Escape distance

The escape distance (ED) of animals is the distance within which an animal will, upon observing a disturbing stimulus such as a human, exhibit an escape response, such as flushing (in the sense of being "flushed out") in the case of birds. More specifically, it is the upper bound of the set of distances within which the animal is certain to exhibit such a response should it observe the stimulus. It may also be termed flight initiation distance (FID), flush distance, or escape flight distance. The alert distance (AD) is the distance, by definition greater, within which the animal changes its behaviour in a manner enabling it to better observe the stimulus, as by raising the head in an alert posture, but does not necessarily flee unless the stimulus is also within the escape distance. These measures are usually used to quantify the tolerance of wildlife to humans.