Gulls exist worldwide and breed on every continent, including Antarctica. Gulls are extremely intelligent, utilize a complex communication system and a highly developed social structure. These monogamous coastal/inland birds rarely venture far out to sea and usually return to the same colony year after year to breed. They are carnivores and may scavenge as well as take live food. Although some gulls are common, others are rare. In any case, the differences between gulls are often so subtle even experts find it hard to distinguish between them. Gulls are protected under the International Migratory Bird Treaty which was signed in 1918, making it one of the oldest wildlife protection laws in force.