Ecological significance of brood-site fidelity in Black Brant: Spatial, annual, and age-related variation

Abstract

We examined use of brood-rearing sites by female Black Brant (Branta bernicla nigricans) that nested at Tutakoke River, Alaska, 1987 to 1993. Adult females exhibited fidelity to brood-rearing sites; however, we observed site-specific and annual variation in movements among sites. Site fidelity of adults was not related to their hatching date, and hatching dates of females did not vary among brood-rearing sites, suggesting that site selection was unaffected by competition. Movement among sites was affected by distance between sites, but this relationship varied annually and among sites. Variation in forage characteristics may affect movements among sites. Natal-site fidelity was equal to fidelity probability of adults, indicating social inheritance of sites and perhaps facilitation through nepotism. We observed heterogeneity in survival probabilities of goslings and adults among sites. For goslings, heterogeneity in survival was probably related to variation in growth. We observed no relationship between hatching date and use of brood-rearing sites. Previously documented seasonal declines in growth of goslings are more likely affected by declines in forage quality and abundance than by site-specific variation in forage characteristics because use of brood-rearing sites was not related to hatching dates.