weblog 2011

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Migration logged

26 June 2011 18:00

Photo Øystein Varpe

Today, I am mapping nests of Barnacle Geese on Storholmen and I am looking for birds with GLS-loggers. Øystein Varpe had spotted a pair with these on Juttaholmen 22 June 2011 and sent me this picture. A GLS-logger registers every 10 minutes light intensity for several years. If I retrieve the logger, I can download the information and determine on every date daylength and start of the day. The daylength tells me the northern latitude (as long as the bird is not above the arctic circle) and the start of day shows the longitude (time of sunrise). The location is accurate on 200 km, but with these birds which migrate 3000 km, this is accurate enough. The good thing is that they are light weight and cheap compared to other techniques.

The loggers are attached to white leg rings with red inscription which are placed over the metal ring. So the logger is an extra ring, which I can easily remove and replace. The other plastic ring with inscription is a kind of name tag. Colour and inscription together are uniuqe for every individual an can be read with a telescope from 200 m distance.

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