Behavioural traits of a successful avian urban adapter, the noisy miner (Manorina melanocephala)

Increasing urbanization means that wildlife must adjust to this altered environment or be excluded from it. Most species appear to be unable to adjust to the high disturbance levels and changes to habitats and resources that accompany urbanization, but a few thrive in this evolutionarily novel environment. To date research on urban colonization by wildlife has focused largely on resource-based (i.e. food and habitat) limitations to colonization. By contrast, much less attention has been given to behavioural traits that might facilitate urban habitation. The current study focused on the behaviour of an avian urban adapter, the noisy miner, Manorina melanocephala. Firstly, I compared the response of urban and rural noisy miners to a startling sound stimulus (a loud noise). Secondly, several calls of this species were compared between urban and rural conspecifics. Finally, the amplitude of noisy miner alarm calls was compared between areas with contrasting background noise levels (arterial roads and residential streets) in the urban environment. Urban noisy miners were less ‘flighty’ and more aggressive than rural individuals in response to loud noise playback. Focal birds in both areas usually remained at the playback site and visually surveyed the area, suggesting that noisy miners are inherently quite bold (i.e. have a relatively high disturbance-tolerance). Although urban noisy miners exhibited a shift in the minimum frequency (kHz) of some call-types relative to rural individuals, it was not sufficient to preclude vocal masking from low level, background, anthropogenic noise. However, several call components of this species appear to be naturally suited to being heard in noisy urban environments (i.e. they have high dominant and maximum frequencies [kHz]). As an additional and/or alternate vocal modification, noisy miners also exhibited the Lombard effect, calling more loudly on noisy arterial roads than on quieter residential streets in urban Melbourne. Overall, the findings suggested that noisy miners are probably inherently well suited to inhabiting cities by virtue of having a relatively high disturbance-tolerance and calls with features that make them easy to detect in noisy environments. In addition, these birds appear to have the flexibility to adaptively modify their vocal behaviour through adjustments to the frequency (kHz) and amplitude of their calls in such a way as to retain broadcast efficiency in the noisy city environment.