Some IBAs hold the last populations of highly threatened bird species and are an urgent priority

Tahiti Monarch Pomarea nigra © MANU

The Alliance for Zero Extinction (AZE), of which BirdLife is a founding member, aims to identify sites that hold the last remaining populations of highly threatened species. Such sites are among the most urgent priorities for appropriate protection and conservation action. For birds, AZE sites can be viewed as a critical subset of Important Bird Areas (IBAs)—the last line of defence in preventing imminent avian extinction.

The Alliance for Zero Extinction (AZE) is a joint initiative of 52 biodiversity conservation organisations, including BirdLife International and a number of national BirdLife Partners. Its aim is to identify and safeguard sites holding the last remaining population of highly threatened species. To date, AZE sites have been identified for a number of taxonomic groups, including mammals, birds, some reptiles (crocodilians, iguanas, turtles, and tortoises), amphibians, conifers and corals.

The diagram below illustrates how AZE sites form subsets of Important Bird Areas (IBAs) and Key Biodiversity Areas (KBAs).

AZE sites are identified using the following criteria (Ricketts et al. 2005):

Endangerment: An AZE site must contain at least one Endangered (EN) or Critically Endangered (CR) species, as listed on the IUCN Red List.

Irreplaceability: An AZE site should only be designated if it is the sole area where an EN or CR species occurs or if it contains the overwhelming proportion of the known resident population of the EN or CR species for at least one life history segment (e.g., breeding or wintering).

Discreteness: The area must have a definable boundary within which the character of habitats, biological communities, and/or management issues have more in common with each other than they do with those in adjacent areas (e.g., a single lake, mountaintop, or forest fragment).

This approach alone is, of course, not sufficient to prevent all extinctions. Many highly imperilled species are not confined to a single site. For example, Asia’s Gyps vultures have experienced a catastrophic decline over the last two decades but remain widely distributed. Furthermore, effective conservation needs to move beyond site-specific strategies and address threats to biodiversity and ecological processes in the wider landscape. Despite this, many species are now so threatened  that without immediate, targeted action at key locations they are likely to disappear forever. AZEs represent centres of imminent extinction and are urgent and compelling priorities for conservation action.

As of the 2010 update of the AZE inventory, a total of 588 AZEs have been identified. These sites represent the last remaining populations of some 920 ‘trigger’ species, including 200 bird species—21% of AZEs are triggered by birds alone, 4% are triggered by both birds and other taxa, and around 25% are triggered by other taxa but also qualify as IBAs (for the less threatened or more widespread bird species that occur in them). Despite the obvious importance of AZE sites, only 22% are fully protected, whilst 27% are partially protected and 51% remain unprotected. By drawing global attention to these critical sites, it is hoped that the AZE initiative can help secure the future of some the world’s most threatened species.

List of AZE bird trigger species



Ricketts, T. H., Dinerstein, E., Boucher, T., Brooks, T. M., Butchart, S. H. M., Hoffmann, M., Lamoreux, J. F., Morrison, J., Parr, M., Pilgrim, J. D., Rodrigues, A. S. L., Sechrest, W., Wallace, G. E., Berlin, K., Bielby, J., Burgess, N. D., Church, D. R., Cox, N., Knox, D., Loucks, C., Luck, G. W., Master L. L., Moore, R., Naidoo, R., Ridgely, R., Schatz, G. E., Shire, G., Strand, H., Wettengel, W. and Wikramanayake, E. (2005) Pinpointing and preventing imminent extinctions. PNAS 102: 18497–18501.

Compiled 2011

Recommended Citation:
BirdLife International (2011) Some IBAs hold the last populations of highly threatened bird species and are an urgent priority. Presented as part of the BirdLife State of the world's birds website. Available from: . Checked: