For Knowable Magazine, Sharon Levy investigated the possibility of post-traumatic stress in the animal kingdom.
Every few years, snowshoe hare numbers in the Canadian Yukon climb to a peak. As hare populations increase, so do those of their predators: lynx and coyotes. Then the hare population plummets and predators start to die off. The cycle is a famous phenomenon among ecologists and has been studied since the 1920s.
In recent years, though, researchers have come to a startling conclusion: Hare numbers fall from their peak not just because predators eat too many of them. There’s another factor, too: Chronic stress from living surrounded by killers causes mother hares to eat less food and bear fewer babies. The trauma of living through repeated predator chases triggers lasting changes in brain chemistry that parallel those seen in the brains of traumatized people. Those changes keep the hares from reproducing at normal levels, even after their predators have died off.
Two behavioural ecologists from the University of Western Ontario study “the ecology of fear” and found that a fear of predators led to some animals having less offspring. They wrote about this in a 2020 paper called Ecology and Neurobiology of Fear in Free-Living Wildlife:
[…] We review new experiments demonstrating that fear itself is powerful enough to affect the population growth rate in free-living wild birds and mammals, and fear of large carnivores—or the human super predator—can cause trophic cascades affecting plant and invertebrate abundance. Life-threatening events like escaping a predator can have enduring, even lifelong, effects on the brain, and new interdisciplinary research on the neurobiology of fear in wild animals is both providing insights into post-traumatic stress (PTSD) and reinforcing the likely commonality of population- and community-level effects of fear in nature. […]
Abstract from aforementioned paper
I suddenly thought about our fear of sharks and how sharks might actually be afraid of us. And then I found an article about their fear of orcas:
A team of marine scientists found that great white sharks (Carcharodon carcharias) will make themselves extremely scarce whenever they detect the presence of orcas (Orcinus orca).
“When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year, even though the orcas are only passing through,” said marine ecologist Salvador Jorgensen of Monterey Bay Aquarium.
Maybe vets need to start therapy clinics (I’m only quarter-joking).
Update: Dogs Can Develop OCD Too