BTO: Gulls are not just loitering . . .

Lesser black backed gull by Edmund Fellowes ANL-140819-100239001
Lesser black backed gull by Edmund Fellowes ANL-140819-100239001
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An image sent in by email and showing two gulls standing on a beach reunites me with an adult lesser black-backed gull first encountered a few weeks earlier and 600 miles further north.

That this was the same gull, the only adult to have been ringed during the annual monitoring of the nesting colony on the tiny island of Flatholm, was revealed thanks to the numbered blue ‘darvic’ ring that the bird carried on its left leg.

Flatholm, a small island located just south of Cardiff in the Bristol Channel, is home to a large and mixed colony of nesting lesser black-backed and herring gulls. Each year, a team of licensed bird ringers joins members of the Flatholm Society to survey the colony and to fit a sample of the birds with coloured rings. These rings carry a short sequence of large letters and numbers, allowing the bird to be identified if seen by a birdwatcher. Almost every bird ringed is a chick but very occasionally an adult is caught. F140 was the only adult caught and ringed this summer, so to get a record back provides very valuable information.

A number of the chicks from this summer’s visit have also been spotted. As was the case with F140, several of the chicks had been seen by birdwatchers visiting the beaches of northern Spain, an area used by many of those British lesser black-backed gulls that move south in the autumn. Some of these birds will push even further south to reach Africa.

Most of our knowledge of these movements comes from bird ringing but new technologies are providing other ways of following the movements of our gulls. Lesser black-backed gulls breeding at Orford Ness on the Suffolk coast have, for example, been tracked with electronic devices that record the bird’s location. These tags, fitted by BTO researchers, are solar powered and download the information collected automatically, once the birds move to within a few kilometres of a mast located at their breeding colony. In addition to the gulls’ position, the tags record information on the altitude of the bird and the acceleration during flight. Not only does this work tell us about where the birds feed and spend the winter, it can also tell us how they respond to windfarms and other components of the marine environment.

It is the colour rings, however, that remain more widely used because they are a cheaper technology and allow researchers to follow the fortunes of a larger sample of birds.

The efforts of birdwatchers, who submit their sightings of colour-ringed gulls, then help to build up a picture of gull movements. So, while casual observers might assume that gulls don’t do a great deal other than loiter on the coast or nearby pig fields, the rings and tags reveal that many gulls lead far more interesting lives. Find out more at www.bto.org/science/migration/tracking-studies/tracking-lesser-black-backed-gulls