Population characteristics of the Burwash caribou herd in the southwestern Yukon estimated by capture–recapture analysis

Seasonal censuses (calving, rut, and winter periods) and other surveys were undertaken to apportion changes in mountain caribou (Rangifer tarandus caribou) numbers to changes in mortality, recruitment or ingress–egress, and to assess seasonal distribution. Data were collected from September 1978 to June 1982 in the St. Elias Mountains of the southwestern Yukon. Thirty-nine caribou were radiocollared and used in capture–recapture analysis. Estimates varied from a minimum herd size of 330 to a maximum of 560. Bulls comprised 33% of animals older than calves. Calving occurred between 15 May and 13 June from 1979 to 1982. Pregnancy rates varied from 78 to 82% during 1980 to 1982 while calves comprised 20% of the herd in calving periods, 19% during ruts, and 18% during midwinters. Recruitment (% yearlings) varied from 9% in 1980 to 13% in 1981 and 14% in 1982. Neonate mortality (birth to 3.5 weeks) varied from 13 to 49% between 1980 and 1982. An average of 56% of calves died within 5 months of birth. Natural mortality rates of adult–subadults varied between 6 and 9%. All evidence indicated stable or slowly increasing numbers until winter 1982 when movement from the study area was documented. The total range size was 1978 km2 with the herd occupying two distinct seasonal ranges in upland tundra plateaux separated by lowland boreal forest. Herd densities (based on seasonal range size) averaged 1.66 caribou/km2. The proportion of the herd in each upland area varied consistently between seasons and years such that variations in numbers could be accounted for by mortality, recruitment, and movement from the study area in the winter of 1982.