Grey herons need to be meticulous cleaners in order to keep their plumage in prime condition. After feeding on eels and other fish, when their heads and necks have been coated with sticky slime, they rub the affected feathers on their patches of powder-down - modified feathers that break down into fine powder. The powder-down soaks up the slime, and the birds can then scrape off the deposit of slime and powder using a special comb-like claw.