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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.

Applying A4i 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).

The A4i criterion can be met if either of the following conditions applies:

• The number of individuals of a species in roosts, breeding colonies, feeding flocks or at a migratory stopover site regularly meets or exceeds 1% of the North American population ‘simultaneously’. The U.S. IBA Committee will use reason to further define ‘simultaneously’ in each case. If the case can be made that counts of a large area over the course of a few days or so represent a snapshot, then the data do not all have to be collected in one day.
• The number of individuals of a species at a migratory stopover site regularly meets or exceeds 5% of the North American population over the course of the season.

Download List and Thresholds for A4 - Waterbird, Seabird, and Landbird Species (pdf)

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Updated June 2012