Calf production and overwinter survival estimates for Peary Caribou, Rangifer tarandus pearyi, on Banks Island, Northwest territories

Abstract

In response to declining numbers of Peary Caribou (Rangifer tarandus pearyi) on Banks Island, sex and age classification surveys were conducted systematically from 1993-1999. Previous surveys (1982-1991) had been conducted sporadically. We compiled all data to estimate calf production (ratio of calves per 100 ≥ 2 year-old females) and overwinter survival. Calf production, estimated for 11 years, ranged from 24.0 to 75.6 and was ≥ 50.0 in eight years. Overwinter survival, estimated for seven years, ranged from 23-86% and was ≥ 50% in four years. We partitioned classification data into five different circannual periods: calving (May and June; n = 5), summer (July and August; n = 8), fall/rut (September through 10 November; n = 5), winter (11 November through March; n = 8), and pre-calving (April; n = 3). A Kruskal-Wallis analysis indicated year effects (P=0.06) on the ratio of calves per 100 ≥ 2 year-old females; ratios were higher during 1995, 1996, and 1999. There was no relationship between reduced calf production or overwinter survival and increased snow depth or hardness. The drop in number of Banks Island Caribou (≥ 1 year-old) from 709 (SE 128) in 1994 to 436 (SE 71) in 1998 has happened despite high calf production, high overwinter survival of calves, and less severe winter snow conditions.