Vocal mediation of foraging competition in the cooperatively breeding green woodhoopoe (Phoeniculus purpureus)

Abstract

Many group-living species produce frequent vocalisations when foraging, but the function of these food-associated calls is often difficult to divine. I investigated the ‘kek’ call of the cooperatively breeding green woodhoopoe (Phoeniculus purpureus), a species in which individuals have preferred foraging techniques dependent on their bill size. Individuals called at a greater rate (1) in foraging compared to non-foraging situations, and (2) in groups containing potential foraging competitors (i.e. individuals that foraged using the same preferred techniques). I therefore asked whether the kek call is used to recruit conspecific foragers or whether it acts as a vocal signal of foraging niche and mediates foraging competition. Foragers that were vocalising were no more likely to be approached than those that were silent, and individuals gained no foraging advantage from the close proximity of another group member. Thus, keks are unlikely to be used to recruit conspecifics. Instead, they appear to regulate spacing between potential foraging competitors. Although an individual forager was equally likely to be closely approached by all other group members, it increased its calling rate only in response to potential foraging competitors. This increase in calling rate resulted in the approaching individual moving away, thus maintaining some separation between individuals that forage in the same way. Maintenance of such spacing is important because the success rate of an individual decreased when a foraging competitor was close by.