What's Happening?
This robin is all wet! He's just had a bath, and this is part of the process. Why?

Robins bathe partly to get their feathers wet and clean, but also to get their skin wet and clean. They have to fluff up the feathers to let water through to their skin. Then they shake to get the water off.

Look closley and you'll see that even where his feathers on the outside are bright red, the downy feathers underneath are gray.  Many of the red feathers are just red at the tip, and the part in front is gray. Look at the tail feathers; when they get very wet they get stringy. He needs to shake out and then preen out all the water so each feather can be the right shape again. His tail helps him steer in flight. If a predator came right now, he could fly away, but not as well as when he’s nice and dry. Robins are very careful about taking a bath. They bathe only in places where they feel very safe. —Laura Erickson

Courtesy Randy Indish