Tests of disperser specificity between frugivorous birds and rainforest fruits in New Guinea

Abstract

Interactions between frugivorous birds and their food plants were studied in tropical lowland hill forest in Papua New Guinea. Over a 2-year period we made intensive observations at 20 fruiting tree species in order to determine avian feeding assemblages at each species. In all, 38 bird species took fruit during observations, mainly in the families Paradisaeidae, Columbidae, Meliphagidae, Campephagidae, Dicaeidae, Zosteropidae, and Pachycephalidae. We tested specificity of bird—plant interactions by examining various statistical associations between bird and plant characteristics to identify key factors in consistent patterns of fruit consumption, if any. Bird families were significantly associated with different types of fruits: cuckoo-shrikes, thickheads and honeyeaters visited figs more often than expected, and birds of paradise and white-eyes visited arillate fruits more often than expected. In other tests, number of visits to very small fruits 5–6.5 mm in diameter (which included several fig species) was correlated with birds ranked by size, especially for berrypeckers, flowerpeckers and white-eyes. However, for both smaller and larger fruits, or for fruits of different structure or accessibility, there was no correlation with bird size. Fruit size showed no correlation with avian food-handling behaviour, or with avian taxonomic affinity. Size of fruiting display was not correlated with either avian residency or nomadism. Our study provided an overview of most of the avian frugivore species at the study site, which fed at a wide array of fruiting plants, and thus our results give an indication of whether patterns in bird—plant relationships are discernible at the level of species, family or guild, or other ecological subset, and whether determining factors might be morphology, size, bird behaviour, etc. These results also provide a broader context within which other regional studies of bird—plant relationships can be interpreted, and were consistent with some, but not all, of the conclusions of previous studies that suggested specialised relationships between Australo-Papuan birds and fruiting plants.