Have you ever visited a seabird colony in autumn or winter? Compared to the hustle-bustle during spring and summer, it is very quiet then. No sign of guillemots, kittiwakes and Co., only empty nests remain. Where do all these seabirds go after they have raised their young?
Atlantic puffin with fish for its chick and light logger attached to the yellow leg ring.
Most seabirds are true migratory species, and many species travel far and wide outside the breeding season, and really only come to land to mate and raise their young. Through the MARCIS project we want to understand how seabirds are affected by human stressors in marine areas. Knowing where seabirds are and how they use their marine habitat is the first step, and MARCIS builds on the long-term monitoring and mapping programme for seabirds, SEAPOP and SEATRACK. During the breeding season, the movement behaviour of seabirds can be studied using GPS tracking technologies (read our story on GPS-tracking here).
To study movement behaviour outside the breeding season, GPS devices for most seabird species are too heavy, have a too small battery capacity, and would not stay attached to the birds for long enough. Therefore, another type of logger is used: Light loggers, also called geolocators or GLS loggers weigh only 1-2 g, depending on the model. They record daylength, light intensity and period of daylight for each day.
Different types of light loggers. Right: Light logger attached to the leg of a common guillemot.
Using information about sunrise and sunset, the approximate position can be back calculated with an accuracy of approximately 200 km. In regards to accuracy, light loggers are therefore lagging behind GPS technology. However, even the lightest models record data for more than one year, and they are small and light enough to be attached to even the smaller seabird species such as puffins and black-legged kittiwakes. In comparison to the enormous distances that seabirds may travel between two breeding seasons (e.g. black-legged kittiwakes from central Norway overwinter near the coast of New Foundland south of Greenland), the accuracy of 200 km is also less of an issue. To keep the logger attached for a period of at least one full year, the logger gets attached to the bird with a plastic leg ring. Most light logger models are further equipped with a wet-dry sensor, which registers if the logger is immersed in water (e.g. if the bird is swimming or diving) or whether it is dry. This helps to assess the birds’ behaviour in addition to their location.
Common guillemot with a light logger attached to the blue leg ring.
Since seabirds come to land to breed during spring and summer, and tend to return to their nesting site each year, this is the ideal period of the year to conduct fieldwork. In the SEATRACK framework, hundreds of seabirds in 56 colonies in the North Atlantic are equipped with light loggers each year, and researchers attempt to recollect as many of these loggers as possible in the following year. Now, in August, seabird chicks are fledging, and the breeding season and thus also the fieldwork period, is coming to an end. Hopefully, many birds with loggers have returned to their colonies, delivering important data about their whereabouts. If you are curious about where seabirds spend the non-breeding season, you can explore the SEATRACK website and check out where the birds travel!
Map from the SEATRACK Web Application showing the winter distribution of black-legged kittiwakes from the Sklinna/ Sør-Gjæslingan colony. The darker the orange shading, the higher the probability of birds being in the area.
Black-legged kittiwake attending its chick at Sør-Gjæslingan. The light logger is attached to the green leg ring.