Protandrous migration and variation in morphological characters in Emberiza buntings at an East Asian stopover site

Abstract

The effect of the timing of spring migration on reproductive success differs between the sexes. As a consequence, various sex-specific tactics relating to the timing of migration have evolved in migratory avian groups. Various hypotheses have been proposed to explain differential migration to breeding or wintering grounds, and inter- and intrasexual size differences are often considered one of the proximate mechanisms. We investigated arrival patterns in the spring by individuals of each sex, sexual size dimorphism and related morphological variables, and the relationship between size variation and arrival date in five bunting species that passed through an East Asian migratory flyway stopover site in 2006–08. Males of all the study species arrived before females, and significant sexual dimorphism was observed. Several morphological characters, including total length, wing-length and tail-length, contributed to the size variation. Although larger males arrived earlier, there was no relationship between arrival date and size in females. Our study confirmed that East Asian buntings display a discriminated protandrous migration pattern at the stopover site as well as at the breeding grounds. This is consistent with the view that larger body size in males is favoured due to its association with early arrival to help ensure access to the best resources and hence enhanced mating success.