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Some aspects of dominance behavior in the song sparrow, (Melospiza melodia) Arcese, Peter


I studied the effect of behavioral dominance on survival and recruitment in the song sparrow (Melospiza melodia). The aims of this study were: 1) to determine if superior dominance status allows high survival and priority of access to breeding territory; 2) to measure the influence of phenotypic characters on dominance status; 3) to test the hypothesis that familiarity with a site is a prerequisite to achieving dominant status. Dominance was estimated by observing the agonistic encounters of young sparrows at feeders, and this estimate was correlated with the subsequent survival and settlement of yearlings. Correlations were also sought between dominance and several characteristics of individuals. To study site attachment, I temporarily confined 24 early-hatched birds in two groups. This allowed them experience in agonistic encounters, but prevented them from gaining site attachments until all young birds had become independent. The dominance of these captive birds was estimated after their release and compared to that of control birds. In both sexes, higher proportions of dominants survived and settled than subordinates in each year of study. Only age and sex were consistently correlated with dominance; young hatched early were dominant to those hatched later, and males were more dominant than females. Overall, age accounted for 59% of the variation in dominance. Captive males and females were as dominant as control young of equal age, and were dominant to birds hatched later. These results support the hypotheses that dominant status in song sparrows allows high survival and priority of access to a breeding territory. Natural selection should favor parents that raise many early offspring. Familiarity with a local area was not a prerequisite to achieving dominant status. The assumption that large size is advantageous in agonistic encounters was not supported by this study, and a review of the literature suggests that many studies that support this assumption are based on inadequate analyses.

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