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Territorial behaviour, nesting success and brood survival in Barrow's Goldeneye and its congeners Savard, Jean-Pierre L.


In this study, I first describe and characterize the intra- and interspecific territorial behaviour of Barrow's Goldeneye (Bucephala islandica) and compare it to that of Common Goldeneye (B. clangula) and Bufflehead (B. albeola). Second, I examine some factors influencing the use of nest boxes by Barrow's Goldeneye and their reproductive success. Finally, I compare duckling mortality in Barrow's Goldeneye and Bufflehead. Barrow's Goldeneye, Common Goldeneye and Bufflehead pairs have similar territorial behaviour: they defend a fixed, exclusive area against rivals. Pairs are also interspecifically territorial during the breeding season, and interspecific aggression is strongest toward congeners and stronger toward diving ducks than toward dabbling ducks. The degree of aggression shown is correlated with the degree of overlap in diet and foraging modes. Barrow's Goldeneye and Bufflehead females are intra- and interspecifically aggressive after their young have hatched and their behaviour is similar to that of the drakes in the spring. Brood amalgamation is frequent in Barrow's Goldeneye and is an accidental outcome of territorial encounters between broods. Barrow's Goldeneye pairs also defend intra- and interspecific territories on the wintering areas. Philopatry to summer and probably also to winter territories is strong in Barrow's Goldeneye. Barrow's Goldeneye maintain monogamous long-term pair bonds but are occasionally polygynous. Provision of nest boxes resulted in an increase in breeding densities of Barrow's Goldeneye. Factors that influenced the use of nest boxes by Barrow's Goldeneye included: previous use of the nest box, outcome of the previous breeding attempt, age of the nest box and its location. Proportions of nest boxes that hatched, were preyed upon and were deserted, averaged respectively 46±4% (S.E.), 31±3% and 23±3% (n=4 years). Minimum estimates of intraspecific nest parasitism ranged between 5% and 20%. The daily mortality rate of Barrow's Goldeneye and Bufflehead ducklings varied with years, duckling age and hatching date. Mortality rates were highest in the first week following hatching. In years of high mortality, broods that hatched early tended to survive better than late hatching broods. Barrow's Goldeneye ducklings had a higher daily mortality rate than Bufflehead ducklings. The main function of territoriality in these species seems to be the provision of an exclusive feeding area for the female or the young. I argue that the evolution of interspecific aggression in the genus Bucephala has been favoured by a high level of intraspecific aggression within the genus and significant feeding advantages obtained from the exclusion of competitors. The genus Bucephala provides one of the best examples of interference competition in a guild of related competitors.

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