Distraction display
[16] 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.
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.
[1] 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,[18] perhaps through cultural transmission.
[21] 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.
[1] 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.
[14] There are several conditions in which distraction display may be advantageous to the animal, such that the incorporation of displacement or stress behaviors into offspring defense will most likely undergo positive selection.
[22][4] Ground-nesting birds employ different defensive behaviors as part of their antipredator strategies because they nest where a wide range of predators have access.
[13][25] Such injury-feigning displays are particularly well known in nesting waders and plovers, but also have been documented in other species, including snowy owls,[20] the alpine accentor,[25] and the mourning dove.
One hypothesis is that the display arose from a courtship behavior in which the male normally "points" an approaching female towards his nest so that she may lay her eggs within it.
When the nest was approached, the female attempted to lead the researcher away through the trees using a ventriloquistic call that resembled the cries of the young.
[12] An additional study documented distraction display in Mentawai langurs, whereby a male will call loudly and bounce on branches while the female and young are able to quietly hide.
[8] In addition, the presence of a second parent at the nest correlates with increased display intensity, perhaps representing a diluted predation risk.
[27] The number of potential extra-pair mobbers has also been shown to marginally increase the intensity of the display, again representing a possible dilution of risk to each of the animals engaging in the distraction.
[25] However, some studies[27] have failed to find any correlation between the cost of replacing a brood (a measure of parental investment) and the frequency of distraction display.
As such, distraction display may be a profitable strategy for the grouse in years following rodent population booms, as there is less risk of encountering a "smart" predator.
