Reproductive Habits in the Snow Goose: The Influence of Female Age

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Abstract
An intensive banding program over several years at La Perouse Bay, Manitoba [Canada] established a marked population of female snow geese [Anser caerulescens caerulescens] of known age. Some females began nesting as 2 yr olds but others delayed 1st nesting until at least 4 yr of age. Year-class differences seemed to occur in the average age of recruitment to the nesting segment and in the patter of return. Differences in the availability of nutrients to goslings could influence subsequent performance of a year-class. Young females nested predominantly in areas of the colony recently colonized irregularly available for nesting. Nest density was lower where young birds were concentrated. Young females nested later than adults and clutch size was lower. Difference between year-classes in the timing and clutch size of 3 yr old females suggested that experience, as well as age itself, could be a factor. Young birds did not have smaller clutches simply because of where or when they nested relative to adults. Even in areas of the colony dominated by young birds, adults nested earlier and had larger clutches. Average clutch size decreased as the season progressed. This relationship held when single age classes were examined, showing that the relationship was not an artifact of age structure of the population. Consideration of the selective pressures which could result in deferred maturity and lower clutch sizes among young nesting females led to the conclusion that experience must be a factor. Feeding efficiency was not likely to be the critical factor requiring learning in this grazing species. Nutrient reserves of a young female on arrival at the nesting colony were likely to be low relative to adults, although this had yet to be demonstrated. Although body condition could act as the proximate factor influencing clutch size and timing, the ultimate factors on which selection acted could be different. Mechanisms and causes of reproductive regulation in this species need to be determined.

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