tags: birds, ornithology, Common Raven, Northern Raven, Corvus corax, animal behavior, animal culture, aggression, dominance hierarchy, social groups, social conflict, post-conflict behavior, consolation, empathy, bpr3.org/?p=52,peer-reviewed research, journal club
Common Raven, Corvus corax, showing off at Bryce Canyon National Park, USA.
Image: United States National Park Service (Public Domain) [larger view]
Humans have long tried to distinguish themselves from other animals on the basis of characters that are perceived to be unique, such as tool design and use, planning for the future and the seemingly "human" capacity for empathy. But one by one, these "unique" characters are found to be shared with other animals. For example, early research shows that making and using tools is shared with our closest relatives, chimpanzees and bonobos. Since we have a shared evolutionary ancestry, this is not terribly surprising. But when a distantly related animal, such as the New Caledonian Crow, Corvus moneduloides, demonstrates that they also are very capable tool-makers and users [DOI: 10.1126/science.1073433], evolutionary biologists sat up and took note. As if that wasn't enough, once again, another feature of human "uniqueness" is being called into question because new research has documented what many bird watchers have known for decades; ravens apparently console their friends after an aggressive conflict with a flockmate.
This is interesting because for a bystander -- a flock member, in this case -- to console the victim of an aggressive conflict, the individual must first recognize that the victim is distressed and then must act appropriately to alleviate that distress, a complex behavior that requires sensitivity to the emotional needs of others -- a trait previously attributed only to humans. Of course after deciding that only humans have this special ability, research has since found that our closest relatives, chimpanzees and bonobos also "console" victims of conflict [DOI: 10.1073/pnas.0804141105], but researchers haven't looked closely at many species.
As bird watchers will tell you, many birds are also highly social and very intelligent, two traits that might be prerequisites for empathy. Although very little is known about empathy in birds, there is some tantalizing evidence that it exists. For example, a recent study of Greylag Geese, Anser anser, found that flock members who observed a conflict involving either their partner or a family member experienced an increase in heart rate (a measure of distress) -- consistent with an empathic response [DOI: 10.1098/rspb.2008.0146]. Another study, this time in Rooks, Corvus frugilegus, shows that members of breeding pairs perform affiliation behaviors following conflicts, suggesting that pair-bonded individuals may actually be consoling their partner when s/he is distressed [DOI: 10.1016/j.cub.2006.11.025].
This evidence is certainly intriguing, but what happens in young birds that have not yet formed a pair bond? Do they form empathetic "friendships"? To answer this question, a team of researchers at the University of Vienna, Orlaith Fraser, a postdoc, and her co-author, Thomas Bugnyar, a teaching fellow, decided to investigate further. They chose to study the Common Raven, Corvus corax. Like the Rook, the Common Raven is another typical member of the corvid family in that they have complex and long-lived social relationships, and their craftiness and intelligence are legendary -- characters that are associated with the capacity to show empathy. Further, ravens are large birds that do not breed until they are between 3-10 years of age, so they are natural choices to study a complex social behavior in birds.
To do this work, Drs. Fraser and Bugnyar removed 13 Common Raven nestlings from four nests (two were zoo bird nests, the other two were wild raven nests) and hand-raised them. After fledging, the young birds were housed together in a large outdoor aviary at the Konrad Lorenz Research Station in Austria in the company of an adult male and female raven who were not related to any of the hand-reared birds. The aviary was made to look as natural as possible, and included trees and other plants, tree trunks and branches, pools of water and stones, and the ravens were given plenty of food and water. (Sadly, the "naturalness" of this enclosure also led to the deaths of two of the young birds who were killed by predators during the course of this study).
