Testosterone Linked to Song Behavior in Tropical Birds

Researchers have discovered that the female African white-browed sparrow weavers can sing the male-typical solo song via an increase in testosterone hormones.

Male songbirds living in a temperate zone are known to experience a rise in the concentration of sex hormones in spring. This causes the songbirds to increase their song activity during the breeding season.

Seasonal fluctuations also trigger circannual rhythms in male birds living in the temperate zone. Longer the days in spring, higher the steroid hormone levels, thus causing the breeding activities to begin. The behavior of the male songbirds also change, suggesting that there is a link between song activity and the testosterone concentrations.

Until now, experts have not been able to find evidence of a relationship between song activity and hormone levels in birds living in the tropical zone due to lower degree of seasonal changes in the environment. Tropical birds indulge in song activity all year-around and many species have low testosterone levels throughout the year. It remained a mystery as to what caused song changes in birds living in tropical zones.

But now a team of researchers from the Max Planck Institute for Ornithology in Seewiesen has found evidence showing that the song behavior of dominant African white-browed sparrow weavers living in tropics is linked to higher levels of testosterone.

These birds live in groups of two to 12 individuals and they are differentiated by a status-dependent song. While the dominant male birds are known to sing a solo song, other males and the female birds sing an alternative duet song.

Researchers studied the sparrow weaver colonies in southwestern Zimbabwe and found that the dominant males have higher testosterone values than the subordinate ones during the early (from October until December) and late breeding season (from January until March).

But the hormone levels were much lower compared to those in songbirds living in temperate zones. It could have been possible that the higher testosterone values might be reflecting their dominant status and have nothing to do with the changes in song behavior.

In order to confirm that the testosterone levels are responsible for song activity, experts tested the female birds by giving them a testosterone implant. The birds were receptive to the male hormone testosterone and started singing the male-typical solo song within a week with differences only in some aspects as compared to the male song.

The study showed evidence that the male song can be activated by testosterone in both the sexes.