Conflict builds cooperation
I just heard an interesting talk by Joan Silk on lasting friendships among female baboons, in which grooming and mutual support during conflicts are both important. Here's a link to some of her papers. This week's paper is on a somewhat-related topic, but in birds rather than apes.
"Duration and outcome of intergroup conflict influences intragroup affiliative behaviour" was just published in Proceedings of the Royal Society by Andrew Radford, of the University of Bristol.
Woodhoopoes are African birds (videos here) that live in small groups, typically a breeding pair and some close relatives. Conflicts over territory with neighboring groups (mostly yelling at each other) are common, often more than once a day. Neighbors rarely take over each other's territories, but if they win the shouting match they stay and forage for awhile. Do such conflicts and their outcomes affect group solidarity?
Radford observed 12 groups in the field over several months. His main measure of positive social interactions within groups was the frequency with which they preen each other's feathers, especially those the birds could have preened themselves. Apparently, getting the back of your head preened is an inalienable right critical to health, but body preening is a perk. (Similarly, in Joan Silk's baboon studies, grooming is a key measure of social interactions.)
Groups that spent more time in conflicts with neighbors (up to 10% of the time!) preened each other more. This was especially true after conflicts a group lost. Interestingly, breeding pairs contributed less to territorial defense, but did more preening, especially after their group lost a conflict. Sort of like George Bush's ""Brownie, you're doing a heckuva job" statement after New Orleans was devastated by Hurricane Katrina.
In addition to the direct benefit of parasite removal, grooming in apes can benefit health by reducing levels of cortisol. (But why would natural selection allow excessive levels of this stress hormone? Because it encourages social interactions with other benefits?) So there could be similar benefits to birds, particularly when feathers being preened are somewhere the bird itself can reach. Being preened after conflicts may reduce the chances of a bird leaving the group or increase their willingness to participate in the next conflict. Anyone want a medal?