Many birds can swim, displaying diverse adaptations for aquatic environments. While some are highly specialized for life in and around water, others are not equipped for swimming and primarily inhabit terrestrial or aerial domains. This highlights the varied evolutionary paths birds have taken.
Birds Built for Water
Numerous bird species are well-suited for aquatic life, utilizing water for foraging, escape, or travel. Waterfowl, such as ducks, geese, and swans, commonly swim on the surface. Ducks include dabbling ducks, which tip to feed on underwater vegetation, and diving ducks, which fully submerge for prey like fish and mollusks.
Other proficient swimmers include penguins, flightless birds that spend much of their lives in the ocean, moving up to 25 miles per hour underwater. Loons and grebes are foot-propelled divers, using powerful legs and webbed or lobed feet to swim efficiently beneath the surface. Cormorants and anhingas also dive for fish, and some seabirds like puffins and auks use their wings to “fly” underwater. Pelicans use a plunge-diving technique, scooping fish in their large throat pouches.
Specialized Aquatic Adaptations
Aquatic birds exhibit specific physical features for movement and survival in water. Their feet often display webbing: palmate feet (ducks, gulls) have webbing between three front toes, while totipalmate feet (pelicans, cormorants) connect all four toes. Grebes have lobed feet, with each toe edged by skin lobes that expand and contract for propulsion. These foot structures act like paddles, enabling efficient movement.
Feather structure and maintenance are also important. Most water birds have a uropygial gland, or preen gland, near their tail base. This gland secretes an oily substance birds spread over feathers during preening, waterproofing the plumage. The intricate interlocking of feather barbs creates a tight barrier, preventing water penetration and keeping the bird dry and insulated.
Body shape and bone density are further adaptations. Many diving birds have streamlined bodies that reduce underwater drag. Unlike flying birds with hollow bones, some divers like loons and penguins have denser, solid bones, reducing buoyancy for deeper dives. Underwater hunters, such as cormorants and kingfishers, have specialized vision, including flexible lenses and a transparent nictitating membrane (third eyelid) that protects eyes and improves underwater clarity. Diving birds also exhibit physiological adaptations for breath-holding and oxygen management, with some species remaining submerged for extended periods.
Birds That Avoid Water
While many birds thrive in aquatic environments, a significant number are not adapted for swimming or deep-water immersion. Land birds, such as sparrows, robins, and eagles, lack specialized features for aquatic locomotion. These birds primarily forage and move on land or in the air. Raptors like eagles and owls may catch fish near the surface but do not dive deeply or swim extensively.
Birds not adapted for swimming often lack webbed feet, essential for water propulsion. Their feathers may also lack robust waterproofing, making them prone to waterlogging. The bone structure of many terrestrial and aerial birds is designed for lightweight flight, making them too buoyant for sustained underwater activity. These birds might wade in shallow water to drink or bathe, but their physiology is not suited for swimming or diving.