Last week I saw two herring gulls on the grass in a town centre park. They were stamping their feed rapidly on the ground - were they worm charming and is this learned behaviour?
Yes they were, apparently the vibrations cause the worms to come to the surface, although I've never actually seen one be successful. IT would be an interesting project to watch them for an hour or two and count how many they actually eat. The behaviour would only be worthwhile if the gull gained more energy from the worm than the amount expended in stamping, although in winter it would probably be better than being stood still and losing heat anyway.
I don't hink I have seen young birds do it, only adults, so perhaps it takes them a while to pick it up from others.
Most, if not all Gulls do this, very amusing to watch, here's a gif I made of a Black-headed gull doing it at low tide - http://img.photobucket.com/albums/v111/joe47/Gullgif-2.gif