Passerine reactions to human behaviour and vegetation structure in Peterborough, Canada

Different bird species react differently to human proximity in urban parks. The ‘alert distance’, i.e. the distance between a bird and an approaching person when the bird reacts visibly to the intruder, and the flight distance, the distance between the two when the bird takes flight, vary for different bird species. Such alert distances are less studied for passerines. This paper examines the alert and flight distances of ten variably sized passerine species in Peterborough, Ontario, Canada. Subject birds were approached by an observer walking at a constant speed, using frontal and sideways approaches and either immobile or swinging arms, to test the hypothesis that alert distances vary according to human movements, bird size, and surrounding vegetation. All species recorded longer alert distances when the approaching person used a frontal, rather than a sideways approach, and also recorded longer alert and flight distances when the person used arm movements, as against walking with no arm movements. Apart from human arm movements, the strongest positive predictor of alert distances was bird size, while significant negative predictors were tree and shrub height and vegetation cover. Contrary to some other studies, increased vegetation height and cover more often reduced than increased alert distances, and open grass did not increase alert distances. Path and road proximity was not a significant predictor of alert distance. If sensitive to such issues, park design may include more trees and shrubbery, balancing conservation with human recreation and security concerns.