A dataset containing UK seabird population size estimates for breeding population size of focal seabird species. A full national census (Seabird 2000) is available for the period 1998-2002, whereas colony counts for a subset of colonies are available for the period 2010-2014 via the Seabird Monitoring Programme (SMP). We used both datasets to derive an estimate of national-level abundance for the period 2010-2014. See methods for further details.