Nesting jackdaws’ responses to human voices vary with local disturbance levels and the gender of the speaker

Abstract

The ability to detect and respond to indicators of risk is vital for any animal and, for many species, humans represent a key threat. We investigated whether wild jackdaws, Corvus monedula , a species that thrives in anthropogenic environments but is regularly persecuted by people, associate human voices with differential degrees of risk and differ in their responses according to local levels of human disturbance. Playbacks showed that nesting females did not discriminate between the voices of familiar men who posed differing levels of threat, generalize to unfamiliar individuals with similar regional accents or discriminate between familiar and unfamiliar accents and voices. They were, however, considerably more wary towards male than female human voices, which may reflect the greater likelihood of negative experiences with men than women. Responses to playbacks also differed across fine-scale spatial locations: females nesting in areas of the colony with high levels of disturbance were less likely to leave the nest cup in response to playbacks and were more wary on their return to the nest than birds nesting in less disturbed areas. Nevertheless, levels of local disturbance did not influence reproductive success. Together these results indicate that, although vocal cues alone may not suffice for wild jackdaws to discriminate between individual humans or generalize across categories of people, sensitivity to cues of gender and local disturbance may help jackdaws to optimize their defensive behaviour and maintain breeding success. Further research into plastic responses towards indicators of human risk is vital to understand and mitigate the impacts of increasing urbanization on wildlife populations. • Nesting jackdaws were more fearful of playbacks of men's than women's voices. • No discrimination based on voices' accent, familiarity or threat level was found. • Birds used to high disturbance were less likely to inspect or flee voices. • Birds were warier when returning to nests in areas with high levels of disturbance.