Over one-quarter of the world’s birds, including nearly three-quarters of those that are threatened, have small ranges. The majority of these restricted-range species occur together in regions called Endemic Bird Areas—mainly in the tropics and subtropics—in just 5% of the Earth’s land surface. A further 10% of bird species are congregatory and very localised at particular times in their life cycles.
Lake Nakuru, Kenya © PAUL GORIUP White-bellied Shortwing © TIM LOSEBY Shola forest, Western Ghats EBA, India P. 23:
© STUART BUTCHART/BIRDLIFE
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Many species have small or restricted ranges Most of the world’s landbirds occupy breeding ranges much smaller than the land areas apparently available to them. For example, among African birds the median range size is equivalent to only 1% of the continental area south of the Sahara. Overall, more than 25% of birds (c.2,600 species) have a restricted range, defined as less than 50,000 km2 (about the size of Costa Rica or Bhutan). Species with small ranges are potentially more susceptible to threats, especially habitat destruction, so perhaps it is not surprising that nearly 70% of Globally Threatened Birds (820 species) have restricted ranges (see box 1).
The location of the world’s 218 EBAs1 Extent and boundary of EBA •
Central point within EBA
Restricted-range bird species occur together in Endemic Bird Areas Nearly all (>90%) restricted-range bird species show range overlaps with at least one other such species. Where this occurs, the 1
combined, often larger region is termed an Endemic Bird Area (EBA). There are at least 218 separate EBAs found across the world, most of them in the tropics and subtropics. The majority of EBAs are also important for
restricted-range species of other animals and plants. For example, there is good congruence (an overlap of over 60%) between EBAs and Centres of Plant Diversity— areas that are important for endemic plants (box 2).
More than 25% of all bird species have restricted ranges, including 70% of Globally Threatened Birds
Many species are confined to small areas of the worlds surface and occur together in centres of endemism. The unique biodiversity concentrated in these small areas is especially susceptible to the destructive effects of humans. In 1987, BirdLife International started a pioneering project to identify these priority areas for biodiversity conservation, using restricted-range landbirds as indicators. Restricted-range species were defined as those landbirds with a global breeding range of less than 50,000 km2 in historical times (i.e. after 1800, when most ornithological recording began). In total, 2,623 bird species (>25% of the total) were identified as restricted-range species, largely occurring in 218 Endemic Bird Areas1,2. Some 820 of these species are currently classified as globally threatened (nearly 70% of all Globally Threatened Birds)3 (see figure). SOURCES 1. ICBP (1992) Putting biodiversity on the map: priority areas for global conservation. Cambridge, UK:
International Council for Bird Preservation. 2. Stattersfield et al . (1998) Endemic Bird Areas of the world: priorities for biodiversity conservation. Cambridge, UK: BirdLife International. 3. BirdLife International (2004) Threatened birds of the world 2004. CD-ROM. Cambridge, UK: BirdLife International.
The relationship between restricted-range bird species and GTBs2,3 100 80
% of species
Many species have small ranges or concentrate at a few sites
Restricted-range species Widespread species
60 40 20 0
All species (n = 9,917)
GTBs (n = 1,211)