Constraints on Double Brooding in a Neotropical Migrant, the Hooded Warbler

We examined the constraints on double brooding in Hooded Warblers (Wilsonia citrina) to explain why 56% of females with successful first nests did not attempt second broods. Double brooded females fledged on average 1.9 more young than single brooded females. Double brooded females nested significantly earlier than single brooded females, but many females with early nests did not double brood. There were no significant differences among single and double brooded females in age, experience, body condition, or reproductive output at their first nest. Female breeding strategy did not depend on male age or male feeding effort at the first nest. Double brooded individuals were usually feeding fledglings while undergoing their pre-basic molt, and the main cost of being double brooded was a three week delay in molt compared with single brooded birds. This delay in molt could impose a high energetic cost due to the overlap of molt and fledgling care, and a time cost in terms of delaying migration and the acquisition of a winter territory.