Female bluebirds sing to strengthen and maintain the bond with their mates.
Why Do Female Birds Sing?
Why do birds sing in the morning? - Australian Geographic
Vocal communication
Female aggressive response and hormonal correlates—an intrusion
Female Birds Sing, Too - Edge Effects
Why Do Birds Sing the Same Song Over and Over?
Female Birdsong Is Finally Getting the Attention It Deserves
Duets recorded in the wild reveal that interindividually coordinated motor control enables cooperative behavior
fairy-wren Archives - Australian Geographic