Table 2

Data quality definitions for parameters used in Red List assessments for birds, and the number of threatened bird species qualifying owing to good, medium or poor quality data.

data qualitydefinitionno. (%) threatened bird species
goodpopulation size and trend: ‘based on reliable and complete or representative quantitative data’281 (23.2%)
range size: ‘based on polygon boundary largely defined by localities/areas in which the species is known currently (>1980) to occur, and/or by areas of suitable habitat at appropriate elevations where it is thought that it is highly likely to occur’
mediumpopulation size and trend: ‘based on reliable but incomplete or partially representative quantitative data’446 (36.8%)
range size: ‘based on polygon boundary largely defined by localities/areas in which the species is known currently (>1980) to occur, or to have occurred in the recent past (>1970), and/or by areas of suitable habitat at appropriate elevations where it is thought that it is likely to occur’
poorpopulation size and trend: ‘based on qualitative information, but no (or potentially unreliable/unrepresentative) quantitative data’486 (40%)
range size: ‘based on polygon boundary largely defined by localities/areas in which the species is known to occur, or to have occurred, and/or by appropriate buffers and/or geographic features where it is thought to occur’.