Population Parameters of Thick-Billed Murres at Coats Island, Northwest Territories, Canada

Abstract

About 100 adult and 2,000 nestling Thick-billed Murres were banded at Coats Island annually since 1984. Intensive efforts were made in 1990-1993 to estimate the reproductive success of birds of known age and to record the band numbers of as many birds as possible. Adult annual survival, estimated from the numbers of banded birds resighted, was 87% for females and 89% for males. A capture-recapture estimate for the sexes combined gave a mean annual survival of 89%. The youngest age at first breeding was three years, 60% of birds bred at five or younger and nearly 90% at six or younger. Females started to breed about one year earlier than males. Those birds breeding at less than seven years old had a lower apparent survival rate than older breeders. Approximately 50% of chicks that left the colony were resighted again at three years or older. In each year, the mean success of pairs consisting of two experienced breeders, or of one experienced and one unbanded bird was always higher than that of pairs including young birds of relatively less experience. Reproductive success increased with age to at least nine years. The survival of breeding murres from Coats Island, and those from colonies in Greenland, both of which populations are subject to heavy hunting in their wintering area, is generally lower than survival rates of Common Murres populations in Europe and North America, where hunting pressure on breeders is lower. The proportion of birds banded as nestlings that were seen at the colony at three years or older was high compared to Common Murres in Europe. The high survival rate of young birds is apparently sufficient to offset the additional mortality caused by hunting.