Studies of migration have revealed multiple trade‐offs with other life‐history traits that may underlie observed variation in migratory properties among ages and sexes. To assess whether, and to what extent, body size and/or sex‐specific differences in competition for resources (e.g. breeding territories or winter food) may shape variation in migration distance and timing of arrival in ecologically and phylogenetically related species, we combined over 30 000 sightings of individually marked, sexually mature males and females of Herring GullsLarus argentatusand Lesser Black‐Backed GullsLarus fuscuswith biometric measurements and phenological observations at a mixed breeding colony. InL. argentatus, larger males migrated further from the breeding colony, whereas migration distance was independent of body size in adult females. InL. fuscus, no relationship between body size and migration distance was apparent in either sex. Mean arrival dates at the breeding colony did not vary with migration distances but differed between males and females ofL. argentatus(but notL. fuscus). As allometry at least partly explains sexual segregation in migration behaviour inL. argentatus, but not inL. fuscus, we conclude that the effect of body size on sex‐related migratory strategies may vary between closely related, sympatric species despite similar size dimorphism.
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Bosman et al. (2011) studied this question.
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