Some birds can navigate and hunt beneath the water’s surface. A specialized group has evolved unique adaptations to thrive in aquatic environments, demonstrating diverse ways they interact with the underwater world.
Birds That Dive and Swim
Numerous bird species are adept at diving and swimming, utilizing different methods for propulsion underwater.
Penguins are flightless birds that propel themselves using powerful, wing-like flippers, effectively “flying” through the water. Their streamlined bodies reduce drag, allowing remarkable speed. Cormorants are another group known for their diving prowess, primarily using large, webbed feet for propulsion, often with a burst-and-glide style. They can swim quickly and use their wings for steering.
Other diving birds include:
- Loons, which are foot-propelled divers with legs set far back on their bodies, aiding underwater maneuverability.
- Grebes, which rely on their feet for propulsion, possessing lobed toes that function like paddles.
- Diving ducks, such as mergansers and scaup, which use their large, webbed feet to drive them through the water. Some can also use their wings for additional propulsion.
- Auks, including puffins and murres, which are wing-propelled divers that “fly” underwater using short, stiff wings as powerful flippers.
Mastering the Underwater World: Specialized Adaptations
Birds that regularly venture underwater exhibit specialized adaptations, both structural and physiological, that facilitate their aquatic lifestyle.
Structurally, many diving birds have dense bones, unlike the hollow bones typical of most flying birds. This increased bone density reduces buoyancy, allowing them to submerge and remain underwater. Their bodies are often streamlined and torpedo-shaped, minimizing water resistance and enabling efficient movement. Webbed feet, or lobed toes, provide a broad surface area for powerful propulsion. Wings are also highly adapted; in penguins, they have evolved into rigid flippers, while auks have short, stiff wings for “underwater flight,” allowing powerful thrust.
Physiologically, diving birds possess remarkable abilities to manage oxygen during dives. They can hold their breath for extended periods, and many can slow their heart rate, a phenomenon known as bradycardia. They also selectively shunt blood flow, directing oxygen-rich blood to vital organs like the brain and heart while reducing flow to less essential areas.
Feather structure and preen oil are significant adaptations. Diving birds have densely packed feathers, which they meticulously coat with oil from a specialized uropygial gland. This creates a waterproof barrier, insulating them and controlling buoyancy.
Some species, like cormorants, have less waterproof feathers, allowing them to become waterlogged for easier diving, which necessitates drying their wings after surfacing. Gannets have evolved specialized nostrils that close to prevent water entry during high-speed dives, and respiratory system extensions act as “airbags” to cushion impact. Their eyes are also adapted for underwater vision, sometimes changing lens shape to focus clearly.
Why Birds Go Beneath the Surface
The primary reasons birds venture underwater are linked to their survival and ecological roles.
Foraging for food is a major driver, with many species diving to catch fish, crustaceans, aquatic plants, and other invertebrates. Their underwater capabilities provide access to a rich food source unavailable to terrestrial or surface-feeding birds. For example, cormorants are expert fishers, diving to depths of 45 meters (150 feet) to pursue prey. Emperor penguins can dive over 560 meters (1,850 feet) for up to 20 minutes to find food like krill, fish, and squid.
Beyond feeding, going beneath the surface serves as a strategy for evading predators. By diving, birds can escape threats active above the water or on land, finding refuge. The ability to quickly submerge allows them to disappear from sight, making it difficult for predators to track them. This combination of efficient foraging and predator avoidance highlights how their specialized underwater adaptations contribute to their success in diverse aquatic habitats.