Beyond eight forms of rarity: which species are threatened and which will be next?

We tabulate three measures of rarity: local abundance, breeding range size and elevational extent for the passerine birds of the New World. We determi ne what fraction of species is threatened with extinction within the combin ations of these three measures. Species with smaller ranges., lower abundan ces and narrower elevational bands suffer higher levels of threat across lo wland, montane and island species. For a given range size, lowland species suffer higher levels of threat than island or montane species. (This is cou nter to the intuition that island species - and those isolated on mountain tops might be ecologically naive.) When all three factors are considered to gether, there is only a slight tendency for lowland species to be dispropor tionately more threatened. Simply, island and montane species tend to be re latively common within their restricted ranges and their increased abundanc e reduces their likelihood of being threatened. Elevation is a consistent b ut relatively unimportant factor in determining threat; abundance and range size are much more important, and have an interactive effect on threatened status. We calculate the number of humans with which each species shares i ts breeding range. and find that this number does not aid in predicting thr eat status.