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Foraging and migration movements of lesser black-backed gull

The eastern race of lesser black-backed gull (silltrut, Larus fuscus fuscus) is red listed in Sweden, for it underwent steep population declines through the last decades, in common with other populations of this race, but in great contrast to the western races (L. f. intermedius and L. f. graellsii). The decline is not fully understood, however the leading theory is that the races have divergent migration routes, with L. f. fuscus wintering in eastern Africa where they may be exposed to bioaccumulant chemicals.

This study looks to better understand the full annual cycle of these gulls through continuous GPS tracking throughout the year. Through a collaborative project the other races will also be tracked. The GPS device we use gives extremely detailed behaviour data, allowing for fine scale movement activity to be studied along with larger scale location of foraging areas and migration behaviour.

Methods

Lesser black-backed gull

In May 2011, ten adult gulls were caught at the nest. Small (~18 g) solar powered GPS devices were attached using a harness. The study population was at Stora Karlsö a small Swedish island in the Baltic Sea. GPS devices are solar-powered, provide positional data including speed and altitude, have 3-axis accelerometer sensors, and remote download and configuration. We could download data and send new device configurations when birds were in range of a base-station. GPS devices will remain on throughout the winter: Migration data can be gained in 2012 for birds returning to the colony.

Fine-scale flight behaviour

GPS tracking

With high resolution GPS tracking (e.g. 10 s intervals as here), along with altitude and instantaneous ground speed, it is possible to build up a very detailed picture of a birds flight behaviour. The example here shows a gull on a homeward flight, following closely a cliff around a nearby island, as it does this the bird gains altitude, presumably using updrafts. As it leaves the island it drops in altitude gradually, converting this potential energy into kinetic energy for forward motion.

Long post-breeding trips

Movement tracks

Post-breeding, some individuals make very long multi-day trips. Some may represent exploration behaviour, looking for new breeding sites for future seasons; others are likely longer foraging trips.

Page Manager:

Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden