Bird colonization of Anak Krakatau, an emergent volcanic island

Abstract

Bird colonization of Anak Krakatau in the 1980s serves as a model for the early colonization processes, which were mostly undocumented, that occurred on the archipelago in the first two decades of this century. Anak Krakatau, which emerged from the sea in 1930, also provides an opportunity to study the formation of an avian communityde novo. Thirty-seven species of birds have been recorded since 1951. Shore birds and aerial insectivores were the first species to exploit the newly emerged island. Plant succession, which is proceeding at different rates on different parts of the island, has provided niches for birds to permanently colonize. Species of open habitats (Caprimulgus affinis, Centropus bengalensis) were the first colonists, followed next by ecological generalists with good dispersal ability (Pycnonotus Goiavier, Halcyon chloris) ; the next species were those that exploit casuarina woodland and forest and the most recent wave of colonists have been frugivores that arrived after figs began to bear fruit in 1985. Three raptors that hunt on the island have limited the colonization of three large frugivores. Most, but not all, colonists have come from the older islands, including those species denied open habitats by plant succession. Comparisons are made with the bird colonization of Rakata during the first two decades of this century. Most birds on Anak Krakatau are insectivores and are restricted to two areas of trees some 12 hectares in total. Foraging methods and sites show little overlap, but dietary analysis in August 1986 showed some common prey items. The very high density of insectivores may be a function of insect abundance on the island and high fecundity and tolerance of crowding by early bird colonists.