Preparing for battle? Potential intergroup conflict promotes current intragroup affiliation

Abstract

Groups of human soldiers increase their affiliative behaviour when moving into combat zones. Despite numerous other species also competing as groups, little is known about how potential intergroup conflict might influence current intragroup affiliative behaviour in non-human animals. Here, I show that allopreening (when one individual preens another) increases in groups of cooperatively breeding green woodhoopoes (Phoeniculus purpureus) when they enter areas where conflicts with neighbours are more likely. Self-preening, which is an indicator of stress in other species, did not increase in conflict areas, suggesting that the change in affiliative behaviour is not the simple consequence of greater stress. Instead, because it is the dominant breeding pair that increase their preening of subordinate helpers, it is possible that current affiliative behaviour is being exchanged for agonistic support in any intergroup conflicts that might ensue. These results are important for our understanding of group dynamics, cooperation and the evolution of sociality, but also bring to mind the intriguing possibilities of social contracts and future planning in birds.

Figure 1.

The influence of potential intergroup conflict on current intragroup; (a,c) allopreening rate and (b,d) allopreening bout duration. Shown in (a) and (b) are means ± s.e.m. from both types of allopreening in all analysis hours (n = 76 h, 12 groups); shown in (c) and (d) are individual group values from paired comparisons of body allopreening in consecutive hours (n = 8 groups). (a,b) white bar, head; grey bar, body.

Figure 2.

Mean ± s.e.m. change in rate of all allopreening (a) receipt and (b) donation by individual group members when moving from core territory areas into zones of potential intergroup conflict (n = 16 dominants and 14 subordinates in eight groups).