Mr. Purple Cat Esq. I dont remember ever actually seeing this but I felt compelled to look up the explanation..
they are causing vibrations to irritate the worms to the surface (it is possible that they respond to the vibrations because they are similar to those caused by rain, and the worms head upward to avoid drowning in their burrows).
This is nothing new, however - some species of gulls have likely been doing this for millenia. I think the issue here is that the name "seagull" is a misnomer - many gulls have nothing whatever to do with the sea. That's why they are properly known simply as gulls. There are species of gulls that nest inland in the north and forage on croplands without ever seeing the ocean.