Most threatened species have small ranges, rendering them more susceptible to threatening processes. Forty-five percent qualify as threatened because their ranges are less than 20,000 km2, fragmented or restricted to few locations and declining. Three percent (39 species) of threatened species occupy less than 10 km2 globally.
The majority of threatened birds have small or very small ranges. Thirty-nine threatened species (3%) have an occupied range of less than 10 km2, the majority on small islands. For example, Floreana Mockingbird Nesomimus trifasciatus is restricted to two tiny islets totaling just 0.9 km2 in the Galapagos Islands, Ecuador. Caerulean Paradise-flycatcher Eutrichomyias rowleyi has a total range size of 2 km2 on the island of Sangihe, Indonesia. Altogether 558 threatened birds (45%) qualify as threatened because they have ranges that are less than 20,000 km2, declining and fragmented or restricted to a few locations. In total, 634 threatened species (51%) are known from ten or fewer locations, with 450 (36%) found at five or fewer, and 182 (15%) restricted to a single site. For example, Honduran Emerald Amazilia luciae is currently known from just three arid interior valleys of Honduras, while Taita Thrush Turdus helleri is confined to four tiny forest fragments in the Taita Hills, Kenya. The few threatened birds that have very large ranges (128 species or 10% have range sizes over one million km2) are considered threatened either because they have undergone steep population declines, or because they occur at very low densities and have small declining populations. For example, Lappet-faced Vulture Torgos tracheliotus has a range of 8.7 million km2 across much of Africa and the Middle East, but it is estimated that only 8,500 individuals remain and this number is declining.
Related Case Studies in other sections
Compiled 2004, updated 2008, 2011
BirdLife International (2011) Most threatened birds have small ranges. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/109. Checked: 19/12/2013
|Key message: One in eight of the world's birds faces extinction|