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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