Demography of the Porcupine caribou herd, 1983–1992

Abstract

Population size, parturition rates, and sex- and age-specific survival rates were determined for the Porcupine caribou herd (Rangifer tarandus granti) in northeastern Alaska and northwestern Canada between 1983 and 1992. The herd increased at an annual rate of r = 0.0467 between censuses in July 1983 (n = 135 000), July 1987 (n = 165 000), and July 1989 (n = 178 000). The mean parturition rate for 225 radio-collared cows aged ≥3 years monitored for 603 reproductive attempts between 1982 and 1992 was 80% and did not differ among years. First-year survival of calves was 51%. The survival rate of calves through their first month differed among years (range 57–90%). The mean annual survival rate for ≥3-year-old caribou was 84.2% for 225 females and 82.6% for 42 males. Hunting mortality for the herd averaged 2–3% annually. Population estimates generated by a computer model using parturition and survival rates for the herd closely tracked population trends determined from photocensus data. Growth of the herd is most sensitive to the survival of females 3 years of age and older, followed by calf production and survival.