NOLET B, KÖLZSCH A, OOSTERBEEK K, & VRIES P. DE (2014) Stopover sites of Bewick’s Swans Cygnus bewickii identified with GPS loggers. LIMOSA 87 (2): 149-155.

In the classical approach, counts are used to designate sites as important stopovers of migratory birds. Now that individual birds can be tracked on migration by high-tech means, we can also determine which sites are visited most often and/or for the longest periods by tagged birds. The advantage of this alternative method is that remote places will not be underrepresented. Here we illustrate this method with data of Bewick's Swans Cygnus bewickii carrying GPS loggers. In winter 2010/11 a total of 30 Bewick's Swans were caught with cannon nets. Of these, 13 adult females were equipped with neck collars with built-in GPS data-logger (75 g in total), which logged GPS locations (<5 m accurate) eight times a day. Upon returning the next winter, these swans were traced with the help of volunteer observers, and the data downloaded via blue-tooth connection. In total, seven year-round tracks were obtained. A heat-map of the first half of the calendar year revealed clear hotspots in Germany (Emsland and Lower-Elbe/Schleswig-Holstein) and in Estonia, and a smaller one in the Dvina Bay of the White Sea (Fig. 2). A heat-map of the second half of the year showed a hotspot in the Korovinskaya Bay in northern Russia, and in Estonia and Latvia, and further on along the Middle Elbe and in the Netherlands (Veluwemeer, Fig. 3).
      In general, these stopovers are in close agreement with those determined using the classical approach, the exception being the Dvina Bay (White Sea). This site is visited by a large proportion of the population, but stopover duration is only short. Estonia is borne out to be the major spring board to the breeding grounds in northern Russia.

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