Use of artificial eggs to determine egg losses and predation in a Neotropical passerine

SVAGELJ, W. S.; MERMOZ, M. E.; FERRETTI, V.; FERNÁNDEZ, G. J.

New Orleans, USA

Congreso; 3rd North American Ornithological Conference; 2002

Ornithological Societies of North America

We used artificial nests baited with either Quail (Coturnix coturnix) or Shiny Cowbird (Molothrus bonariensis) eggs to identify predators, and quantify the predation risk of a Neotropical passerine. Nest and egg survival of artificial nests were compared to those active nests of the Brown-and-yellow Marshbird (Pseudoleistes virescens). Experimental nests baited with Quail eggs suffered lower predation and egg losses than those baited with Cowbird eggs. The main cause of egg losses and nest mortality in Cowbird-baited nests was pecking behavior of the own Cowbirds. Differences still hold when we removed the effect of Cowbirds from the analysis. In this area the Shiny Cowbird constitutes one of the main factors that cause the reduction of breeding success of several host species. Quail-baited nests had higher nest and egg survival than active Brown-and-yellow Marshbird nests, whereas Cowbird-baited nests had lower nest and egg survival than active nests. We attributed such differences to parental defense. In conclusion, nests baited with passerine eggs, as cowbirds´, are more likely to document accurately the probability of nest detection by predators suffered by passerines in an area with high density of Cowbirds.