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Foraging and migratory movements of Caspian terns

The Caspian tern (Hydroprogne caspia) is the largest tern species, which has a wide breeding distribution throughout the world. However, little has been known about their movement strategy during foraging and migration because they range outside of areas where we can observe them directly. We are now trying to reveal their movement patterns by tracking them with novel GPS devices.

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.

Caspain terns
Photo: Kozue Shiomi

Methods

Caspian tern with GPS
Photo: Kozue Shiomi

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

Tracking
Photo: Kozue Shiomi

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.

Page Manager:

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