On the east coast, Herring gulls are widely known for droping clams,
mussels and other shellfish onto hard surfaces to break them. In fact, this
behavior has become a nusiance at parking lots in some port towns in New
England. I remember one town in my youth where people painted gulls on the
pavement in their parking lots, in the hopes that flying gulls would think
there was one on the ground already and not try to drop their meal too
close to its waiting beak. As I recall it sometimes worked, but the gulls
seemed to catch on after a while.

John Chapman
ragweed at igc.org
Seattle