Birds that go underwater to catch fish are equipped with special adaptations that allow them to dive below the water’s surface and swim effectively. While most birds obtain their food from terrestrial sources, a handful of species have evolved for an aquatic lifestyle. Their streamlined bodies, waterproof feathers, and expert swimming skills enable them to pursue and capture prey underwater.
Diving Birds with Webbed Feet
Many diving birds have webbed feet which provide propulsion and steering underwater. Their toes are connected by membranes of skin called webbing. When the bird spreads its toes, the webs expand allowing the feet to push more water. This provides thrust to propel the bird through the water when diving in pursuit of fish.
Birds that use their webbed feet for underwater propulsion include:
- Cormorants
- Mergansers
- Loons
- Grebes
- Auks
- Anhingas
Cormorants are among the most adept fish-catching birds with fully webbed feet. They can dive to depths over 30 feet to snatch up prey. When they resurface, cormorants often swim with just their neck and head above water, using their webbed feet for propulsion. Their wettable feathers and ability to spread their wings to dry enables cormorants to make repeated dives.
Loons and Grebes
Loons and grebes are both diving bird families equipped with lobed webbed feet set far back on their bodies to make excellent swimmers. A loon’s webbing allows it to essentially paddle through the water when pursuing fish. Grebes have unusual rotating legs that provide even more thrust underwater. When paired with their streamlined bodies, loons and grebes can dive to impressive depths in excess of 100 feet.
Mergansers
Mergansers are diving ducks common on rivers and lakes. Their long, slender serrated bills are effective tools for grasping slippery fish. While their feet are not fully webbed, they have enough webbing to propel them underwater. They typically forage in small groups and can catch several small fish in a single dive.
Birds with Powerful Wings for Diving
While webbed feet provide the main source of propulsion for some diving birds, others rely more heavily on their wings. Their wings enable them to essentially fly or propel through the water when pursuing fish.
Examples of strong winged diving birds are:
- Gannets
- Terns
- Skimmers
- Boobies
Gannets
Gannets are large seabirds with pointed wings and streamlined bodies adapted for diving at high speeds. They plunge into the ocean from heights up to 100 feet to catch fish swimming near the surface. Right before impact, gannets extend their pointed wings to control the dive. Their air-filled bodies provide buoyancy to help them resurface.
Terns and Skimmers
Terns and skimmers have long, narrow wings tailored for making aerial acrobatic dives into water to catch small fish. Unlike gannets, they do not dive from great heights, but will rapidly plunge into the ocean from a hovering position. Their angular wings provide lift and maneuverability allowing terns and skimmers to dip repeatedly into the water’s surface to snatch prey.
Seabirds with Specialized Hunting Techniques
Some remarkable seabirds have developed highly specialized hunting techniques to catch fish underwater. While not all use their wings or feet to dive, they have evolved unique methods to snag slippery prey.
Pelicans
Pelicans are most famous for stealthily gliding over the water’s surface and scooping fish into their elastic throat pouches. Although their webbed feet are not involved directly in catching fish, pelicans use them to paddle and steer towards fish schools. Right before impact, they extend their pouches like dip nets to engulf fish and water.
Frigatebirds
Frigatebirds are masters of aerial piracy, forcing other birds to regurgitate their catches, then swooping to catch the dropped fish mid-air before they hit the water. Some also dive directly for fish, stabbing their sharp beaks into the water to impale prey. Their angular wings provide agility and speed for their pirating strategy.
Tropicbirds
Tropicbirds capture prey by hovering briefly over the ocean, then sharply plunging headfirst to seize fish with their dagger-like beaks. Their elongated central tail feathers give them superior aerial maneuverability and balance when dipping into the water.
Plunge Diving Birds
Many diving bird species use a technique called plunge diving to catch fish. It involves soaring high up then folding their wings back to plummet down, piercing the water’s surface. Just before impact, they extend their wings or feet to brake and control the dive.
