Tolerance of human approaches by Common Mynas along an urban-rural gradient

Successful urban colonisation by birds requires tolerance of many disturbances and avoidance of chronic stress and major disruption to critical activities. Habituation may be involved in acquiring tolerance of human proximity, in which case tolerance should vary with the degree of opportunity to learn that most humans do not present a threat and should therefore vary with human population density. We studied Common Mynas (Acridotheres tristis) in the urban, suburban, peri-urban and surrounding rural zones of Melbourne, Australia, to determine whether flight-initiation distance (FID) and time allocated to anti-predator vigilance increased along this gradient from the urban to the rural zone. This gradient encompassed a 143-fold variation in average human population density during daylight hours. Urban and suburban Mynas had a 2.3-5.7 times shorter FID, were 1.6-2.5 times less likely to retreat by flying and were 1.9-3.1 times more likely to flee >5m than their peri-urban and rural conspecifics. Fleeing behaviour was not strongly correlated with estimated human population density, but exhibited an apparent 'step' in response at the suburban-peri-urban divide. Vigilance effort did not vary significantly between zones. This suggested that habituation did not occur with respect to surveillance for people, although surveillance presumably encompassed other predators too. Similar foraging effort and rates of food acquisition among zones could suggest that food abundance per individual was similar in urban and rural environments for Common Mynas, although this requires direct measurement.