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A4 – Globally Important Congregations
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The A4 categories apply to those species that are vulnerable as a consequence of their congregatory behavior at regularly used sites, either at breeding colonies or during the non-breeding season, including at foraging, roosting and migratory stopover sites. Such stopover sites may not hold spectacular numbers at any one time, but nevertheless, do so over a relatively short period due to the rapid turnover of birds on passage. For the purpose of the US IBA Program, we define a “relatively short period” as one season – spring, summer, fall, or winter – the dates of which should be determined based on the biology of the species in question.

A4iv The site is known or thought to be a ‘bottleneck site’ where 5% or more of the North American population of a migratory waterbird species, or 5% or more of the global population of a migratory seabird or terrestrial bird species, regularly passes during the spring and/or autumn migration season.

Applying A4iv Criterion
Waterbirds include the following groups or families: Gaviiformes (loons), Podicipediformes (grebes), Anseriformes (geese, swans, ducks), Pelicaniformes (pelicans, cormorants, anhingas), Ciconiiformes (bitterns, herons, egrets, ibis, spoonbills, storks), Gruiformes (rails, gallinules, moorhen, coots, limpkins, cranes), Charadriiformes (all ‘shorebirds,’ gulls, terns, skimmers).

Seabirds include the following groups or families: Procellariiformes (all ‘tubenoses’), Pelicaniformes (tropicbirds, boobies, gannets, frigatebirds), Charadriiformes (skuas, jaegers, alcids).

Terrestrial species include all families not considered waterbirds or seabirds.

This criterion applies to narrow migratory corridors such as narrow sea crossings, mountain ranges and passes, and other local areas where physiographic features concentrate migrants (i.e. not large areas like the entire coast of Texas).

The A4iv criterion can be met if either of the following conditions applies:

  • The number of individuals of a waterbird species passing over a site during the course of spring or fall migration regularly meets or exceeds 5% of the North American population.
  • The number of individuals of a seabird or terrestrial species passing over a site during the course of spring or fall migration regularly meets or exceeds 5% of the global population.

NOTE: This criterion applies to the aerial space the birds fly through and the land/water below it. If threshold numbers of birds regularly stopover at the site then criteria A4i or A4ii applies.

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