It has been decided to follow the categories described in the Checklist of the Birds of Ireland published by the Irish Rare Birds Committee in 1998, with only minor differences. The categories used in both lists however correspond closely (with only minor differences to categories C and D). This list follows the taxonomy and nomenclature of K.H. Voous (1977) and as subsequently modified in reports of the British Ornithologists’ Union Records Committee published in Ibis and British Birds. However, it has been decided to keep those common names which are generally used by Irish observers without ambiguity. These categories and their meanings are listed below:
- CATEGORY A: Species that have been recorded in an apparently natural state in Northern Ireland at least once since 1st January 1950
- CATEGORY B: Species that have been recorded in an apparently natural state in Northern Ireland at least once up to 31st December 1949, but have not been recorded subsequently.
- CATEGORY C1: Species that, although originally introduced by man, have established feral breeding populations in Northern Ireland which apparently maintain themselves without necessary recourse to further introduction.
- CATEGORY C2: Species that have occurred, but are considered to have originated from feral populations outside Northern Ireland.
- CATEGORY D1: Species that would otherwise appear in A or B except that there is a reasonable doubt that they have ever occurred in a natural state.
- CATEGORY D2: Species that have arrived through ship or other human assistance.
- CATEGORY D3: Species that have only ever been found dead on the tideline.
- CATEGORY D4: Species that would otherwise appear in Category C1 except that there is doubt about whether their feral populations are self-supporting.
- CATEGORY E: Species that have been recorded as introductions, transportees or escapes from captivity.
NIBA supports CEDaR (Centre for Environmental Data and Recording) in the Ulster Museum in Belfast. With support from Northern Ireland Environment Agency, information relating to geology and the distribution of fauna and flora is held centrally on computer. This is made available for research, conservation and education purposes. However, the confidentiality of sensitive data is assured. Copeland Bird Observatory, The Raptor Study Group, the Royal Society for the Protection of Birds and the British Trust for Ornithology all contribute data to CEDaR.