For decades, birdsong research focused almost exclusively on males. In many species, however, females also sing. Now a study by researchers from the University of Vienna and Anglia Ruskin University shows that female Galápagos yellow warblers sing frequently, though not for the reasons males do. In experiments simulating territorial intrusions, the researchers found that female song was neither linked to same sex competition nor to signalling aggression in territorial defence. The findings, published in the journal Animal Behaviour, raises new questions for the function of birdsong.
Birdsong has been studied for decades to understand the evolution of vocal communication. Yet female song was largely overlooked: partly because females were long assumed to play only a passive role in sexual selection and partly because research focused mainly on Northern Hemisphere species, in which males typically sing more frequently than females.
Recent studies – building on two decades of growing research on female birdsong – suggest that female song is far more widespread than previously assumed and occurs in more than half of songbird species, particularly around the tropics. However, the function of female song remains poorly understood. Do females use song in the same way as males – for example in territorial defence, especially in competition with same sex rivals?
About the study
The research team studied Galápagos yellow warblers (
Setophaga petechia aureola) on Floreana Island in the Galápagos archipelago. During a field expedition in 2023, the researchers heard an unfamiliar song that had not been described in previous studies or field guides. The source turned out to be a female bird. To investigate the function of female song, the team conducted playback experiments simulating territorial intrusions. Songs of males, females and duetting pairs were broadcast to resident birds during both breeding and non-breeding seasons. The researchers looked for aggressive behaviour, recorded singing responses and also monitored territories across multiple years to examine whether song or aggression predicted territory retention.
Testing common explanations for bird song
Two common hypotheses about the function of male song were tested for female song. One possibility was that females use song in intrasexual competition, for example to signal aggression toward other females. Alternatively, female song could function in territorial defence, guarding resources against intruders of either sex. However, the data supported neither hypothesis. Female song occurred mainly in the non-breeding season. During this period, females showed strong aggressive responses to simulated intruders. They also produced songs and participated in vocal interactions. However, singing was not associated with aggressive behaviour. "Male song was closely linked to aggression during territorial encounters," explains first author Alper Yelimlieş from the Department of Behavioral and Cognitive Biology at the University of Vienna. "In females, however, singing and aggression appeared to be unrelated behaviours." Another striking pattern was that females rarely sang alone. Instead, most of their vocalizations occurred as duets with their partners, typically initiated by the male.
Singing together: communication within the pair
Because female song did not function as an aggressive signal, the researchers suggest that it may instead play a role in communication between partners. "Most female songs occurred as duets with their paired mates, suggesting that they may function in communication within the pair rather than as a territorial signal," says Yelimlieş. "Studying female song is therefore essential for a complete understanding of how vocal communication evolves in birds." By documenting female song in Galápagos yellow warblers, the study adds new evidence to recent efforts to address long-standing biases in behavioural biology.
Summary
- Female birdsong has historically been underrepresented in behavioural research
- Researchers documented frequent female singing in Galápagos yellow warblers
- Females sang mainly during the non-breeding season and primarily in duets with their partners
- Female song was not linked to aggressive territorial behaviour
- The study found support for neither the territorial defence nor the intrasexual competition hypothesis