Drs. Fraser and Bugnyar began their study by documenting the frequency of affiliative behaviors in these birds, using a standard protocol developed for primate research. They watched the aftermath of 152 fights between these juvenile ravens during the following 23-month period of time, and recorded the identities of the aggressor, the victim and the bystanders (nearby flock members), along with the intensity of the conflict (a chase flight or hitting were rated as "high intensity", whilst a forced retreat was "low intensity"). All affiliative ("consoling") behaviors -- defined as contact sitting, preening or beak-to-beak or beak-to-body touching between the victim of the conflict and an individual flock member -- were recorded during the ten minutes following each conflict. These post-conflict time periods (PC) were then matched to a control period (MC) for the same victim raven on the next possible day and the frequency and nature of the affiliative interactions that occurred in those time periods were compared (Figure 1):
Figure 1. Demonstration of bystander affiliation and solicited bystander affiliation in ravens. Frequency distributions of latency to first affiliative post-conflict interaction directed from a bystander to the conflict victim (A) and directed from the victim to a bystander (B) in post-conflict periods (PCs; filled circles) and matched control periods (MCs; open circles).
Surprisingly, these data reveal that flock members were 2.5 times more likely to offer affiliation to the victim of a conflict without the victim first soliciting it. This occurred most often among those members of the flock that were related by kinship (data not shown), but it still occurred at a measurable rate among unrelated birds.
Was unsolicited affiliative behavior somehow protective for the victim? Actually, no: renewed aggression was just as likely in these situations (Figure 2):
Figure 2. The interdependency of solicited bystander affiliation and renewed aggression between former opponents in ravens. *P < 0.005
There are several interesting things to note here: first, the victims of aggression did not redirect their own aggression towards another individual in their social group. Thus, providing affiliative behaviors to the victim of a conflict didn't carry any exceptional risks to other flock members. Second, since renewed aggression was less likely to occur while affiliation was taking place, the losers tended to actively solicit affiliation from their fellow flock members.
Interestingly, Drs. Fraser and Bugnyar did find that even though the victim was generally at risk for renewed aggression from the same attacker in the immediate post-conflict period, they also found that the victim and aggressor sometimes engaged in affiliation. But this finding was statistically weak, and thus was dismissed as probably being a random event rather than a deliberate strategy to diffuse tension.
Drs. Fraser and Bugnyar also investigated the genetic relationships between victims and flock members who engaged in affiliative behaviors and found there is a relationship (Figure 3):
Figure 3. The quality of bystander-aggressor and bystander-victim relationships in ravens. Results of LMM analyses comparing components (value, compatibility and security) of the bystander's relationships with the aggressor and the victim when post-conflict affiliation from a bystander to the conflict victim occurs.
Basically, affiliative behaviors occurred most often when the flock member had a closer social bond with the victim raven than with the aggressor. Furthermore, the team observed an increasing probability of unsolicited bystander affiliations after more intense conflicts (when the victim was more likely to be distressed). This trend was not seen for solicited affiliations and conflict intensity [data not shown].
"The findings of this study represent an important step towards understanding how ravens manage their social relationships and balance the costs of group-living," Drs Fraser and Bugnyar write. "Furthermore, they suggest that ravens may be responsive to the emotional needs of others."
What does this research mean when placed into a larger (evolutionary) context? As I mentioned, humans have long tried to find those characters that separate us from other animals, yet these same characters, such as tool use, have been found in close relatives. Of course, sharing some characters with other great apes makes sense since we shared a recent ancestor that probably possessed these same characters.
But once again, as with the tool-making crows of New Caledonia, those fascinating birds have confounded this simplistic world view because they share many "special" traits with humans despite the fact that they are not closely related to mammals at all; instead, birds are modern dinosaurs. Birds represent an evolutionary innovation of one branch of ancient reptiles whilst mammals are an offshoot from a different branch of this same clade. Because the reptiles are not known to make or use tools, to plan for the future or express affiliative behaviors, nor any of those other characters that seem to make humans "unique," this raises important questions regarding the "difficulty" of evolving a seemingly complex social behavior, such as consolation/empathy. Or is "empathy" simply part of what comprises a long-term pair bond in a social animal?
Fraser, O., & Bugnyar, T. (2010). Do Ravens Show Consolation? Responses to Distressed Others. PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010605
Wascher, CAF, Scheiber, IBR, & Kotrschal, K. (2008). Heart rate modulation in bystanding geese watching social and non-social events. Proceedings of the Royal Society B 275:1653. DOI: 10.1098/rspb.2008.0146 [PDF]