Black-headed gulls paddling

I've written about foot-paddling for worms on wet grass in Herring Gulls and Common Gulls in this blog before. My local park has flooded in the last few weeks and Black-headed Gulls have moved in, enjoying the flushes, which bring up a lot of worms. Black-headed Gulls foot-paddle in water, but apparently they don't do it on wet grass like other gulls (but see the clips by Ralph Hancock in the comments). In an article on foot paddling in gulls Niko Tinbergen speculated that the reason could be that Black-headed gulls are not heavy enough to produce the vibrations on the ground that stimulate the migration of worms to the surface.
I had never seen Black-headed Gulls paddling on water before. This morning there were at least 30 Black-headed gulls and I noticed a one briefly paddling on shallow water, and checking in front of its feet. A young gull came along and when at the same spot it started paddling too. I managed a short clip of it.

After a while one of the young ones got a worm, unclear if due to the paddling. Walking around the pools on areas where the gulls don't go by the road it was apparent that there were a lot of dead (drowned?) worms. I think that's what the gulls are after in the flood. The Herring gulls were also energetically pulling grass and leaves and soil from the shallow puddles to expose food.

More information
Tinbergen, N. Foot-paddling in gulls. Br. Birds 55, 117 (1962)