A bird community of lowland rainforest in New Guinea. 5. Mixed-species feeding flocks

Abstract

Data from 300 mixed-species feeding flocks of insectivorous birds in lowland rainforest at Brown River, Papua New Guinea, are analysed. There are two distinct alliances. One is centred around the cooperatively-breeding babbler Pomatostomus isidori. Three other species, a cuckoo-shrike, a pitohui and a honeyeater, mimic the babbler in colour and call, and a fourth, a drongo, mimics the call. Other species, mainly birds of paradise, participate. The second comprises small insectivorous passerines and is centred around the gregarious Gerygone spp. Most participants of both alliances modify their behaviour when in mixed-species flocks. Both diel and seasonal changes occur in the incidence of flocking but the breeding season appears to inhibit flocking much less than expected. Mixed-species flocking appears to be less frequent than in other tropical regions, and possibly less frequent than in montane forests of New Guinea. The high proportion of frugivores in the avifauna, compared to other regions and montane New Guinea, and the small proportion of gregarious insectivores available to serve as 'nuclear' species, are considered to be contributory reasons.