Vocal signals are important in territoriality and mate attraction across animal taxa. Vocalizations are particularly elaborate in some groups, such as songbirds, which learn their songs, but much remains to be known about the physiological mechanisms that produce variation, especially in vocalizations of nonlearners. We address the extent that androgen treatment of female and juvenile golden-collared manakins, Manacus vitellinus, activate the male-like ‘chee-poo’ vocalization to determine (1) the extent that the vocal circuitry is developed and sensitive to androgens in females and (2) to identify the characteristics, including finer acoustic features, of vocal behaviour that are influenced by androgens in females and young males. We analysed recordings of nonbreeding females and juvenile males given implants containing testosterone (T) or blank implants during a period of 3 weeks in an outdoor aviary in Panama. T-treated females, but not control females, produced chee-poos, and their vocalizations showed consistent differences in acoustic features from those of males. This indicates that the neuromuscular systems are well developed or relatively rapidly developed in response to T administration in females. Both T-treated and control juvenile males produced chee-poos, although vocal production was higher in the treatment group. Surprisingly, T treatment of juvenile males resulted in chee-poos with increased acoustic similarity to those of females, such as increased duration and frequency bandwidth. These features may indicate an important role for chee-poos in aggressive interactions. Future work will address the contributions of central and peripheral components in vocal variation in golden-collared manakins.
