Indexing winter gull numbers in Great Britain using data from the 1953 to 2004 Winter Gull Roost Surveys

Abstract

Capsule Winter Gull Roost Survey data spanning 50 years were used to generate population indices. Aims To evaluate how wintering numbers of five gull species have changed in Great Britain over the last five decades. Methods Generalized linear models were used to relate gull numbers to habitat, site and year factors, and so derive species-specific indices for nine regions of Great Britain. Regional models considered data from different timescales depending on coverage. Results Patterns of change varied by species and region. All species showed increases in number over the period 1953 to 2004. In most regions, Black-headed Gull Chroicocephalus ridibundus numbers have declined since peaks between 1973 and 1993; Common Gulls Larus canus have also declined recently in some regions. Lesser Black-backed Gull L. fuscus numbers have increased dramatically since 1953, whereas numbers of Herring Gull L argentatus showed large declines between 1963 and 1983. Great Black-backed Gull L. marinus numbers have increased in the west and the Midlands, but recently declined in eastern regions. Conclusions Numbers of wintering gulls in Great Britain have shown rapid changes over the last five decades, reflecting changes in the sizes of breeding populations. These changes are likely to be associated with changes in human activities and resource availability. © 2009 British Trust for Ornithology © 2009 British Trust for Ornithology.