This warbler isn't trying to grab the last seed in the jar – it's being weighed as part of a massive effort to track migrating birds by the British Trust for Ornithology.
Huge numbers of warblers, sand martins, house martins, swallows, nightjars and sparrowhawks roost at the private reserve in Rye, UK, where the project is under way. The site is one of the world's largest ringing stations: volunteers can put tags on up to a thousand bird ankles in one night.
After they've been logged, the birds are free to continue their migratory journey to Africa. Twitchers who spot a ringed bird can report it, helping researchers understand where birds travel and how long they live.
If you fancy more facts about our feathered friends, read about what it's like to be a bird and how birds took over the world.
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