Reproduction and survival of brown bears in southwest Alaska, USA

Abstract

From June 1993 to June 2003, 40 adult female brown bears (Ursus arctos) were captured, radiocollared, and tracked for 1 to 10 years in a previously unstudied population in southwest Alaska. Mean litter size upon emergence from dens was 2.0, decreasing to 1.5 at weaning. Mean age of offspring at weaning was 2.9. Mean age of primiparity was 7.2 years while first weaning was estimated at 9.5 years. Mean maximum age of a female weaning a litter was 27.3 years. Mean annual survival estimates were 90.1–97.2% for radiocollared females ≥5 years old, 48.2–61.7% for cubs of the year, and 73.3–83.8% for 1 and 2-year-old offspring combined. Of 129 offspring followed beginning with their first summer, 38 (29.5%) survived to be weaned. Hunters harvested at least 12 marked or radiocollared bears (9 males and 3 females). No defense of life and property (DLP) killings were reported within or near the study area, but illegal harvests of brown bears were known to have occurred in the general region. Harvests within or near the study area averaged 7.3–12.1 males/year and 4.8–5.2 females/year. This population's rate of increase (λ) was estimated as 1.035–1.047 for the first half of the study, 0.963–0.997 for the second half, and was found to be most sensitive to survival of females 5–14 years old.