Seagulls do a rain “dance” to bring earthworms to the surface so they can easily eat them. By stomping their feet on grassy areas, they create vibrations which are similar to that created by rain, which tricks the earthworms. – WTF Fun Facts
Source: http://animalbehaviouraberdeen.blogspot.com/2011/03/seagull-rain-dance.html
Very smart birds!