Effects of female pairing status and timing of breeding on nesting productivity in western meadowlarks (Sturnella neglecta)

Abstract

The nesting ecology of western meadowlarks (Sturnella neglecta) in southern Manitoba is strongly influenced by the timing of breeding. Physical characteristics of nests change, apparently in response to seasonally altered thermal demands. The largest eggs and the largest clutches are produced in the middle portion of the breeding season, and nests initiated at that time produce the greatest number of young. Nevertheless, nesting productivity is highest for females that begin nesting earlier in the season and that can therefore renest if their initial attempt fails. Females breeding with already-mated males have, on average, as high a reproductive success as do primary females. Nevertheless, nestlings of secondary females frequently starve if they do not receive a male's parental care. Asynchronous hatching and facultative brood reduction may decrease the total losses incurred through nestling starvation, and may be adaptations that allow successful polygyny in this species. Aggressive interactions between resident and unmated females may protect a primary female's "preferred" status and may affect a male's ability to breed bigamously.