Pelicans are gregarious birds. They move along in long lines — sometimes in a single file and sometimes in a V formation. They feed by lining up across a lake or lagoon and advancing towards the shore, beating their wings and driving the fish up ahead of them into shallow waters. Pelicans have an impeccable sense of timing thanks to which they synchronise the time when they all dip their huge beaks into the water to net their prey. On islands and marshes, the females lay one to four eggs in a rough hollow in the ground to be incubated by both parents until they hatch four to five weeks later. Ornithologists have observed that pelicans even face the same direction while resting on land, unless disturbed by something! Their beaks are long, heavy, flattened and hooked at the tip. The pouch below the lower bill is used as a fish net and can hold up to three gallons of water. When it is hot, the birds vibrate the sagging skin of the pouch to cool themselves.