The effects of selective logging and other types of forest exploitation on bird communities are often studied latitudinally, i.e. a contemporaneous comparison of disturbed and pristine areas. Such an approach assumes that before disturbance those areas were equivalent. By comparing communities at a single site before and after disturbance, a so called longitudinal approach does not make that assumption but such studies can be resource intensive. In this study we adopt a latitudinal approach to explore the effects of disturbance on birds, but pay specific attention to whether natural geographically-based variation in the forest ecosystem may be a major contributory factor equal to, or greater than, effects of disturbance. Bird census data were collected from two Indonesian islands, Sumba and Buru. On Sumba the differences between habitat types in terms of species richness, species accumulation rates, and numbers of birds were swamped by simple site differences between the forest blocks sampled. On Buru, disturbed areas were more diverse than mature forest but it was still not possible to discount the effects of natural variation between forest areas. Although the islands support bird faunas which are rather similar in size and origin, local species diversities and abundances were significantly greater on Sumba. Substituting space for time is a common strategy in ecological research but the results of such studies should be viewed with caution.

Size of distributional range, position in the range, body size and diet are some of the ecological traits that may correlate with local abundance. Evolutionary phenomena such as taxon cycles, acting over much greater time periods, may also influence abundance and promote species extinction. This paper assesses which of a wide range of ecological and historic traits best predict the variation in abundance of tropical forest birds on Sumba and Buru islands in Wallacea (Indonesia). In addition we seek to determine which traits predict species' ability to adapt to secondary or logged forest. The most important correlates of both abundance and ability to transfer were those related to the evolutionary history of the species within the Wallacean Archipelago and not the traits that were more directly related to species ecology. These relationships are maintained when allowance is made for phylogenetic relationships. Our interpretation of the results is that recent colonists to an island are initially rare in the indigenous forest habitat but concomitant with an adaptation to local conditions they gradually become more abundant and taxonomically distinct from other populations of the same species. These results apparently contradict the taxon cycle hypothesis but this may be a result of our focus on indigenous forest habitats rather than on a wider range dominated by anthropogenic ones.

The island of Buru in Maluku province, Indonesia was visited in November and December 1989. Using a point count method, we assessed the conservation status of the island's restricted-range lowland birds by examining their abundance and habitat associations. Thirteen of Buru's 19 lowland restricted-range species were recorded during the fieldwork. Of these we assign nine (White-eyed Imperial Pigeon Ducula perspicillata , Moluccan Red Lory Eos bornea , Bum Racquet-tail Prioniturus mada , Black-tipped Monarch Monarcha loricatus , White-naped Monarch Monarcha pileatus , Dark-grey Flycatcher Myiagra galeata , Flame-breasted Flowerpecker Dicaeum erythrothorax , Bum Yellow White-eye Zosterops buruensis and Black-faced Friarbird Philemon moluccensis ) to IUCN's Safe/Low risk category of threat, on the basis of their large populations, widespread occurrence on Bum and association with non-pristine habitats. We recommend that the remaining six of the recorded species remain Data-deficient but some of these (e.g. Blue-fronted Lorikeet Charmosyna toxopei and Bum Cuckoo-shrike Coracina fortis ) may be Vulnerable. While data on the birds which we did not record are obviously needed, we suggest that the amount of forest remaining, the abundance of many species and their tolerance of selectively logged forests bodes well for the immediate future of the bulk of Buru's lowland avifauna.

SummaryThe island of Sumba was visited in 1989 and 1992 with the aim of collecting data on its avifauna. The endemic and other restricted-range bird species are very poorly known and, potentially, at great risk from extinction due to habitat change. Using standardized methods, habitat and bird census data were collected in eight forest areas. Analysis of the habitat data shows that most of the restricted-range species are forest-dependent. The exception is Turnix everetti (Sumba Buttonquail), which is found in open grassland. Discriminant Function Analysis was used to define habitat associations in a more precise and objective way. The species with the most specific requirements are Ptilinopus dohertyi (Red-naped Fruit-dove) and Zoothera dohertyi (Chestnut-backed Thrush), which are associated with primary forest at high altitudes, and Cacatua sulphurea (Sulphur-crested Cockatoo) and Rhyticeros everetti (Sumba Hornbill), which prefer evergreen primary or mature secondary forest at low altitudes. The results of the bird censuses were combined with data on habitat cover from satellite photographs to produce estimates of total population sizes. Among the rarest and most endangered species on Sumba are three which are represented by endemic subspecies: C. sulphurea (estimated population 3,200 birds), Eclectus roratus (Eclectus Parrot) (1,900), Tanygnathus megalorynchos (Great-billed Parrot) (1,700). The rarest endemic species is R. everetti, with a population of approximately 6,500. It is suggested that the census method used – point counts With distance estimates to bird contacts – is the best compromise for multi-species surveys in tropical forests.