Settlement into Breeding Habitats by Barrow's Goldeneyes Bucephala islandica: Evidence for Temporary Oversaturation of Preferred Habitat

Abstract

The paper describes spatio-temporal patterns of settlement into different habitats by territorial pairs of Barrow's Goldeneye at Lake Myvatn and River Laxai, Iceland, in spring. Locally, a preference for a habitat, as reflected by timing and rate of settlement and final density of pairs, could be predicted by density of potential food. Settlement followed a pattern which suggested preferred habitats were saturated. In rich habitats numbers of territorial pairs increased to a peak but decreased again before egglaying commenced. This decline could not be accounted for by a decline in food supply or redistribution of pairs due to ice break-up. This suggests that the decline represents a final adjustment of density after the habitat has become temporarily overcrowded. Territories were classified as either inshore or offshore, the latter being more costly to defend, smaller, set up later and eventually abandoned. Density of potential food was similar in both types of territory but inshore birds spent a lower proportion of time foraging.