One of the most dramatic forms of antipredator activity is the alarm call given when a predator is sighted. For example, researchers have found evidence that vervet monkeys make very distinct and different calls in response to leopard, snake, and eagle predators. Vervets run to the trees when they hear a leopard alarm call, or they hide in bushes when a fellow vervet utters an eagle alarm call, suggesting that these monkeys are using alarm calls to indicate the mode of predator attack.
Belding's ground squirrels also give alarm calls when a terrestrial predator is sighted, but in this species, females are much more likely to emit such calls than males. The reason for this is tied to the demography and genetics of Belding's ground squirrels. Male Belding's ground squirrels move to new populations when they mature, but female squirrels spend their entire lives in their population of birth. This difference in dispersal creates an asymmetry in the way that adult males and females are related to others living in their populations. By remaining in the populations in which they were born, females (both young and old) are always surrounded by blood relatives. Mature males, who emigrate to new populations, however, find themselves interacting with complete strangers. By giving alarm calls, females get indirect benefits, in that they help protect their blood kin - males receive no such benefits, and call at much reduced rates.
Alarm calls need not be vocal. In ungulates, individuals are known to 'flag' their tails after a predator has been sighted. Such flagging occurs as part of a sequence of antipredator behaviors, and often involves an individual lifting its tail and 'flashing' a conspicuous white rump patch. Flagging often, but not always, occurs when a predator is at a relatively safe distance from its potential prey. This behavior has been postulated to (1) warn conspecifics (kin and nonkin) of potential dangers, (2) 'close ranks' and tighten group cohesion, (3) announce to the predator that it has been sighted and should therefore abandon any attack, (4) entice the predator to attack from a distance that is likely to result in an aborted attempt, and (5) cause other group members to flee, thereby confusing the predator, and making the flagger itself less likely to be the victim of an attack.
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