Seabirds are birds that have adapted to live in or near a saltwater environment. While they range in size, lifestyle, and even general appearance, all seabirds depend upon the ocean or sea for part or all of their livelihood. In general, seabirds live longer, breed later and have fewer young than other birds do, but they invest a great deal of time in their young. Most species nest in colonies, which can vary in size from a few dozen birds to millions.