Colonial Nesters in a Deteriorating Habitat: Site Fidelity and Colony Dynamics of Lesser Snow Geese

Birds that exhibit a high degree of natal and breeding philopatry and nor- mally breed in stable environments may suffer costs of philopatry if their habitat deterio- rates. Female Lesser Snow Geese (Chen caerulescens caerulescens) are highly site faithful; how- ever, recent increases in numbers of breeding birds have resulted in widespread habitat de- struction in some colonies. Using capture-recapture modeling techniques on multiple re- sightings of marked individuals, we examined whether breeding-site fidelity of adult Snow Geese has changed over time in a colony that has grown rapidly and in which habitat quality has declined severely during the past two decades. In addition, we examined the age struc- ture of breeding birds to investigate natal-site fidelity to formerly central areas of the colony. Only slight changes in adult breeding-site fidelity were detected over 10-year periods, de- spite the deterioration of nesting and brood-rearing habitats in and near the investigated areas. However, increasing mean ages of breeding birds in formerly central areas of the col- ony indicated a lack of recruitment into those areas; young birds must have preferred to settle at the colony periphery even when vacant spaces in the center were available. Together with a small amount of movement by adult birds, the settlement pattern of young birds has led to a long-term shift in the colony location as a whole. Received 12 June 1997, accepted 5 December 1997.