Hatching asynchrony in the house wren, Troglodytes aedon: A test of the brood-reduction hypothesis

We tested the brood-reduction hypothesis by adding three nestlings to naturally occurring synchronous and asynchronous broods of the house wren (Troglodytes aedon) in order to mimic food shortages for the broods. Two types of controls were established in which brood size remained unchanged: those in which nestlings were exchanged among broods and those in which no nestlings were exchanged. The critical test of the hypothesis was in 1988 when there was a food shortage for enlarged broods. Although brood reduction occurred, enlarged synchronous broods produced as many fledglings as did enlarged asynchronous broods, and fledging mass was similar. Juvenile recapture 2-8 weeks after fledging and offspring recruitment to subsequent breeding populations were not related to treatment. The results are not consistent with the brood-reduction hypothesis as an explanation for the occurrence of hatching asynchrony in the house wren.