AGE AND REPRODUCTIVE SUCCESS IN FEMALE LESSER SNOW GEESE - EXPERIENCE, SENESCENCE AND THE COST OF PHILOPATRY

1. We studied age-related reproductive success in female lesser snow geese Chen caerulescens caerulescens, using data from the breeding colony at La Perouse Bay, Manitoba, 1973-88. 2. We assessed age-specific variation in both individual components of reproductive success and their cumulative product using individuals aged 2-19 years. 3. The composite measure of reproductive success increased among birds 2-6 years of age. Increased reproductive success over these ages was due to significant increases in clutch size and gosling survival and significant reductions in probabilities of total nest and total brood failure. 4. After age 6, the composite measure of reproductive success declined significantly. This resulted from a decreased in both hatchability and brood survival, the latter characterized by decreased gosling survival and increased frequency of total brood failure among older birds. The decline in hatchability is most probably due to senescence. 5. The older age decline in reproductive performance with respect to brood-rearing may, in part, reflect senescence of physical abilities needed to competently provide parental care. However, in this philopatric species, the decline may also reflect the tendency of ageing females to continue using specific feeding areas regardless of changes in available forage. Under conditions of systematic deterioration of the environment, philopatric behaviours may become maladaptive.