Sea Gulls Flying Over the Water of San Francisco Bay. Here you are on the deck of a ferryboat that is crossing San Francisco Harbor. Do you know another place where ferryboats cross a harbor? See the sea gulls that are following the boat. The boat has left a foamy track on the water that is called the wake. Do you know why the gulls are following the boat? They are looking for something to eat. They can live on the fish they catch but they have learned to like our food, too. Sea gulls are very strong birds. They can fly for days without resting. They are beautiful to watch as they fly, or swoop down to skim something from the water. But they are very noisy, too.Gulls make their nests of grass, moss and seaweed on rocky cliffs. Their eggs are light brownish spotted with chocolate color. They do not hatch more than three in one brood.