Relative risk of extinction of passerine birds on continents and islands

Greater numbers and higher proportions of recent species extinctions have b een on islands rather than on continents. In contrast, predictions of massi ve future extinctions stem from the current clearing of continental, tropic al forests(1). For instance, since 1600, 97 out of 108 bird extinctions hav e been on islands(2). However, 452 of the total 1,1 1 1 species currently c onsidered to be threatened are continental(3). Island flora and fauna are u niquely vulnerable to the human introduction of previously absent predators , diseases and other menaces(4), whereas species on continents are not so e cologically logically naive. So could predictions of future continental ext inctions based on island histories be exaggerated(1)? Most threatened speci es have small geographic ranges(5), and the ranges of island species are in evitably smaller than those of continental species. For a given range size, how do the proportions of threatened island and continental species compar e? Here we compile the ranges of the passerine (perching) birds of the Amer icas. Corrected for range size, continental species are more-not less-likel y to be threatened. We use this unexpected vulnerability of continental spe cies with small ranges to produce a map showing where species losses might occur in the long term.