Many species have small ranges or concentrate at a few sites

Stuart Butchart/BirdLife Most Endemic Bird Areas are in the tropics and are important for other biodiversity Zoom In

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.

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 pdf case study, box 1).

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 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).

Endemic Bird Areas cover a small fraction of the Earth's land surface

The size of EBAs varies considerably from tiny islands to much larger areas on continents, but together they cover only 14.5 million km². Today the restricted-range birds that characterise EBAs (c.25% of all bird species) are concentrated in just 5% of the Earth’s land surface (box 3). The EBAs of the world are clearly priority areas for action, and key sites within EBAs are included within BirdLife’s Important Bird Areas (IBA) programme.

Many bird species are congregatory, including large numbers of waterbirds and migrants

Many bird species (often with large overall ranges) gather together at various times in their life cycles into large, often spectacular, groups for nesting, feeding, roosting or migrating. In total, nearly 10% of bird species (845) may be classified as congregatory. A large proportion (90%) of these are waterbirds and/ or are migratory (>70%) (box 4). Congregatory behaviour confers many advantages but also vulnerabilities, especially when large numbers of birds make use of just a few important sites. Indeed, some 20% of these species are evaluated as globally threatened. Sites where congregatory species gather in significant numbers are therefore also included within BirdLife’s IBA programme.

Boxes: case studies and scientific analyses

Download SOWB pp.22–23 (PDF, 307 KB) containing the following:

1. More than 25% of all bird species have restricted-ranges, including 70% of GTBs
The relationship between restricted-range bird species and GTBs

2. Most EBAs are in the tropics and are important for other biodiversity
The location of the world's 218 EBAs

3. Restricted-range bird species occur in just 5% of the Earth's land surface
The historical and current relationship between numbers and restricted-range species and the area they occupy

4. Congregation at particular sites is a common behaviour in many bird species
Lesser Flamingo in Africa, soaring birds etc.