A male nightingale’s trills could help females determine his age, according to a study published last week (August 12) in the Journal of Avian Biology. The nightingales’ intricate warbling sounds, combined with other vocal features, help the birds advertise their suitability as mates.
Older male nightingales have been previously shown to have greater reproductive success than younger birds, and among territorial species, older individuals often excel at defending their territory.
To determine the purpose of the birds’ trilling, researchers obtained 19 wild nightingales from a nature park in France and recorded their bill shape, wing length, body mass adjusted for size, and age, as judged by their plumage. Upon releasing the birds, the researchers recorded their songs.
After comparing the quality of the birds’ trills—fast and repetitive vocal figures that take great effort to produce—the researchers performed statistical analyses to determine whether the sounds were predictive of the birds’ traits. They found that older males were able to produce more rapid trills with a higher frequency bandwidth than younger males. Males with narrow bills sang more consistent trills than broader billed individuals.
While trills could tell a female bird how old a suitor was, other elements of the nightingale’s song provide additional information. For instance, a low, narrow-band sound called a buzz has previously been shown to signal a nightingale’s body mass. “Indeed, nightingales may use the full spectrum of their song versatility to encode different information on signaler characteristics such as age, condition, and morphology, by using different song traits,” the authors wrote.