Seasonal Hormone Fluctuations and Song Structure of Birds

Abstract

Traditionally, it is assumed that singing of birds is a male-typical testosterone-dependent behavior. In this review I point out that singing outside the breeding season is common in males of many songbird species while their testosterone levels are low. Further, females of many tropical and temperate songbird species sing in various context in- or outside of the breeding season but testosterone levels of singing females are low in most cases. These findings question the testosterone-hypothesis of song production of songbirds. However, a key problem is the interpretation of “high” versus “low” testosterone levels, which would require a basic understanding of the quantitative interaction of testosterone and its estrogenic derivate with their specific receptors, as well as the dynamic abundance of these receptors in song controlling systems.