by Thomas Fernandes

Like the Thomson’s gazelle of Part I, the white-tailed deer (Odocoileus virginianus) evolved an ability to communicate with predators. Not by stotting but by flagging the white underside of their tail.
Why is this considered communication? Communication requires intention, distinguishing a cue from a signal. To a deer, a predator’s smell coming from upwind is a cue. By marking their territory, deer leave signals to others. Cues emerge from simple correlation, association of one signal (odor) with another (the presence of a predator). Over evolutionary time, cues can become signals. After detecting a predator, a deer might turn to flee. Predators constantly evaluate whether to pursue a chase, paying close attention to cues of early detection and fitness. Once predators use these cues to abort the chase, deer might evolve increasingly conspicuous displays, like flagging a highly contrasted tail, simply to advertise this cue to the predator. At this point, the fleeting readiness cue evolves into a fleeting readiness signal.
To be relevant the signal should not be only about detection but also about the ability to outrun predators. As predicted, faster deer are observed to be more likely to wag their tails and the proportion of time the tail stands erect increases with flight speed (Caro et al., 1995). While it may seem surprising that slower deer would not try to bluff their way out of a hunt, a signal is only as efficient as it is honest. If tail wagging were used every time regardless of flight capabilities, it would make the signal meaningless. After all, signals are built from correlations that are of interest to both the sender and the receiver. Break the correlation, break the signal, and everybody loses.
To better understand this behavior, a comparison with mule deer (Odocoileus hemionus) proves insightful. Read more »







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