Gulls are known to use a variety of foraging techniques in a variety of habitats (Burger 1988). One behavior, referred to as “foot-paddling,” consists of rapidly alternating raising and lowering of the feet (Simmons 1961a). This behavior can be divided into two functions (Tinbergen 1962). First, on tidal mudflats, in pools of water, and on saturated sand, this behavior suspends sediment in water and creates quicksand, bringing buried invertebrates to the surface or inducing them to move so that they become visible. Second, foot-paddling on solid but moist grassy soil, hereafter referred to as terrestrial foot-paddling, is thought to induce earthworms to come to the surface in response to the vibrations in the soil (Tinbergen 1962, Edwards and Bohlen 1993; but see Sparks 1961).