Distraction display

Distraction displays, also known as diversionary displays, or paratrepsis are anti-predator behaviors used to attract the attention of an enemy away from something, typically the nest or young, that is being protected by a parent. Distraction displays are sometimes classified more generically under "nest protection behaviors" along with aggressive displays such as mobbing. These displays have been studied most extensively in bird species, but also have been documented in populations of stickleback fish and in some mammal species.

Distraction displays frequently take the form of injury-feigning. However, animals may also imitate the behavior of a small rodent or alternative prey item for the predator; imitate young or nesting behaviors such as brooding (to cause confusion as to the true location of the nest), mimic foraging behaviors away from the nest, or simply draw attention to oneself.

The behaviour was first described by Aristotle in his History of Animals.

David Lack postulated that distraction displays simply resulted from the bird's alarm at having been flushed from the nest and had no decoy purpose. He noted a case in the European nightjar, when a bird led him around the nest several times but made no attempt to lure him away. He additionally noted courtship displays mixed with the distraction displays of the bird, suggesting that distraction display is not a purposeful action unto itself, and observed that the display became less vigorous the more frequently he visited the nest, as would be expected if the display were a response driven by fear and surprise.

Other researchers, including Edward Allworthy Armstrong, have taken issue with these arguments.^[when?] While Armstrong acknowledged that displaying animals could make mistakes, as Lack's nightjar seems to have done in leading him around the nest, he attributed such mistakes not to paralytic fear but to a conflict of interest between self-preservation and reproductive or enemy attack impulses: the bird at once experiences a drive to lure the predator away and also to directly guard the young. Armstrong also thought that the incorporation of sexual and threat displays into the distraction display did not necessarily represent a mistake on the part of the animal, but "might make the display more effective by increasing its conspicuousness". Finally, the observation of less vigorous displays due to repeated nest approaches does not preclude the parent animal simply learning that the human is not a threat to its young. Jeffrey Walters provided evidence that lapwings possessed the ability to distinguish between different types of predators of varying threat levels, a behavior which is presumably learned, perhaps through cultural transmission.

Armstrong additionally noted that displaying animals were rarely captured by predators, as would be expected if the display were truly uncontrolled, and that the movements seemed to show signs of some sort of control by the animal, although likely not conscious, intelligent control. One example of apparent control is attention seemingly paid to routes used by the displaying animal when moving away from the nest. Furthermore, researchers have noted parent animals moving towards the predator during the display. While some of these cases could be attributed to mistakes made during "partial paralysis", in the case described by Wiklund and Stigh, snowy owls consistently walked or ran towards the predator while displaying, suggesting that the action was deliberate.

An additional hypothesis in alignment with Armstrong's ideas about conflicting impulses suggests that the incorporation of sexual and threat displays into the distraction display may represent displacement. Displacement occurs when an animal, unable to satisfy two conflicting impulses, may initiate an out-of-context behavior to "vent". If a displacement behavior served an adaptive function, such as increased survival of the young, then it may have experienced positive selection and become ritualized and stereotyped in its new context.

In any case, there are some forms of distraction display which may in fact have evolved from stress responses, an idea more in alignment with Lack's hypothesis. One of these is the "rodent-run" display, in which a bird fluffs its feathers to mimic the fur of a rodent and scurries away from the nest. It is possible that this display originates from a feather ruffling reflex to alarm.