Similar nest defence strategies within pairs increase reproductive success in the eastern bluebird, Sialia sialis

Recent research suggests that individuals across a variety of taxa express consistent behavioural differences, or personality, which may affect reproductive success. Most previous studies of avian systems investigated the effects of individual personality on offspring recruitment and other fitness correlates, even in species with biparental care. Here we tested the potential for behavioural similarity within mated pairs of wild eastern bluebirds to impact reproductive success. Specifically, we quantified nest defence behaviour of males and females to address three hypotheses: (1) the individual personality hypothesis, which predicts that individuals with more aggressive personalities will have more nestlings survive to fledging; (2) the pair coordination hypothesis, which predicts similarly behaving pairs will have more nestlings survive to fledging; and (3) the pair intensity hypothesis, which predicts pairs with more aggressive personalities will have more nestlings survive to fledging. Pairs that had similar nest defence strategies produced more fledglings in support of the pair coordination hypothesis. We found no support for either the individual personality hypothesis or the pair intensity hypothesis. Thus, particularly in species with biparental care, it is important to consider the behaviour of both pair members to predict effects on reproductive success.