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Animals in the Wild Can Get PTSD, Too

Post-traumatic stress disorder has long been classified as a type of mental illness. Now, animal researchers suggest it may actually be an eons-old survival mechanism.

By Tim Brinkhof
Apr 26, 2021 7:00 PM
Cheetah chasing a springbok
(Credit: Elana Erasmus/Shutterstock)


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In the movie Free Willy, a young boy rescues a neglected killer whale from a water park and releases it back into the ocean where it belongs. For an apex predator like Willy, there can be no denying that freedom beats captivity. But for the helpless creatures this killer lords over, it’s quite a different story.

Despite the fact that most living organisms must hunt other living organisms to survive, we often think of the natural world as a peaceful and harmonious place, far from much of the suffering we encounter in our own society day in day out. In truth, many ailments that afflict us humans can afflict animals as well, and PTSD — induced by traumatizing encounters with predators like Willy — is just one example of that.

Two years ago, researchers from Western University set out to test how a prey’s encounter with its natural predators affects its brain chemistry. They split black-capped chickadees into two groups and had one listen to the recorded cries from hawks, owls and shrikes. Analysis showed spiked activity in their amygdala, the area of the brain that organizes memory and influences decision-making through fear and anxiety.

The fact that prey are scared of predators shouldn’t come as a surprise to anyone — least of all biologists specializing in animal behavior. What’s remarkable about this study, is the lasting impact that predator-induced fear can have on the creatures in question. According to the researchers at Western University, these effects actually meet the criteria for what we consider to be post-traumatic stress disorder.

Fight or Flight

Being scared isn’t all bad. “Fight or flight,” the famous phrase first put into words by American physiologist Walter Bradford Cannon over a century ago, illustrates how fear serves an evolutionary purpose by driving prey to escape predators they can’t beat in a fight. The powerful emotion increases heart rate, improves eyesight, opens up airways and pumps oxygen-rich blood into the muscles.

But for all its short-term benefits, fear can also leave lasting detriments. We see this all too often in the human world, particularly among those who suffer from PTSD, perhaps after war or another traumatic event. Loud, unexpected noises like honking cars or fireworks on the 4th of July can teleport veterans back to battle. Sexual assault survivors often have a difficult time being intimate with others, and “moral injury” over the mounting COVID-death toll is plaguing health care workers, even scaring some out of their demanding profession.

But humans aren’t unique in this regard. The aforementioned spike that researchers at Western University detected in the amygdalas of chickadees — a jump of 48 percent in immunoreactivity — manifests into recognizable PTSD symptoms. The birds were either on guard or frozen from fear, two unusual behavioral patterns that continued for a minimum of seven days following the moment they first heard predators approach.

Although plenty of researchers have set up other animal models of PTSD before, the team at Western University refer to their experiment as “the first to demonstrate predator-induced fear can cause enduring effects on the amygdala and hippocampus in a wild animal.” If it withstands the test of time and ongoing research, it might shift the way we think about PTSD and how we go about treating it.

Scared to Death

Ever since PTSD entered the Diagnostic and Statistical Manual of Mental Disorders in 1980, both the medical community and society at large have mostly treated the condition as just that: a disorder, a hyperfunctioning or dysfunctioning of the amygdala. Now that symptoms of the condition are showing up in the natural world, though, biologists have begun to view it not as a disorder but rather as a natural response to stressful situations.

Theoretically, this means the lasting effects of predator-induced fear, just like the short-term benefits, must serve an evolutionary purpose that helps the animal survive. One explanation is that traumatic memories of life-threatening events force an organism to always be on its toes, making it ready to respond should such an event happen again.

To avoid predation, this makes quite a bit of sense. Except that constantly keeping watch for predators that may or may not be lurking in the shadows requires tons of energy. And that energy could otherwise be spent doing more useful things like mating or foraging.  

If animals encounter natural predators on a regular basis — like marine iguanas that must traverse racer snake-infested pits to reach the ocean (dramatically captured on video for Planet Earth II) — paralyzing fear can be detrimental to survival. When ecologists measure the impact that predators have on an ecosystem, they not only factor in the number of prey which were eaten, but also the ones that starved to death because they were too afraid to go look for food.

Ecology of Fear

After weighing potential benefits against well-known detriments, neuroscientist David Diamond and psychologist Phillip Zoladz agreed to define PTSD as the cost of inheriting an “evolutionary primitive mechanism” that values the survival of an organism above the quality of its life. It’s a compelling description, especially when considering that predator attacks are much more common in nature than war is in civilization.

Studies of PTSD in animals are reshaping the debate around PTSD in humans. Some veterans report feeling a sense of shame so strong it can lead to suicide. For them, knowing their condition is not a malfunctioning of the brain but a natural reaction to trauma can be a relief in and of itself. In fact, it’s a guiding principle for compassion therapy, which treats PTSD by helping patients understand their condition from an evolutionary perspective.

The prevalence of PTSD in animals also deals a heavy blow to the romanticized notions about the wild that movies like Free Willy drilled into our skulls. In this sense, the study conducted at Western University is just one of a steadily growing number of research projects which manage to throw a wrench into this alluring but oversimplified narrative regarding the natural world and humanity’s place in it.

As German philosopher Arthur Schopenhauer put it this way a few centuries back: “The bad in the world always outweighs the good. If you don’t believe it, you need only ask yourself whether the pleasure experienced by the predator outweighs the pain of the prey it devours alive.” In other words, confronting pain head-on can be the first step towards making it go away.

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