Effect of predation and cowbird parasitism on the nesting success of two sympatric Neotropical marshbirds.

FERNÁNDEZ, G. J..; MERMOZ, M. E.

WILSON BULLETIN

Año: 2000 vol. 112 p. 355 - 365

0043-5643

We compared the effect of nest predation and cowbird parasitism on the breeding success oftwo simultaneously nesting ecologically similar blackbird species that differ in their breeding strategies. TheScarlet-headed Blackbird (Amblyramphus holosericeus) is a monogamous species that performs territorial defense.In contrast, the Brown-and-yellow Marshbird (Pseudoleistes virescens) is a non-territorial monogamousbreeder that performs mate guarding and has helpers at the nest. Both species suffered similar nest predationrates throughout their nesting cycle. However, the Brown-and-yellow Marshbird suffered higher parasitism fromShiny (Molothrus bonariensis) and Screaming cowbirds (M. rufoaxillaris) than the Scarlet-headed Blackbird(62.6% vs 15.4%). Brood parasitism accounted for most of the egg losses and hatching failures in Brown-andyellowMarshbird. Parasitized nests had lower egg survival and hatching success than non-parasitized ones.Mean clutch size was 1.5 eggs larger in Brown-and-yellow Marshbird than in Scarlet-headed Blackbird. However,Scarlet-headed Blackbird had higher hatching success than Brown-and-yellow Marshbird and similar fledgingsuccess. Consequently, both species produced similar numbers of fledglings. We did not detect any relationshipbetween the reproductive success of these species and their breeding strategies. The presence of helpers atBrown-and-yellow Marshbird nests did not affect nest defense or chick survival, but helpers might account forreduced parental effort by supplementing food delivery to chicks/fledglings