Reconciling policy with ecological requirements in biodiversity monitoring

Many of the breeding seabird populations in Britain and Ireland are of international importance; consequently, there is a statutory duty to protect these populations, as part of national biodiversity strategies and under Article 4 of the EU's Directive on the Conservation of Wild Birds (EC/79/409). As part of this process, populations have been monitored annually at a sample of colonies since the mid-1980s and (near) complete surveys have been undertaken twice. Results of this monitoring are currently reported regionally, in an effort to reflect the impact of spatially varying environmental drivers of change; however, there is concern that these regions reflect policy requirements rather than ecological relevance, particularly for mobile species. We used the monitoring data to identify a series of ecologically coherent regions in which trends in abundance and breeding success varied in a consistent fashion and examined how closely the annually sampled data matched the change quantified by the whole population surveys. The number of ecologically coherent regions identified varied from 2 for the northern gannet Morus bassanus and common guillemot Uria aalge to 7 for the great cormorant Phalacrocorax carbo. Trends imputed for ecologically coherent regions more closely matched those observed between whole population censuses and were more consistent than those identified for more policy-driven monitoring regions. By accounting for ecology in the design of monitoring regions, population variation in mobile species can be more accurately represented, leading to the design of more realistic monitoring regions.