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The B4 category applies 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 ‘regularly short period of time’ 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 B4ii Criterion
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.

The B4ii 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 migratory stopover sites 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 must regularly meet or exceed 5% of the North American population over the course of the season.

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