The tag you see on this bird's leg weighs 0.4 grams or less than a paper clip—light enough that the bird (a dunlin in Chukotka, Russia) will be able to fly off on its seasonal migration with the tag attached.
For Rebecca Bentzen of the WCS Arctic Beringia Program, this is invaluable. To date, little is known about the Russian dunlin's winter travels, though that info would be a boost in figuring out how to protect it.
These tags will help shed light on the mystery. They record the level of sunlight in relation to an internal timer. From these readings, Bentzen can figure out roughly where the bird was each day—sunrise and sunset times, plus solar midday, suggest a latitude and longitude.
The trick is retrieving the data. The tags can't transmit it on their own, so Bentzen and the team must re-catch the birds upon their return to the north.
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