culling, where the calf:cow ratio declined (before: 15.8:100; after: 11.5:100). The long-term (1993–2000) change in caribou numbers in the population where wolves were controlled (before: 3,661; after: 3,227) was comparable to the population change in one of the areas without culling (before: 1,970; after: 1,730), but not to the other (before: 500; after: 675), although no statistical tests were carried out. Autumn calf:cow ratios were monitored annually between 1990 and 2000 from a helicopter, guided by radio-collared females. See original paper for methods for estimating population size. In 1993–1994, 60–62% of wolves were controlled by trapping, snaring and shooting. Smaller numbers (20–40%) were culled in subsequent years by local hunters.
(Summarised by Ricardo Rocha)