Mobbing behaviour: reciprocity-based co-operation in breeding Pied Flycatchers Ficedula hypoleuca

Recent non-experimental evidence suggests that reciprocal altruism may be more common in nature than was previously thought. Here we present experimental evidence for mobbing behaviour as reciprocal altruism in breeding Pied Flycatchers Ficedula hypoleuca, a small migratory passerine. Pied Flycatchers attended mobs initiated by their co-operating neighbours. However, they did not join in mobbing initiated by their conspecific neighbours when not assisted in the test an hour before. The results suggest that birds followed a 'tit-for-tat-like' strategy and that responses of neighbouring Flycatchers may be related to reciprocal altruism.