Long-Term Decline in Fecundity in a Snow Goose Population: Evidence for Density Dependence?

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Abstract
(1) A population of lesser snow geese (Chen caerulescens caerulescens L.) has been studied at the breeding colony at La Perouse Bay, Manitoba [Canada], from 1968 to the present. (2) Annual mean clutch size, when adjusted for annual variation in mean laying date and intraspecific nest parasitism, has declined significantly by 0.72 eggs, or 16% of the initial annual mean, over the period of the study. Annual rates of eggs lost due to predation, egg hatchability, and fledging success had remained unchanged. (3) The rate of long-term decline in mean clutch size was independent of female age and breeding experience, and was not related to systematic changes in the age-structure of the breeding population. Individual females had clutch size declines parallel to the decline of the population mean. (4) Mean clutch size is negatively correlated with the size of both the breeding colony and the total flyway population, both of which have increased significantly. The decline in clutch size may reflect increased intraspecific competition for food during spring migration.