Non-breeding season populations of seabirds in UK waters: Population sizes for Biologically Defined Minimum Population Scales (BDMPS) (NECR164)

This report reviews evidence concerning the populations of seabirds that are present in UK waters during the non-breeding period. It uses the literature to assess the sizes of seabird populations with the aim to use the most up to date available data (usually expressed in terms of numbers of breeding pairs in each country). It uses data on the demography of seabirds (survival rates, age of first breeding, productivity) to model population age structure in order to assess the numbers of immature birds that are associated with breeding populations, since it is not normally possible to census immature components of seabird populations. Data on the timing of breeding and of migration are used to assess the appropriate seasonal definitions to use in this project; this assessment was based on literature and on appropriate data compliations such as annual bird reports, and online databases presenting seabird migration statistics. For each key species, migratory movements are reviewed based on literature and web pages reporting ring recovery data, geolocator tracking (for the few species for which tracking data are available), seawatching, at-sea survey data, biometrics and other markers of origins of birds.