||It has been suggested that this article be merged into Flight zone. (Discuss) Proposed since April 2013.|
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.
The area surrounding the animal which will cause escape behavior when encroached upon is called the flight zone.
Wildlife managers often use ED and FID to develop set-back distances to reduce human impacts on wildlife,  both in wildlife refuges, and, e.g., in planning areas for outdoor recreation.
While escape distance has been generally used as a measure of tolerance, other changes in animal behavior in presence of humans, such as increased vigilance time at the cost of decreased feeding time, may have significant overall impact on wildlife. Therefore it is suggested that a more conservative measure, namely, the alert distance, should be used in determining minimum approaching distance. The latter typically adds a certain buffer distance to the given tolerance measure.
Sample escape distances (mostly mean) from humans:
Birds of Europe
|Brant goose Branta bernicla||(130-1000) 319|||
|Pintail Anas acuta||(100-500) 294|||
|Grey heron Ardea cinerea||255|||
|Mallard Anas platyrhynchos||(60-400) 236|||
|Lapwing Vanellus vanellus||162|||
|Dunlin Calidris alpina||(15-450) 70|||
|Coot Fulica atra||68|||
|Whinchat Saxicola rubetra||20-30|||
|Blackbird Turdus merula||10|||
|Blue tit Cyanistes caeruleus||10|||
Birds of North America 
Factors affecting escape distances for birds
Escape distance may differ significantly depending on many circumstances.
- Species  - for example mallard Anas platyrhynchos has shorter ED than pintail Anas acuta.
- Age - young birds are less shy, for example dunlin Calidris alpina)
- Location or rather habituation to walking people.  Mallards Anas platyrhynchos or Canada Geese Branta canadensis are less shy in a park than somewhere in the wild. Or Tits and Nuthatches near the feeder or in the park are less shy than in the wild.
- Season. For example wintering bullfinches Pyrrhula pyrrhula have shorter EDs than breeding ones. 
- Origin of birds - sometimes wintering birds from the north, perhaps not knowing people, are less shy than native, for example nutcracker Nucifraga caryocatactes 
- Given bird individual
- Color of clothes of an observer and observer's behaviour 
- Hunting status - quarry species have longer EDs than non-quarry, increasing during hunting season or after days with hunting. 
- Flock size 
- Flock composition - for example birds in mixed flocks of mallard Anas platyrhynchos and teal Anas crecca react at longer distances than those in single species flocks for either species.  Or dunlin Calidris alpina in flocks with other waders. 
- Visibility of the stimulus to the birds
- Wind force 
- Vegetation height 
- Fight-or-flight response
- Flight zone
- Nature photography
- Personal space
- Wildlife photography
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