Social polygyny in the Eastern Bluebird (Sialia sialis)

Abstract

I recorded social polygyny in an Eastern Bluebird (Sialia sialis) population located in central Wisconsin. A male simultaneously tended nests with 2 different females at his second and third broods. The polygyny threshold model is not an adequate explanation of this observation. Polyterritoriality cannot be ruled out. Multiple brooding behavior likely created an opportunity for an early breeding male to exhibit social polygyny. Food supplements and breeding asynchrony likely mitigated the costs of sharing a male.