Effect of cowbird parasitism on brood reduction in the Brown-and-yellw Marshbird

DURÉ-RUIZ, NATALIA; MERMOZ, M. E.; FERNÁNDEZ, G. J..

THE CONDOR

Cooper Ornithological Sopciety

Año: 2008 vol. 110 p. 507 - 513

0010-5422

    Brood parasitism usually imposes several costs to individual hosts. One of these costs is the increase of the probability of brood reduction. In this paper we analyzed the effect of cowbird parasitism on the probability of brood reduction in the Brown-and-yellow Marshbird, a common host in the Argentinean Pampas. We used a nine-year database of nesting success of Brown-and-yellow Marshbirds. We compared the number of host fledglings produced and assessed the effect of year, parasitism (if the nest was parasitized or not); overall brood size (including cowbird and Brown-and-yellow Marshbird nestlings); and hatching delay (delay between the first hatched chick and the last one) over the probability of brood reduction. Parasitized and non-parasitized nests had a similar clutch size, but parasitized nest produced a lower number of Brown-and-yellow Marshbird fledglings. About 25 % of nests suffered brood reduction most of them were parasitized by cowbirds (68 %). Hatching delay was the main factor associated to brood reduction in this species. It was associated to number of cowbird eggs present in the nest and overall brood size. The results we obtained reinforce the idea that cowbird egg laying synchronization imposes additional costs to host as it increases the probability of host brood reduction.