Surveying waterbirds away from major waterbodies: implications for waterbird population estimates in Great Britain

Abstract

Capsule Population size estimates of widely dispersed waterbird species in Great Britain were improved using a stratified random sample of habitats in addition to standard counts of known wetlands. Aims To improve the estimation of national population sizes for species less well covered by the UK Wetland Bird Survey (WeBS) using a stratified random sampling approach. Methods Observers recorded habitat type and waterbird numbers within a stratified random sample of 1-km grid squares across Great Britain. For 20 species, population sizes were estimated using boot-strap techniques. These totals were added to WeBS Core Count and Non-Estuarine Coastal Waterbird Survey (UK-NEWS) data and the resulting Dispersed Waterbird Survey (DWS) estimate compared with published national population estimates. Results DWS estimates exceeded published national estimates by more than 50% for eight species but were lower for Pochard Aythya farina, Goldeneye Bucephala clangula and Moorhen Gallinula chloropus. Conclusions Our analyses suggest that the DWS provides a useful source of supplementary information for several dispersed species and demonstrates the value of a stratified random sampling approach for monitoring waterbird populations.