Over the past few decades, researchers have started finding behaviors that were once considered uniquely human, like tool use and empathy, in a number of other species. Many of these findings have come from our fellow primates, who presumably share a lot of our evolutionary legacy. But a surprising number of sophisticated behaviors have been showing up in birds, which haven't shared a common ancestor with any mammals for a very long time. The latest behaviors to add to birds' growing list are empathy and consolation, according to a paper released on Wednesday by PLoS one. As the list of complex behavior in birds grows, it seems our expectations for the evolution of behavior may have to evolve, as well.

The finding comes from a study of ravens which spend up to a decade in socially complex flocks before settling down into a pair-bonded relationship. A previous study using other corvids (rooks) indicates that pair-bonded mates will perform what are termed "affiliation behaviors" following conflicts, suggesting that there may be some degree of consolation at play. So, the questions the authors tried to address here was whether, in the absence of pair bonding, the same sort of affiliation would occur within a larger social group where pair bonding hasn't occurred.

The research involved a flock of 13 ravens kept in an aviary, a social group in which a number of the individuals were directly related. As in the wild, the flock displayed various forms of aggression. All of these were recorded over a span of two years, and the researchers looked for signs of affiliation ("defined as contact sitting, preening, or beak-to-beak or beak-to-body touching") or further incidents of aggression. The timing and birds involved in these events were recorded, and the researchers noted whether the victim solicited the affiliation, or whether it was offered spontaneously.

What wasn't observed was the sort of reconciliation that has been seen in chimps. Sometimes, the victim and aggressor engaged in affiliation, but a statistical analysis of these events indicated that they were more of a randomly timed event, rather than a deliberate strategy to diffuse tension. In fact, the victim was generally at risk for renewed aggression from the same attacker in the immediate post-conflict period.

But affiliative displays showed some very clear trends. For starters, the victims of aggression were not likely to lash out at another individual in the social group, a behavior that has been observed in some species. That means approaching the loser doesn't carry any exceptional risks. Affiliation displays also had a practical value, as renewed aggression was less likely while affiliation was taking place. So, it's not much of a surprise to find out that the losers tended to actively solicit affiliation from their fellow flock members.

What is somewhat surprising is that many of those flock members appeared to offer affiliation without a request. This occurred most often among those members of the flock that were related by kinship, although it still occurred at an appreciable rate among unrelated birds. Strikingly, this unsolicited affiliation didn't seem to confer a protective function—renewed aggression was just as likely in these instances.

The authors speculate at length in the paper's discussion about whether those latter events indicate some limited form of empathy, and if they serve to console the victim. It's an interesting question, but one that's extremely difficult to answer, in part because we can't really get inside the mind of a bird, and in part because "consolation" implies lots of context and mental processes, which make determining whether something is consolation a matter as much of semantics as anything else.

Evolutionary parallels across a great divide

What's very interesting, but not discussed at all, is what this means from an evolutionary perspective. We tend to accept that something complex—a gene, a tissue, a behavior—that is shared between two related species probably got to both of them via common descent. But the distance between birds and mammals is immense. Birds are essentially the modern form of the dinosaurs, while mammals are an offshoot of a completely different group of reptiles. In fact, the brains of the two groups are structured differently enough that biologists have struggled to figure out what structures might functionally correspond to each other.

At the same time, these sorts of complex behaviors seem to be absent from many of the species that, if they were really ancient, should also have picked them up from a common ancestor.

The alternative—that they arose separately in these groups—raises a whole series of other questions about behaviors, like consolation, that we tend to think of as complex, and once thought were something that made humans distinct from other animals. Maybe they're not really all that complex, or the selective pressures that produce them are simply common within social species, like the protection from aggression that's offered by affiliation requests seen here. Maybe once a certain behavior like pair bonding evolves, a degree of consolation just comes along for free.

In any case, the fact that we're now finding so many complex behaviors in birds—tool use, problem solving, social learning, planning—may catalyze a significant rethink of what we thought we knew about the biology of behavior.

PLoS one, 2010. DOI: 10.1371/journal.pone.0010605 (About DOIs).

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