Nest sites and breeding success of Baywinged Cowbirds (Molothrus badius)

Abstract

Molothrus badius nested in a diversity of natural locations (foliage, cavities, palm trees, etc.) and in nest boxes in a study area in Argentina. No other local passerine showed such diversity of nest locations. Nests built by 3 other species of birds were used, but less frequently than holes. Nest piracy was rare. Some successful nest sites were used for 5–6 breeding seasons. Predation affected only 9 % of the nests. The timing of breeding was not earlier for females using nests built by other birds than for those nesting in other locations. The amount of nest building bybadius was similar for most nest sites. I found no significant differences in the incidence of brood parasitism byM. rufoaxillaris andM. bonariensis between different types of nests. Productivity of young forbadius was not higher for nests in structures built by other birds than for nests located elsewhere,