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.

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Comparative analysis techniques have been successfully applied in a number of recent attempts to identify the species traits associated with a current threat of extinction although less often to predict which species may become threatened in the future. Although prediction of risk is obviously a priority, such analyses are undermined by the fact that there may be non-linear and non-additive relationships between the species traits used. A Decision Tree analysis can accommodate with such relationships and here it is used to explore factors affecting extinction risk in parrots. The results firstly verify that simple biological and biogeographical traits can separate threatened from non-threatened species. It is also possible to predict which species are likely to become threatened in the future. The utility of the method is not in testing evolutionary-based hypotheses to explain extinction risk, rather it is a simple and practical method of confirming and/or predicting levels of risk. For well known taxonomic groups it could be used to confirm current IUCN threat categories and identify which species should receive closest attention when the group is next reviewed. For poorly known groups it could be used to predict categories of threat for unclassified species from small groups of classified ones.

In insects, the outcome of intraspecific competition for food during development depends primarily upon larval density and larval sex, but effects will also depend on the particular trait under consideration and the species under study. Experimental manipulations of larval densities of a Madeiran population of the speckled wood butterfly Pararge aegeria confirmed that intraspecific competition affected growth. As densities increased P. aegeria adults were smaller and larval development periods were longer. Sexes responded differently to rearing density. Females were more adversely affected by high density than males, resulting in females having smaller masses at pupation. Survivorship was significantly higher for larvae reared at low densities. No density effect on adult sex ratios was observed. Intraspecific competition during the larval stage would appear to carry a higher cost for females than males. This may confer double disadvantage since females are dependent on their larval derived resources for reproduction as they have little opportunity to accumulate additional resources as adults. This suggests that shortages of larval food could affect fecundity directly. Males, however, may be able to compensate for a small size by feeding as adults and/or by altering their mate location tactics.

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 t o 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. kindly provided very useful discussions and comments on the manuscript. REFERENCESAckerly DD, Donoghue MJ. 1995. Phylogeny and ecology reconsidered. Journal of Ecology 83 730-733. Blackburn TM, Brown VK, Doube BM, Greenwood JJD, Lawton JH, Stork NE. 1993. The relationship between body size and abundance in natural animal assemblages. Journal of Animal Ecology 62: 519-528. Blackburn TM, Lawton JH. 1994. Population abundance and body size in animal assemblages. Philosophical Transactions of the Royal Society London, Series B 343 33-39. Blackburn TM, Gaston KJ, Quinn RM, Arnold H, Gregory RD. 1999. Do local abundances of British birds change with proximity to range edge? Journal of Biogeography 2 6 Bibby CJ. 1994. Recent past and future extinctions in birds. Philosophical Transactions of the Royal Society, Series B 344: 3540. 493-505. CORRELATES OF EXTINCTION RISK 75 ~ ~ Brown JH. 1984. On the relationship between abundance and distribution of species.