Androgen-armoured amazons – reversed sex roles in coucals are associated with testosterone in females but not males

In some species, sexual selection is stronger in females than males. In classically polyandrous birds, for instance, females compete for mating opportunities and males care for offspring. Sex steroids such as testosterone have been suggested to regulate the behaviours of ‘role-reversed’ females and males, but comparative studies did not find evidence for a role of testosterone in relation to sex roles. However, the large variability of hormone measurements across laboratories may prevent detecting subtle differences in hormone levels. To circumvent this caveat, I compared sex steroid concentrations of females and males of two closely related and cohabiting species with different mating systems, the classically polyandrous black coucal (Centropus grillii) and the monogamous white-browed coucal (C. superciliosus). Baseline and GnRH-induced testosterone concentrations  were twice as high in female black coucals than  female white-browed coucals, and the low pre-breeding progesterone concen..., For details on the methodology see main manuscript,