Bad moods could be contagious among ravens

Here’s a downer: Pessimism seems contagious among ravens. But positivity? Not so much.

When ravens saw fellow birds’ responses to a disliked food, but not the food itself, their interest in their own food options waned, researchers report May 20 in the Proceedings of the National Academy of Sciences. The study suggests that the birds pick up on and even share negative emotions, the researchers say.

Ravens are “very good problem solvers … but this paper’s really highlighting their social intelligence as well,” says Andrew Gallup, a psychologist at SUNY Polytechnic Institute in Utica, N.Y., who was not involved in the study. The work paints a richer picture of how the birds’ brains work, he says.

Known for their smarts, ravens act in ways that suggest a capacity for empathy, such as by appearing to console a distressed comrade. Thomas Bugnyar, a cognitive ethologist at the University of Vienna, and his colleagues wanted to look into one building block of empathy — whether animals share emotions. To be able to feel for others, an animal needs to be able to feel like others, he says.

But sizing up an animal’s mood is tricky. Scientists generally rely on behavioral or physiological cues to clue into a creature’s emotional state. More challenging is assessing how one animal’s mood might influence another’s: Similar actions appearing to stem from kindred emotions may just be mimicry.

To tune into the moods of ravens, the researchers set up experiments to watch whether the birds reacted positively or negatively to a neutral stimulus. This so-called cognitive bias test, used on a wide variety of animals from bees to pigs, “is basically … asking how you would judge a glass — if it’s half full or half empty,” Bugnyar says.

Eight ravens, tested in pairs, were first given a choice between a box containing a cheese treat and an empty box. Once the birds learned the location of each option, they were given a third box in a new spot that hadn’t been used in the training. Whether a bird acted as if the box was a trick or a treat indicated a cognitive bias, interpreted as pessimism or optimism.

Next, one bird in a pair was offered both unappealing raw carrots and tastier dried dog food before one was taken away. Birds left with the treat moved their heads and bodies as they studied it, while those getting the carrots appeared crankier, spending less time attending to the offering and sometimes kicking or scratching elsewhere. The other bird in the pair watched these reactions from a separate compartment, without being able to see the researcher or which food the bird received.

Both birds then performed the cognitive bias test again. This time, observer birds that had seen their partner appearing perky showed on average the same level of interest in their own ambiguous box as they had previously. But those that had seen their partner reacting negatively typically took more than twice as long to approach the ambiguous box. This dip in the observer birds’ interest was somehow influenced by seeing their partner’s apparent disappointment, the researchers say.

Each bird was tested four times, half of the time with the undesired food and the other half with the treat.

It’s interesting that while the negative responses seemed contagious, the positive ones did not, Gallup says. This may be because negative reactions are easier to provoke or observe, or because animals tune in more to negative information in their environment, the authors say.

The ravens study marks one of the first times the cognitive bias test has been used to examine emotions and social behavior, says coauthor Jessie Adriaense, a comparative psychologist at the University of Vienna. “Emotions are extremely important drivers of our behavior, but how they actually drive animals ... is still an open question,” she says. To truly understand what motivates behavior in animals, scientists need to delve deeper into their emotions, she says.

Editor's note: This story was updated May 20, 2019, to correct the food options offered during the part of the test to determine cognitive bias — it was cheese or nothing — and to correct the number of tests. Each bird was tested four times, rather than the researchers conducting 48 experiments overall.