Pelicans have a pouch on their lower bill which enables them to scoop up fish. The species most suited for diving to catch prey (such as cormorants and gannets) ingest stones that weight them down and help them plunge into the water more efficiently. They also have streamlined bodies and narrow nostrils (to prevent water from rushing in during a dive).
One intriguing species, the flightless cormorant, has adapted so well to diving that they have lost the ability to fly altogether. This species lives on the Galapagos Island where it is free from predators. The flightless cormorant dives for food using its webbed feet to propel itself through the water.