Double Brooding by the Northern Wheatear on Baffin Island
Most Arctic-breeding passerines raise a single brood in a season, presumably because the short Arctic summer does not provide sufficient time to raise a second brood. Here we document the first cases of two broods being raised or attempted, after successful fledging of a first brood, in an Arctic-breeding population of Northern Wheatears Oenanthe oenanthe, at Iqaluit, Nunavut, Canada, in 2010 and 2011. In one case, the same pair was involved in raising both broods. In a second case, the female that raised the first brood was mated to a different male for her second brood. In a third case, it was not known whether the same male was involved in a female’s attempts to raise two broods. The three females that attempted to raise two broods started their first clutches four to six days earlier than the estimated median date of laying first eggs and represented about 6% of all females in the study population. Potential constraints on raising two broods include not only the shortness of the summer season but also the nature and abundance of the food supply, trade-offs between the success of the first brood and that of the second brood, and effects of the one- and two-brood strategies on the survival and future reproductive output of the adults.