Many bird species have very small ranges and occur together in Endemic Bird Areas

More than 2,500 landbird species have restricted-ranges, often occurring together in ‘centres of endemism’. BirdLife has identified 218 Endemic Bird Areas (EBAs), covering c.5% of the earth’s land area, where the ranges of two or more such species overlap. There is good congruence between global patterns of bird endemism, as shown by Endemic Bird Areas, and those shown by other animal and plant groups. Focusing conservation resources and actions within a relatively small area can therefore help to conserve an important component of the Earth’s terrestrial biodiversity.

Most bird species are quite widespread and have large ranges. However, more than 2,500 species are confined to small areas of the world’s 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 (then ICBP) started a pioneering project to identify these priority areas for biodiversity conservation, using restricted-range landbirds as indicators (ICBP 1992). Restricted-range species were defined as those landbirds with a global breeding range of less than 50,000 km2 throughout historical times (i.e. since 1800, when most ornithological recording began). Where the distributions of two or more of these range-restricted species overlap, they form Endemic Bird Areas (EBAs; Stattersfield et al. 1998).

Following this simple definition, a total of 218 EBAs were identified (see figure 1), covering c.5% of the earth’s land area and encompassing the ranges of 93% of restricted-range birds (2,451 species; Stattersfield et al. 1998). More than 130 “Secondary Areas” were also identified—these support one or more restricted-range bird species, but do not qualify as EBAs because fewer than two species are entirely confined to them. The majority of EBAs (77%) are in the tropics and subtropics. There are approximately equal numbers of island EBAs (105) and mainland EBAs (113). Of the island EBAs, 70% are on oceanic islands, 30% on continental-shelf islands, while for the mainland EBAs, 42% are largely in montane areas, 35% in lowland areas and 24% span both. The predominant natural habitat in most EBAs (c.80%) is forest, especially tropical lowland and montane moist forest. The number of restricted-range landbirds occurring in EBAs varies from two to over 50 (the richest EBAs are the Solomon Islands, the Chocó in Colombia and Ecuador and the Atlantic Forest lowlands in Brazil) (Stattersfield et al. 1998).

Figure 1: Map of the world’s Endemic Bird Areas (EBAs)

A ‘species/area’ curve of the numbers of restricted-range landbirds and the area that they occupy shows that, in 1800, the 2,451 restricted-range species that are endemic to the 218 EBAs were confined to c.14.5 million km2 (c.10% of the world’s land area), and 2,000 of these were confined to less than 4 million km2 (c.2%). In 1998, the same restricted-range species were present in only c.7.3 million km2 of remaining natural habitat (c.5% of the world’s land area; approximately the size of Australia) and c.20% of all bird species occurred in a total of less than 2 million km2 (c.1%) (Stattersfield et al. 1998; see figure 2). These findings show that focusing conservation resources and actions within a relatively small area can help to achieve the conservation of a major part of the Earth’s terrestrial biodiversity.

Figure 2: The relationship between numbers of restricted-range species and the area that they occupied in 1800 and 1998

There is good congruence between global patterns of bird endemism, as shown by EBAs, and those shown by other biodiversity, including other terrestrial vertebrates, invertebrates and plants for which data are available. Overall, more than 50% of EBAs are significant centres of endemism for at least one of these major groups, although their relative importance for different groups is not always the same (Stattersfield et al. 1998). For example, ‘Centres of Plant Diversity’ (CPDs—234 areas with high diversity and/or endemism for plants) (WWF/IUCN 1994, 1994–1995, 1997) and EBAs show good congruence: overall, 70% of CPDs overlap with EBAs, and 60% of EBAs overlap with CPDs. EBAs have also been shown to be excellent indicators of vertebrate and plant diversity patterns in sub-Saharan Africa, due to the common ecological and evolutionary principles on which species’ distributions are based.