Official journal of the Netherlands Ornithologists' Union
|Veit R.R. (1997) Long-distance dispersal and population growth of the Yellow-headed Blackbird Xanthocephalus xanthocephalus. ARDEA 85 (1): 135-143
|In this paper, I sought to account for inter-annual variability in the frequency with which Yellow-headed Blackbirds disperse eastwards from the core area of their breeding range to the east coast of North America. It is hypothesized that eastwards dispersal is a consequence of enhanced reproduction, that is, the number of Yellow-headed Blackbirds recorded during a given autumn migration at the east coast is related to the number of offspring produced within the breeding range. The major premise of this study was that the tendency for any individual to disperse is constant, so that larger numbers of individuals moving east during any autumn reflects larger numbers of young having been produced the previous summer (most individuals found at the east coast have been juveniles). Records of vagrant Yellow-headed Blackbirds from Massachusetts and elsewere within eastern North America were used to estimate the yearly magnitude of dispersal, and data from the US Fish and Wildlife Service's Breeding Bird Survey (BBS) to estimate annual reproduction. Eastwards dispersal of Yellowheaded Blackbirds was strongly coherent throughout the Eastern United States, which is consistent with the notion that vagrancy is a consequence of a broad-scale, population-level process such as reproduction. Dispersal was also significantly related to reproductive success in the north central North America. Thus, the number of Yellow-headed Blackbirds recorded in Massachusetts during a given autumn was significantly related to estimated reproductive success at the northern and eastern periphery of the breeding range. the same area where growth and spread of the population has been most evident.