Alert distance as an alternative measure of bird tolerance to human disturbance: implications for park design

Animal tolerance to human approaches may be used to establish buffers for w ildlife that can minimize the probability that animals will be disturbed by human activity. Alert distance (the distance between an animal and an appr oaching human at which point the animal begins to exhibit alert behaviours to the human) has been proposed as an indicator of tolerance mainly for wat erbirds; however, little is known about its utility for other bird species. The factors that influenced alert distances of four bird species to pedest rian approaches in five large wooded fragments in the city of Madrid (Spain ) were analysed. Location of human activity affected only Passer domesticus alert distances, which increased in the proximity of pathways. Habitat str ucture modified alert distances of all the species (Passer domesticus, Turd us merula, Columba palumbus, and Pica pica), increasing bird tolerance with greater availability of escape cover (shrub and coniferous cover, and shru b height). Alert distances varied among species, with large species being l ess tolerant of human disturbance than small ones. Alert distance appears t o be a more conservative indicator of tolerance than flight distances, beca use it includes a buffer zone (the difference between alert and flight dist ance) in which birds may adapt their reaction to the behaviour of visitors. Alert distance may be used in the determination of minimum approaching are as, allowing people to enjoy their visit to parks, and birds to use patches for foraging and breeding without being displaced.