Now, more and more researchers are investigating whether this contagiousness is something seen throughout the animal kingdom.
Scientists hope to find out if stress can pass through completely separate channels of raised screeches, squeals and hackles. What they learn could shed light on the treatment of animals and shed light on the nature of stress in humans.
The researchers are “trying to understand how these processes can occur simultaneously across different taxa in birds, in humans, in fish, in mice, so that you have the same phenomenon occurring in very different species that have evolved on a very different level,” says Jens Pruessner, professor of psychology at McGill University in Montreal.
You have probably experienced stress contagion. A friend walks by and spends a few minutes complaining about his job or his partner. Suddenly, even though these aren’t your problems, you’re breathing faster and feeling a little nervous.
That’s because, as you’ve heard, your body has given you a quick shot of adrenaline and cortisol — hormones that mobilize energy stores to run, fight, and complete projects on schedule. Much research shows that over time, frequent jolts of stress are corrosive to the body and the reproduction.
Neuroscientist Jaideep Bains studies how stress imprints itself on the brain.
In 2014, Bains began studying in his lab at the University of Calgary how stress jumps from individual to individual in mice. He discovered that a stressed mouse emits a pheromone from its anal glands, which is then sniffed out by a nearby mouse.
“That makes sense, right? said Bains. “If you think about what a mouse would do, it could be out in the field and being chased by a predator, and it comes back to the nest.
“A vocal signal would probably attract attention, but a quiet chemical signal, which is only detected by those very close to you, would be a great way to let others know there is danger,” said added Baths.
Bains found that neural connections in a mouse that senses stress pheromones change to become identical to the mouse that first sensed the stressor. So the brain of a mouse that sensed a stressed mouse also seems to sense a stressor.
Next, “we… asked if a stressed mouse could transmit information to a second mouse, and if this the mouse could then take it to another one mice,” Bains said. “And it works wonderfully. The third mouse shows the same changes in its brain.
This also has implications for humans. Like mice, we sense the anxiety of others.
“We really see ourselves as individuals with our own experiences,” Bains said. “And we don’t think much about how other people’s experiences and what they’re going through might also shape us.”
Measuring stress in wild animals is difficult outside of a neuroscience lab. Scientists are considered predatory by most species and trigger a stress response simply by their presence. Animals leave traces of stress hormones in their feces and feathers, but these are not real-time samples. And capturing animals to test their blood hormones is itself a stressful process for animals. However, new technologies make the job easier.
Hanja Brandl from the University of Konstanz in Germany studies guinea fowl in Kenya using small implanted heart rate recorders combined with solar-powered GPS trackers to observe how stress passes from bird to bird. Similar results studies suggest that stressed birds have higher heart rates and, among other behaviors, tend to stay closer to their flocks.
Brandl and his colleagues also use video camera traps — cameras triggered by animal movements — and machine learning in other studies.
“Knowing who goes where and how often they feed can reveal stress,” says Brandl.
Machine learning also gives scientists better data from hours of video. Before deep learning algorithms, Brandl had to watch videos for long periods of time, accounting for sometimes ambiguous behaviors. Now the algorithms pick up on tiny nuances.
“By giving the computer thousands and sometimes millions of data points, I’m basically letting the computer decide,” she says.
Scientists have also observed that groups working together to relieve stress in anxious individual members. For instance, vampire bats appease members of their social network by sharing food.
Research is already affecting breeding. Studies have shown that calves recover faster after dehorning when allowed to return to their social group, and the chicks benefit to to be near their mother hen after undergoing a slight stress.
“It’s very relevant. … It’s like a child who has a little accident in the playground. And with mom there, everything will probably be fine,” says Brandl.
Brandl wrote a journal article in the Proceedings of the Royal Society B this year calling for further study of the transmission of stress in animals.
“More information from animal social systems research is needed to unravel the mechanisms and consequences of stress transmission,” she writes. “Identifying the extent to which stress transmission modulates animal collectives represents an important line of research.”
“At the moment, we’re just taking the first steps, trying to figure out how important stress transmission really is,” says Brandl. But with more studies and more discoveries, “we can really refine all the actions that improve animal welfare in captivity and in the wild.”
Bishop Sand is an audio producer at the Washington Post.
