Identifying habitat-driven spatial variation in colony size of Herring Gulls Larus argentatus

ABSTRACT

Capsule: Herring Gull Larus argentatus colonies located along coastlines that are relatively sheltered from wave impact, associated with high intertidal prey availability, and with extensive farmland habitat in the vicinity, have increased in size over the last three decades.

Aims: To investigate potential habitat drivers, associated with local food availability, of variation in Herring Gull colony sizes.

Methods: Colony sizes were compared for 68 Herring Gull colonies across southwest Scotland and Northern Ireland to relate to the availability of potential foraging habitats surrounding each colony.

Results: Changes in Herring Gull colony sizes were spatially clustered, with between-colony differences in colony size related to coastline exposure and amount of farmland within the foraging range. At the end of the census period, colonies located in areas with the greatest availability of intertidal prey and farmland habitat were larger compared to those that were not.

Conclusion: Spatially clustered variation in changes of the size of Herring Gull colonies indicates that neighbouring colonies experienced similar environmental conditions and highlights the importance of intertidal and farmland habitats in buffering against declines. This result emphasizes the need for area-specific management for this species of conservation concern.

Acknowledgements

The Seabird Colony Census data were extracted from the Seabird Monitoring Programme Database at www.jncc.gov.uk/smp and www.jncc.gov.uk/page-4460. Data have been provided to the Seabird Monitoring Programme by the generous contributions of nature conservation and research organizations, and of many volunteers throughout the British Isles. We would also like to thank the two anonymous reviewers for their constructive comments that greatly improved the manuscript.

ORCID

Nina J. O’Hanlon http://orcid.org/0000-0001-6396-4518

Ruedi G. Nager http://orcid.org/0000-0003-1129-5724

Additional information

Funding

This work was funded by the European Union’s INTERREG IVA Programme (project 2859 ‘IBIS’) managed by the Special EU Programmes Body.