Breeding dispersal in the Tree Swallow (Tachycineta bicolor).

WINKLER, DAVID W.; WREGE, PETER H.; LLAMBÍAS PAULO E; FERRETTI VALENTINA

Ithaca

Congreso; Annual Meeting of the Association of Field Ornithologists and the Wilson Ornithological Society; 2004

To study the patterns and determinants of breeding dispersal in Tachycineta bicolor we analyzedthe records of 323 male and 773 female captures in more than one breeding season in our study areas near Ithaca, New York. Our study populations are split into six "Units" of concentrated nest-boxes, and we analyze dispersal as the change in breeding site both within and between Units in different years. No birds were ever found to disperse into or out of the Units to/from a more diffuse network of boxes and banders throughout the surrounding regions of New York State. Only 1 male was ever found to disperse from one Unit to another when boxes at his original Unit remained available. Of the 773 female records, 55 (7.1%) switched breeding Units between years. We present evidence that the probability of dispersing to a given Unit declines as the distance to that Unit increases, and we also find that females that failed to fledge any offspring are much more likely to disperse than are those females that were reproductively successful. We suggest that the spatial scale in which swallows gather and process information is much larger than that for passerines that defend all purpose territories.