Ravens' moods are affected by the emotions of other ravens around them, even when they can't see what's causing the fuss. Marcin Perkowski/Shutterstock

George RR Martin may have made ravens the messengers of Westeros because they're more goth than homing pigeons, but he was onto something about their capacity to communicate. However, only a capacity to transmit subjective judgments to each other, rather than to distant people, has been proven. Nevertheless, it's a significant discovery in terms of animal intelligence and the capacities needed to live in groups.

Living together is hard for animals that are sometimes in competition for food, nesting sites, or mates. Zoologists are interested in learning about what makes it possible – for one thing, it might help us understand how we can get along without stabbing or poisoning each other. “Emotional contagion”, where an individual spreads their mood to those around them, has been proposed as an important capacity, but only so far proven in primates.

University of Vienna PhD student Jessie Adriaense manipulated the emotional state of ravens (Corvus corax) while others watched, to see if the observer got the message of how the first raven was feeling.

Previous studies, across many species, have run into criticism the second might be responding directly to whatever is affecting the mood of its fellow, rather than experiencing a second-hand shift. Adriaense paired ravens up in cages where they could watch each other. One raven, dubbed the demonstrator, was shown two food items, one liked by corvids, the other something they will only eat when nothing else is available. One was then taken away, while the other was handled to hint to the demonstrator raven it would be offered as a reward.

In Proceedings of the National Academy of Sciences, Adriaense reports that, as expected, the ravens' responses were very different between these cases, losing interest when the likely reward was less tasty.

This raven "joey" has some confidence the contents of the box it is pecking at will contain something exciting because its spirits were raised by seeing a bird in a neighboring cage getting excited at a likely treat. Jessie E.C. Adriaense

Of more interest was what the observer raven did. Without much happening in their own cage, observers spent three-quarters of their time facing the demonstrator. Although they could not see the items being shown to the demonstrator, observers could see their reactions, and their own responses were strongly influenced by this.

When a box with a hidden item was put inside the observer's cage, the response depended on what they had seen from the demonstrator. If they'd seen it show excitement at a likely treat the observer was quick to go and peck at the box. If the demonstrator had shown disappointment however, the observing raven showed what Adriaense calls pessimism, taking a long time before bothering to investigate what they had been offered.

The results lend support to the still-controversial claim birds are capable of empathy, once thought restricted to mammals (and possibly dragons), and provide a possible pathway for the development of important group behaviors.