May 08 2014
Brown-headed cowbirds are courting now because their victims are about to nest. The males sing a bubbly whistling song to attract a favored female. After she’s chosen a mate, Mrs. Cowbird lays her eggs in the nests of smaller birds whose own eggs and nestlings die while the foster cowbird chick thrives.
In cowbird society nest building and incubation never occur so the pair bond is cemented by courtship songs and postures. Amazingly, the quality of the male’s song really matters. That’s how the female decides who to accept and who to ignore.
What happens if a female can’t tell the difference between good and bad songs? What happens when one lady in the flock doesn’t follow the rules? Last year scientists learned that one tone-deaf female can upset cowbird society.
Researchers at the University of Pennsylvania led by Sarah Maguire inactivated the song-control centers of some female cowbirds’ brains so they could no longer distinguish between high and low quality songs. When placed in a mixed-sex flock these ladies reacted to all songs and did not stay with a chosen male for long.
Since male dominance among cowbirds is based on song quality the best guys usually get the best gals. However, when a tone-deaf female appeared in the flock she listened to all males equally and the minor males got a boost. The dominant males courted the altered female more vigorously. The other ladies were left in the cold.
Which guy will she choose? One tone-deaf female can mess up an entire social structure.
Read more here in PLOS One.
(photo from Wikimedia Commons, Creative Commons license. Click on the image to see the original)