Changes in fear responses of urban birds

Wildlife will often modify their behaviour when disturbed by humans. The distance at which animals flee from humans (flight initiation distance (FID)) generally decreases along the rural-urban gradient and as a function of time since the species’ colonisation. However, no known studies have monitored the ongoing responses of birds to urbanisation. To see how urban birds have responded to increasing urbanisation and how this varied between sites, I undertook an FID study at sites where FID had been measured in 2000. I examined how FID, response intensity (proportion of birds that walked away), and delays in flight after detecting the walker differed between the two periods, focusing on four species with the most observations. I found that in 2018, silver gulls (Chroicocephalus novaehollandiae) had significantly reduced FID both overall, and at the high disturbance sites, although there was no difference in response intensity. As expected, silver gulls and the Australian white ibis (Threskiornis molucca) also generally delayed flight more after detecting the walker in 2018 than in 2000. While species’ responses in the intervening years are unknown, these results suggest that these two species are responding to increasing urbanisation presence, while the masked lapwing (Vanellus miles) and pied oystercatcher (Haematopus longirostris) are not. The exploiter species (silver gulls and the Australian white ibis) were frequently encountered in situations where human-sourced food was available, and hence delaying flight would often have been beneficial, while it was less advantageous for the other two species to delay flight as they were generally utilising natural resources.