A seabird can be defined as a bird that makes its living primarily from the ocean, beyond the intertidal or surf zone.

Seabirds are beautifully adapted for life in the ocean. Generally, they have dense, waterproof feathers; layers of fat; and a desalinization system to remove excess salt. Some, like the Common Murre, stick fairly close to home throughout their lives; others, like some albatrosses and shearwaters, literally wander around the much of the North Pacific over the course of a year. Their body shapes reflect their life histories:

• The stubby wings and potato-shaped body of the Marbled Murrelet are unsuitable for long-distance flying but great for pursuit diving underwater, giving them a three-dimensional feeding environment. This is the right design for colder, northerly waters where prey form dense schooling balls. 
• Conversely, the long, slim wings, relatively small body, and heightened sense of smell of the Laysan Albatross is perfect for long-distance flying to find scattered prey at the ocean’s surface. This is the right design for warmer, open-ocean waters where prey is more widely scattered at the surface.

Most seabirds are long-lived (some over 50 years) and don’t start to breed until they are 5-10 years old. These characteristics may be an evolutionary strategy to cope with their highly variable ocean environment: it gives birds a chance to spend several years learning how to find prey over many seasons before attempting breeding, and, gives adults many chances to successfully rear young who reach reproductive age themselves.

Seabirds play important roles in marine, intertidal, and terrestrial environments because they forage throughout the world’s oceans, consume an estimated 7% of marine productivity, and are a food source for other marine and terrestrial predators and humans. On land and near shore, seabird guano fertilizes terrestrial, intertidal and subtidal zones, enhancing local plant growth.