T C A Srinivasa-Raghavan: Understanding coalitions

OKONOMOS/ Chimpanzees' inter-group aggression is very similar to human warfare

Some years ago, a group of scientists decided to study the chimpanzees of the Tai Forest in Cote d'Ivoire. They kept at it for 15 years and came up with a fascinating analysis* of chimpanzee behaviour.

The purpose of the study was to analyse the diverse features of the chimp community, including how they formed coalitions.

It turns out that unlike most other animals, chimpanzees show great capacities for cooperation and reciprocal interaction. Most interestingly, they have a highly-developed ability to form coalitions, which are created through what the authors call "explicit social strategies".

They believe that the "chimpanzees' inter-group aggression possesses several features considered typical for human warfare, such as a group enterprise of large coalitions concentrated against neighbour groups. They also suggest that the Tai chimpanzees possess strategies for attack that involve anticipation of possible outcomes.

It seems the Tai chimpanzees have developed "a system of reciprocity in which hunters are rewarded for their contribution." These rewards consist of individual recognition.

Another interesting feature is the survival technique. Chimpanzee life revolves around cracking nuts and the authors explain that nut-cracking involves elaborate planning and a long-term learning phase that can persist for several years.

The second study** suggests that coalitions are common amongst hyenas also, especially the pre-pubertal spotted ones. The existence of coalitions among spotted hyenas has been observed widely and is supported by numerous field observations.

The most common form is the "parallel walk". Here "two hyenas threaten a third by approaching in attack posture, walking shoulder to shoulder almost touching one another. This description, say the authors, fits the definition of a coalition "as an aggressive interaction during which two or more hyenas join to threaten or attack a third animal".

Coalitions, whether amongst chimpanzees or pre-pubertal spotted hyenas, are formed with one objective in mind: to gain control of the pack and the resources available in the area. Coalition formation directly affects dominance status. It also has the indirect effect of "allowing dominant animals to control access to resources".

Wolves are also good coalition formers. "In one colony of 10 to 12 wolves, including multiple males and females whose membership fluctuated from year to year, an average of 5.64 wolves participated in attacks."

What about the inter se relationships within these coalitions? "In considering the relationship between dominance and participation in coalitions, it is necessary to distinguish between absolute dominance rank within a group and relative dominance rank between two individuals."

It turns out that the dominant members initiate and support attacks more frequently than subordinates.

Not just that, subordinate hyenas are targeted more frequently than the dominant members. "Thus, coalition attacks among both spotted hyenas and wolves tend to reinforce the existing dominance hierarchy."

The gains and benefits to individuals that join coalitions have also been studied. It seems close association with the dominants is usually helpful, but not always as it sometimes backfires. This happens when the coalition over-reaches itself during an attack.

The two studies are silent on the issue of coalition leadership. But reading between the lines, amongst the chimpanzees at least, the coalition leader tends to be one that can, in the long run, hold the coalition together.

The hyena coalitions tend to be of much shorter duration and the issue of leadership does not appear important. Thus "there have been no studies of long-term alliances among spotted hyenas or wolves."

However, among free-ranging animals, although attempts have been made to study their willingness to join coalitions, there are no quantitative reports of transitory coalitions.

Finally, since life amongst these forest dwellers is all about survival "" and dominance in order to survive "" family relationship matter a lot. Thus, "both male and female offspring of high-ranking hyenas have competitive advantages, during feeding."

*The Chimpanzees of the Tai Forest: Behavioural Ecology and Evolution by Christophe Boesch, Hedwige Boesch-Achermann. Review available at www.politik.uni-bonn.de/main/doz/kuesters/ hs_kuesters_sose04lit.pdf.

**Coalition formation in a colony of pre-pubertal spotted hyenas by Cynthis J Zabel, Stephanie E. Glickman, Laurence G. Frank, Katya B. Woodmansee, and Geoffery Keppel, www.fs.fed.us/psw/rsl/projects/wild/zabel/zabel6.pdf