Fear is a potent emotion. In this study, researchers show that animals not only experience fear, but that the memory of fear has lasting consequences.

Free-living wildlife regularly encounter life-threatening situations. Frequently, this results in some form of non-lethal injury. Giraffes exhibit scars from lions and harbor porpoises show bite and claw marks from gray seals. An astonishing 100% of manta rays bear bite wounds from sharks. It is hard to imagine that these experiences do not cause long-lasting memories of fear.

In this study, researchers confirm that the experience of fear does have lasting effects on wild animals. And while this response has negative implications for reproduction and survival, it also raises a question: is PTSD truly a maladaptive response?

The phrase “fight or flight” was coined in 1915 by W.B. Canon to describe how organisms respond to threats. For decades, this response was thought to be temporary. However, in animal models where, for instance, rodents are exposed to a live cat, the reactions are anything but. While evolution would seem to favor the animal who retains the memory of an encounter with a predator, increased vigilance comes at a cost. It reduces time spent feeding. It also restricts where the animal forages. This animal may have less access to food because they won’t venture into areas it associates with predators. These behaviors are termed the “ecology of fear.” Predators not only kill prey outright but also create life-threatening stress reactions in their prey. Stressed animals do not thrive, nor are they as likely to reproduce or to rear their young to maturity.

Previous research has shown that predator-induced fear affects behavior as well as the levels of stress hormones in wild animals. This study looked for physiological changes in the brains of the animals that would be typical of PTSD. The subjects in the first experiment were 27 wild-caught black-capped chickadees, who react to danger by freezing in place. Researchers exposed the experimental group of birds to calls of known predators, such as the Cooper’s hawk and the northern saw-whet owl. The control group heard non-predator vocalizations.

After seven days, both groups were subjected to a set of predator calls. In contrast to the control group, birds in the experimental group behaved much more fearfully. They froze in place for six times as long as the birds in the control group. Researchers then euthanized all the birds so they could examine their brains for changes characteristic of PTSD. The brains of birds in the experimental group showed changes to the amygdala and hippocampus while the birds in the control group did not. A subsequent experiment involving 22 birds confirmed these physiological responses.

These results meet the criteria to be considered PTSD in a wild animal. They also suggest that PTSD is a natural rather than a maladaptive response to fear. By prioritizing survival above all else, the PTSD response may serve an evolutionary purpose. Put another way, it’s the cost of a brain that ranks quantity over quality of life. It is incredibly unethical that these experiments were conducted on captive animals, however, and it’s not hard to imagine that the experiments themselves would result in trauma and fear ahead of death.

Animal advocates can point to these results as empirical evidence that conditions that induce fear have negative health effects on animals. The emotional well-being of animals matters. Conditions in factory farms, crowds viewing wildlife in national parks or the presence of motorized vehicles in wilderness areas could all create fear. Reducing or eliminating such stressors should lead to better health outcomes and improved quality of life for animals.

