Duration and outcome of intergroup conflict influences intragroup affiliative behaviour

Abstract

Theoreticians have long suggested that the amount of intergroup conflict in which a group is involved could influence the level of cooperation or affiliation displayed by its members. Despite the prevalence of intergroup conflicts in many social animal species, however, few empirical studies have investigated this potential link. Here, I show that intragroup allopreening rates are highest in green woodhoopoe (Phoeniculus purpureus) groups that have the greatest involvement in intergroup conflict. One reason for this relationship is a post-conflict increase in allopreening, and I demonstrate for the first time that both conflict duration and outcome influence subsequent allopreening rates: group members allopreened more following long conflicts and those they lost compared with short conflicts and those they won, perhaps because the former are more stressful. The increase in affiliative behaviour was the result of more allopreening of subordinate helpers by the dominant breeding pair, which may be because the breeders are trying to encourage helpers to participate in future conflicts; relative group size influences conflict outcome and helpers contribute more to conflicts than do the breeding pair. These results emphasize that our understanding of cooperation and group dynamics can be enhanced by investigations of how intergroup interactions affect intragroup processes.

Figure 1

Intragroup body allopreening rates of 12 green woodhoopoe groups in relation to the proportion of observation time involved in intergroup conflict. Least-squares regression line is shown.

Figure 2

Intragroup body allopreening rates of 12 green woodhoopoe groups following different intergroup conflicts. Least-squares regression lines are shown: won conflicts (dashed line, diamonds) and lost conflicts (solid line, squares).

Figure 3

Mean (±s.e.m.) post-conflict changes in body allopreening (a) donation and (b) receipt rate for green woodhoopoe individuals of different dominance status (n=20 dominant breeders (white bars), 16 subordinate helpers (grey bars)) in 10 groups.