Foraging and migratory movements of Caspian terns
In Sweden, the largest breeding colony of this species is the small island of Norra Stenarna, at Fågelsundet in the Baltic Sea (N 60° 37’ 53”, E 17° 55’ 46”) with about 100 breeding pairs each of the last three years. The investigation of the foraging, migration, and wintering strategies of these large populations is important not only for improved understanding of their biology but also for conservation of the species.
In May 2012 and 2013, some adult terns were caught at the nest at Norra Stenarna. To obtain movement paths, the GPS devices (<7.5 g in mass, UvA-BiTS) were attached with Teflon ribbon harness. These GPS devices are solar-powered, provide positional data including speed and altitude, have 3-axis accelerometer sensors, and remote download and configuration. We can download data and send new device configurations when birds are in range of a base-station.
Foraging habitats during breeding and future perspectives
From positional data obtained with the GPS devices, we found that each tern appeared to have several preferred areas for foraging. Those may be important places with high predictability of prey availability. As GPS devices will continue to run throughout the winter after their breeding period, we hope to get movement data for the migration and wintering seasons next spring, when they should return to the colony. It should be exciting to see their journeys over thousands of kilometers.