Long-Term Changes in Survival Rates of Lesser Snow Geese

Survival rates of adult and juvenile Lesser Snow Geese (Anser caerulescens caerulescens) were estimated based on hunter recoveries from over 80 000 geese banded between 1970 and 1988 at La Perouse Bay, near Churchill, Manitoba. Adult survival rate increased significantly from -78% in 1970 to nearly 88% in 1987. Similar increases in adult survival, although not significant, occurred between 1969 and 1979 at a second colony of Snow Geese at Cape Henrietta Maria in Northern Ontario. These increases coincided with a decline in the proportion of Snow Geese being shot each year on the flyways, suggesting that reduced mortality from hunting may be responsible for the increased sur- vival. In contrast, survival rates of fledglings over their first year decreased significantly from a mean of 60% in 1970 to -30% in 1987, despite the reduction in hunting pressure. This indicates that young geese have been suffering increasing rates of nonhunting mortality, most likely prior to leaving the breeding grounds or on their first autumn migration. Their increased mortality appears to be related to slower growth rates and reduced body size induced by deteriorating feeding conditions on the breeding grounds. This study shows that different processes can influence mortality rates at different stages of the life cycle. The long-term changes indicate that mean values of age-specific survival rates are not adequate to describe the dynamics of this population.