Patterns and Causes of Endangerment in the New World Avifauna

Threatened birds of the Americas (1992) detailed 327 species, of which only four had ranges entirely outside the Neotropics, showing how important this latter region is for global bird conservation, contributing 30% of all threatened birds on earth. Brazil had 97 threatened species, Peru 64, and Colombia 56. These countries, plus Mexico, held three-quarters of all threatened birds in the Americas. Over 78% (256) of all threatened bird species possessed ranges of less than 50,000 km2. Some 57% of all threatened birds were confined to wet forest, 17% to dry forest, and 10% to grasslands, a rapidly disappearing habitat type. Over 76% suffered from loss of habitat (for 49% this is the only threat); 16% and 11% suffered significantly from hunting and trade respectively, and 8% were threatened as a function of their restricted ranges. Roughly 30% (twice as many as in Africa) were Endangered (highest category), another 30% divided equally between Indeterminate and Vulnerable, 30% were Rare, and 10% were Insufficiently Known (lowest). Of 146 species in the two highest categories, only nine were under sufficient management regimes, 23 might already have become extinct, 16 needed immediate intervention, and 42 needed very urgent attention. Parrots (28% of New World species threatened) and cracids (26%) suffered disproportionately through the combination of habitat loss and intensive human exploitation (trade and hunting respectively). A key means of saving threatened species lies in the identification and protection of areas in which they are sympatric. The New World, and in particular its Neotropical region, has long been recognized as holding a disproportionately large number of species. Of the world's roughly 9,500 bird species, we compute from a variety of sources that 4,130 (43%) occur in the New World (29% of the planet's land area), and 3,800 (40%) occur in the Neotropics (16% of the planet's land area). The New World's globally threatened bird species, defined according to standard criteria of IUCN (The World Conservation Union), have been listed in six ICBP/BirdLife studies (Anon. 1964; Vincent 1966-1971; King 1978-1979; Collar and Andrew 1988; Collar et al. 1992, 1994). Over the last 30 years the list has expanded five-fold, with most growth in continental South America. It had risen to 360 species by 1988, but with the most detailed and focused review of the situation (Collar et al. 1992), which included the Neotropical Pacific and the Caribbean, the number fell to 327, of which only four occurred entirely outside the Neotropical region. Bibby (1994) showed that the 1988 and 1992 reviews differed by 141 species. Some (24 species) of the discrepancy was because of taxonomic changes or the discovery of new species, but much of it was attributable to precautionary inclusions in the 1988 list (which was in any case preliminary in nature); of 29 species considered threatened for the first time in 1992, 14 had been indicated as "near-threatened" (i.e., subjectively judged as falling close to but outside the boundary for threatened status), and 15 were omitted altogether in the 1988 review. Eligibility for threatened status in both 1988 and 1992 was measured against presently outdated IUCN criteria, the vagueness and subjectivity of which had already led to a search for new criteria based on broadly applicable numerical thresholds (Mace and Lande 1991; Mace et al. 1993). Under the old criteria, a species was considered threatened if, by virtue of a declining world population or small range, it was somehow deemed to be at imminent or steadily increasing risk of global extinction. Under the new criteria issued in draft to the IUCN General Assembly in January 1994 and condensed in tabular form in the introduction to Collar et al. (1994) the same process of analysis was objectified and rendered more rigorous by the introduction of numerical thresholds for population sizes, range sizes, and decline rates. Nevertheless, use of the new criteria in 1994 largely confirmed the number and composition of the New World's threatened species in 1992. (Differences in composition from the 1994 list mostly involved transfer of species between the threatened and nearthreatened lists, not movement onto or off the non-threatened list.) In this paper we analyze the