Winter, Spring and Summer Territoriality in Barrow's Goldeneye: Characteristics and Benefits

Abstract

Barrow's Goldeneye Bucephala islandica have a multi-stage territorial system, defending distinct pair, brood, and winter territories. Only paired birds defend winter territories and their territorial behaviour is similar to that observed on the breeding areas. Breeding pair territories averaged 0.44 ha (range: 0.05-1.85 ha) whereas brood territories averaged 0.91 ha (range: 0.27-2.79 ha). Breeding pair territories were not centered around the females but had well defined boundaries, and were defended even when the female was absent. Removal of two pairs suggests that territory size was determined mostly by pair density as territories expanded after the removals. Breeding pair and brood territories averaged approximately 0.35 km from the nest site (range: 0-2.9 km). Broods usually settled on the lake closest to the nest site. Philopatry to breeding pair and brood territories was strong. I suggest that the main advantage of spring and winter pair territoriality may be in providing an exclusive and undisturbed feeding area for the female. Similarly brood territories provide an exclusive feeding area for the young.