Shiny cowbird brood parasitism on White-rumped Swallow

V. MASSONI; WINKLER, D.; JUAN C. REBOREDA

JOURNAL OF FIELD ORNITHOLOGY

Año: 2006 vol. 77 p. 80 - 84

0273-8570

Swallows and martins are infrequent hosts of the generalist brood parasite Shiny Cowbird (Molothrus bonariensis). We monitored 50 nesting attempts by White-rumped Swallows (Tachycineta leucorrhoa) over a two-year period in Argentina and detected low rates of brood parasitism (three nests, or 6%). Of the three nests parasitized, cowbirds (N = 1 per nest) successfully fledged from two. Eight of 13 swallow eggs in these three nests were punctured by cowbirds, and all but one swallow nesting starved at the two parasitized nests. At least two factors may contribute to the low frequency of parasitism of White-rumped Swallows by Shiny Cowbirds, including the inability of the larger cowbirds to enter some nest cavities and the aggressive nest defense behavior of adult swallows.