Yellow warbler (Dendroica petechia) breeding biology and parasitism by the shiny cowbird (Molothrus bonariensis ) in Boqueron, Puerto Rico

Aspects of the breeding biology of the Yellow Warbler (Dendroica petechia) and Shiny Cowbird (Molothrus bonariensis) parasitism were studied in Boqueron, Puerto Rico from 2001 to 2002. Fifty-seven percent (n = 12) of warbler nests were parasitized. Survival of parasitized nests was lower than non-parasitized nests. Thirty-four percent of nests (n = 21) survived until fledging of cowbird or warbler chicks, with predation the major cause of nest failure (88%). Nineteen nests fledged warbler young and two nests fledged cowbird young, but no nest fledged warbler and cowbird young simultaneously. The Yellow Warbler presented three responses toward parasitism: acceptance and incubation, egg burial, and nest desertion. No warbler young fledged from nests that accepted parasitism. Nests with buried cowbird eggs fledged an average of 2.00 +/- 1.41 warbler chicks. This study shows that the Yellow Warbler in Puerto Rico expressed anti-parasite strategies three decades after first contact with the Shiny Cowbird.