EFFECTS OF MALE REMOVAL ON THE BEHAVIOR AND REPRODUCTIVE SUCCESS OF FEMALE EASTERN BLUEBIRDS SIALIA-SIALIS

We removed male Eastern Bluebirds Sialia sialis to examine the importa nce of male parental care and the behavioural responses of unaided fem ales to loss of male assistance. Unaided females fed young significant ly more than control females (females with male assistance) fed young, but young in experimental nests were fed significantly less frequentl y in total than young in control nests. Unaided females had significan tly lower nesting success (fledged at least one young) than control fe males. At control nests, males defended the young more strongly than d id their mates. Unaided females defended their young as strongly as co ntrol females. Unaided and control females spent the same amount of ti me brooding young, and there was no tradeoff between feeding and brood ing young. Most early season experimental nests failed, but late in th e season many unaided females were as successful as pairs. Unaided fem ales were able to match the feeding rate in control broods at late nes ts but not at early nests, where control nestlings were fed at a highe r rate. In our population, male bluebirds played an important role in provisioning young, and early in the season unaided females were unabl e to provide sufficient food to raise any young to fledging.