The higher on the social ladder, the bigger the brain. At least for white-browed sparrow weavers. These African songbirds live in groups where only one male and female pair mate, and according to a new study, the lucky male has the largest brain because of his status. Another reason his subordinates are… subordinate.
The notes, ranges, and melodies of songbirds are impressive, so it’s not a surprise that a large part of a songbird’s forebrain is dedicated to both learning and singing songs. In many bird species, where only the males do the singing, this song production center is much larger in the males than in the females. Yet in species where both the males and the females do the singing, the song centers of the sexes are closer in size.
Based on these observations, researchers thought that the song behavior of the guys and gals was dependent on brain size. But researchers from the Max Planck Institute for Ornithology in Seewiesen, Germany, who studied the white-browed sparrow weavers (video), found something different: even though both sexes sing the same song, the male still had the bigger brain. The scientists think it has to do with rank, and published their results in PLoS ONE.
The sparrow weavers live in small groups of two to ten birds, and although all the birds perform beautiful duets with a partner, only one male and female mate. Besides his unique opportunity for love, the dominant male also stands out from the crowd because he has a special song that he lets loose at dawn. None of the other males get to sing this song. When the scientists compared the size of the song centers between dominant and subordinate males, they found that the dominant males definitely have bigger brains. However, when they looked at the brain sizes of the subordinate males and the dominant females, who sing the same amount, the brain of the subordinate male was still larger than the dominant female’s, by almost 2 times.
The male may still have the bigger bird brain because all males have the potential to be dominant. This means that all the males still learn the solo song when they are growing up, but are kept silent by the dominant male.
The dominant males also have to have a good ear. The head honchos of neighboring groups of sparrow weavers will sing at the same time and some researchers have witnessed ‘song matching,’ which is when one bird changes his own song to reflect what the other is singing. The escalating singing battles may be a sign of aggression between the groups and another reason why the dominant male’s brain is larger: to make sure he doesn’t embarrass himself by being off pitch.
White-browed sparrow weaver nests (picture)