Geophagy in New Guinea birds

Geophagy, the ingestion of soil, has been reported for birds and other anim als from many regions, but its functions remain debated. We report geophagy for the first time for New Guinea birds: four or five parrot species, two or three pigeon species, one hornbill species, one crow species and possibl y one cassowary species. These species ate soil at an area of bare ground c reated by a landslide on a steep mountain slope. Parrots visited the site i n the early morning, pigeons in the late afternoon, flying in from consider able distances. All 11 of these species are frugivores. In the: vicinity, w e-recorded 133 other bird species (including 37 other frugivore species) th at were not observed to visit the site. Within each taxonomic group of frug ivores, those practising geophagy tended to be the largest species of their guild. To test hypotheses regarding the functions of geophagy, we carried out chemical and physical analyses of soil samples from the site. The inges ted soil was much too fine-grained to be useful as grit; it contained only modest levels of all 14 minerals analysed; it lacked buffering capacity; an d there was no evidence that it protected against diarrhoea. Instead, the s oil's high measured cation-exchange capacity, high content of cation-bindin g minerals and binding of large quantities of tannic acid and quinine sugge st a different hypothesis: that geophagy in this case served to bind poison ous and/or bitter-tasting secondary compounds in ingested fruits and seeds. Geophagy thus represents one weapon in the escalating biological warfare b etween plants and animal consumers an evolutionary arms race at which parro ts excel. We discuss five unsolved problems posed by geophagy.