Worldwide, the most important places for habitat-based conservation of birds are the Endemic Bird Areas (EBAs)
. Most species are quite widespread and have large ranges. However, over 2,500 are restricted to an area smaller than 50,000 km2, and they are said to be endemic to it. BirdLife has identified regions of the world where the distributions of two or more of these restricted-range species overlap to form Endemic Bird Areas.
EBAs contain nearly all of the world's restricted-range bird species – only 7% of restricted-range species do not overlap with other such species and therefore do not occur in EBAs. The EBAs also support many of the world's more widespread bird species. Half of all restricted-range species are globally threatened or near-threatened and the other half remain forever vulnerable to the loss or degradation of habitat owing to the small size of their ranges. The majority of EBAs are also important for the conservation of restricted-range species from other animal and plant groups. For example, there is an overlap of 70% between the location of EBAs and areas which are similarly important for endemic plants globally. The unique landscapes where these species occur, amounting to just 4.5% of the earth's land surface, are high priorities for broad-scale ecosystem conservation.
The natural habitat in most EBAs (83%) is forest, especially tropical lowland forest and moist montane forest. Altogether, remaining suitable habitat within the EBAs now covers only 7,300,000 km2, a small proportion of the Earth's land area. Geographically, EBAs are often islands or mountain ranges, and they vary considerably in size, from a few square kilometres to more than 100,000 km2, and in the numbers of restricted-range species that they support (from 2 to 80). EBAs are found around the world, but most (77%) of them are located in the tropics and subtropics.