The Truth About Birds and Underwater Survival
No bird can breathe underwater using gills or other aquatic respiratory organs. Birds are air-breathing vertebrates, and their survival beneath the surface relies entirely on their ability to hold their breath. While some avian species are remarkably adept at navigating and foraging in aquatic environments, their time submerged is always limited by the oxygen supply they carry. They must eventually return to the surface to replenish oxygen stores.
Remarkable Adaptations for Submerged Life
Many birds have developed a suite of specialized physiological and anatomical features that enable them to thrive in aquatic environments, despite their reliance on atmospheric oxygen. One such adaptation involves their capacity for efficient oxygen use, where their blood and muscles contain high concentrations of myoglobin. This protein is similar to hemoglobin in blood but is found in muscle tissue, allowing for enhanced oxygen storage and delivery directly to working muscles during a dive. In conjunction with improved oxygen storage, diving birds exhibit bradycardia, a physiological response where their heart rate slows down during submersion. This conserves oxygen by decreasing metabolic demand.
Another crucial adaptation is peripheral vasoconstriction, a process where blood flow is redirected away from non-essential organs and tissues towards the heart, brain, and active muscles. This ensures that vital organs receive a continuous supply of oxygenated blood, prolonging dive times. Many diving birds also possess dense bones, which are heavier than the pneumatic bones found in most flying birds. This increased bone density helps reduce buoyancy, allowing them to submerge with less effort.
Beyond internal physiology, external features also play a significant role in their aquatic prowess. Specialized plumage is common among diving birds; some have dense, waterproof feathers that trap a layer of air, providing insulation and buoyancy control. Other species, like cormorants, have less waterproof feathers that become waterlogged, reducing buoyancy and allowing them to sink and swim efficiently. Furthermore, streamlined body shapes minimize drag, enabling them to move through water with speed and agility while pursuing prey.
Extreme Divers of the Avian World
The Emperor Penguin is among the most impressive avian divers, known for its extraordinary ability to undertake the deepest and longest dives. These Antarctic inhabitants can plunge to depths exceeding 500 meters (about 1,640 feet) and remain submerged for over 20 minutes.
The Common Loon, or Great Northern Diver, exemplifies a master of prolonged underwater pursuit, frequently observed diving for fish in freshwater lakes. These birds are foot-propelled divers, using their powerful legs positioned far back on their bodies to propel themselves through the water with precision and speed. Their bodies are highly streamlined, allowing for efficient movement as they chase their prey.
Cormorants are another group of highly adapted diving birds, frequently seen drying their wings after a dive. Unlike many aquatic birds, their feathers are not fully waterproof, which allows them to become saturated with water, reducing buoyancy and making it easier to dive deep and pursue fish. This unique feather structure, combined with powerful leg propulsion, makes them effective underwater hunters.
Puffins and Murres are striking examples of birds that “fly” underwater, using their wings for propulsion rather than their feet. Their short, powerful wings are adapted for both aerial flight and underwater maneuverability, allowing them to chase fish with remarkable agility. These species demonstrate how different evolutionary paths can lead to highly effective underwater locomotion in birds.
The Dipper, or Water Ouzel, stands out as a unique songbird that defies typical avian behavior by diving and walking along riverbeds in fast-flowing streams. This small bird plunges into cold water, using its strong feet to grip rocks and search for aquatic insects and larvae. Its ability to forage underwater in such challenging conditions highlights the diverse range of adaptations that allow some birds to exploit aquatic food sources.