Most of the birds that occur at Johnston are seabirds. Seabirds obtain their food from the sea and generally possess webbed feet and beaks adapted for feeding on fish and squid. They also have characteristic internal salt glands that make it possible for them to drink sea water. Long narrow wings efficient for soaring are found in many species. Seabirds are among the longest lived birds in the world, and life spans in excess of 30 years are not uncommon for some species.
Many seabirds mate for life, and both males and females incubate, brood, and feed their young.
Seabirds evolved on islands where natural predators were absent, therefore, they lack a well developed fear of people or predators. Their long lives and the ease with which the chicks and adults can be captured for banding and marking make them ideal subjects for long term studies. Seabird population numbers and movements can quickly reflect changes in the ocean environment. Other migratory birds occurring at Johnston Atoll include species that breed in Alaska, Canada, the mainland United States, and Asia, and migrate to the South and Central Pacific for the winter. These include many shorebirds and occasional waterfowl, hawks. owls, and egrets.