Herring Gulls doing a riverdance.
Actually this is worm charming or "puddling". Worms breath through their skin which has to be wet. When it rains they know they can come to the surface and move to new locations or mate. Seagulls have learnt to imitate the sound of raindrops and bring worms to the surface so they can eat them. Some people think the worms come up so they don't drown. This can't be correct because worms can survive for weeks under water so long as there is enough oxygen in the water.

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