The role of toxic pitohuis in mixed-species flocks of lowland forest in Papua New Guinea

In many animal taxa, non-toxic species demonstrate Batesian mimicry – appearing or behaving similarly to harmful species – thereby reducing their attractiveness to predators. A potential example of Batesian mimicry occurs in Papua New Guinea (PNG), where birds of the genus Pitohui have been found to contain toxic compounds; pitohuis are frequent members of mixed-species flocks and several observers have hypothesised that species in flocks are imitating each other in their plumage and vocalisations. If non-toxic species participate in flocks to associate with pitohuis, we predicted that pitohuis should play an important role in flocks, such that flock composition should be strongly influenced by their presence, and that other species should be attracted towards their vocalisations. We found, however, that in the lowland rainforests of Madang Province, flock composition was less influenced by the presence of pitohuis than by the presence of Rufous Babblers (Pomatostomus isidori), a non-toxic leading species. In playback experiments, Rufous Babblers were as attractive to heterospecifics as pitohuis. Our study provides the first empirical test of the connection between toxicity and flock organisation in PNG and our primarily negative results suggests that toxicity does not drive the organisation of flocks in our study area.