Data from: Why do females sing? Pair communication and other song functions in eastern bluebirds.

Female bird song has been underappreciated and understudied, especially in
temperate species. Birdsong was originally thought to be a trait used
primarily by male songbirds for mate attraction and male/male contest.
However, ornithologists have long known that females sing in many tropical
songbirds, often for similar functions to male song. Yet studies of female
song in temperate regions remain scarce. Increasing our understanding of
the function of female song in temperate species is a powerful step
towards discerning the selective pressures that maintain elaborate female
signals. In the last few decades, studies of temperate species have
highlighted five major functional categories of female song. Using a
modelling framework, based on all known functions of song in other
species, we tested the function of female song in eastern bluebirds. The
modelling framework allowed us to test the effect of multiple complex
behaviors simultaneously to predict female song function. Additionally,
modelling mitigated issues of multiple testing across the five different
functional categories. We found that female song in eastern bluebirds is
primarily used in pair communication. Specifically, females sing to
strengthen and maintain long-term pair bonds. Strengthening pair-bonds may
be advantageous for eastern bluebirds as pairs that remain together
between nesting attempts and between years have higher reproductive
success. We demonstrate a clear link between the function of female song
in pair communication and the likely selective force of long-term pair
bonds acting on eastern bluebird reproductive success. Additionally, our
study highlights a major function of female song in a temperate species.