Animals living in the wild are frequently subject to frightening events, including being hunted or injured by predators. This can impact their behavior, including how strongly they react to alarming stimuli, how much they eat, and how successfully they raise offspring after the frightening event. Recently, researchers from Western University, London in Ontario, Canada reviewed studies of how animals react to predator encounters and how this in turn impacts their ecosystem.

This review found that when an animal is afraid because of the presence of a predator, that animal will tend to eat less after the encounter. The effect is even larger if the animal is physically injured by the encounter. This was true in a variety of different animals, including songbirds, small mammals like mice and arctic squirrels, and larger mammals like deer and impala. In many animals, eating less means they later on gave birth or laid eggs less often, and fewer of the resulting young survived to adulthood. However, because they spent more time hiding rather than foraging, adult animals survived longer before being caught by a predator, giving them more opportunities to attempt to raise young.

Several of the reviewed studies also monitored changes in the brains of animals stressed by predators. Even long after the stressful event, these animals often showed increased stress hormones and more behavior indicating alertness to potential danger. There was also a decrease in new neurons forming in the parts of the brain that control fear, similar to the neurological changes seen in humans experiencing post-traumatic stress disorder, or PTSD. Further studies could examine the effects of fear in more animal species and in how these experiences can elucidate the effects of stressful experiences on humans.

First author Liana Y. Zanette is a professor at Western University studying the ecological effects of fear of predators.

Managing Correspondent: Emily Kerr

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Image Credit: NPS/Patrick Myers