Plunge divers include:
- Gannets
- Terns
- Skimmers
- Pelicans
- Boobies
- Tropicbirds
Gannets and boobies are classic plunge divers, achieving tremendous speeds when free falling from heights over 100 feet. Just before hitting the water, they angle their aerodynamic bodies to stab deep beneath the surface.
Terns, skimmers and tropicbirds plunge from much lower heights, using their angular, pointed wings to slice cleanly into the water to grab small fish near the surface. Pelicans plunge with their pouches spread wide to engulf fish schools in one scoop.
Pursuit Diving Birds
Pursuit diving describes the technique where birds swim underwater to chase moving fish. Their streamlined shape, propulsive feet or wings allow them to effectively swim after speedy prey.
Pursuit divers include:
- Cormorants
- Mergansers
- Loons
- Grebes
- Auks
- Anhingas
Cormorants, loons, grebes and mergansers all use their powerful webbed feet to drive them through the water when pursuing fish. Auks flap their stunted wings underwater to dive as deep as 200 feet in pursuit of prey. Anhingas combine wing flapping with webbed feet paddling to swiftly chase fish under the water.
Surface Diving Birds
Many diving birds specialize in catching prey near the water’s surface. Rather than plunging to depth, they dip just their head or neck into the water to grab fish.
Surface divers include:
- Herons
- Kingfishers
- Terns
- Skimmers
- Frigatebirds
- Tropicbirds
Herons and kingfishers wade patiently in shallow water waiting to spear fish that come near. Terns and skimmers fly just over the surface then briefly dip their beaks to nab small fish. Frigatebirds and tropicbirds stab down with lightning speed to impale prey.
These hunting methods allow surface divers to conserve energy compared to deep diving birds. They minimize time underwater where swimming is more effortful.
Diving Bird Adaptations
Birds that regularly dive underwater to catch fish have evolved a number of key adaptations to their bodies and feathers.
Streamlined Bodies
Diving birds tend to have long, narrow bodies that reduce drag and allow them to swim swiftly underwater. Their wings are more pointed and their necks elongated. This profile cuts smoothly through the water when diving in pursuit of fish.
Waterproof Plumage
Birds that dive have waterproof feathers coated in oils that prevent water from penetrating to their skin. This allows them to stay warm and buoyant even after spending extended time in cold water. Their outer contour feathers are stiff and tightly interlocked to shield the more downy insulating layer.
Salt Glands
Marine diving birds have special glands near their eyes that filter excess salt from their bloodstream. This enables them to drink seawater and stay hydrated without disrupting their body’s salt balance.
Air Sacs
Many diving birds have air sacs throughout their bodies and bones that help provide buoyancy underwater. Air sacs in the neck and chest create internal flotation devices.
Short Legs
To reduce drag while swimming, diving birds have shorter legs set further back on their bodies. Their feet tend to be enlarged or webbed which improves propulsion.
Notable Diving Bird Species
Here are some of the most impressive fish-catching birds with adaptations that allow them to dive and swim underwater:
Cormorants
- Fully webbed feet provide propulsion when diving
- Wettable feathers help shed water
- Hooked bills grasp slippery fish
- Can dive to depths over 30 feet
Loons
- Feet placed far back act like paddles
- Solid bones aid in diving
- Streamlined shape for swimming
- Able to dive over 100 feet deep
Auks
- Wings adapted for underwater flying
- Can dive 200 feet to pursue fish
- Legs set far back for swimming
- Bills with cross-grooves help grasp prey
Gannets
- Pointed wings hit water with force
- Air sacs provide internal buoyancy
- Nostrils seal automatically when diving
- Plunge from heights up to 100 feet
Pelicans
- Hinged throat pouch acts as a scoop
- Pouch holds up to 3 gallons of fish
- Webbed feet used to steer towards fish
- Plunge with pouch fully expanded
Threats Facing Diving Birds
Although well adapted for their specialized hunting strategy, many diving bird populations face serious threats to their survival. Some key perils include:
- Habitat degradation – Loss of wetlands reduces food availability
- Pollution – Contaminants concentrate up the food chain
- Overfishing – Reduces food supplies for piscivorous birds
- Climate change – Rising sea levels threaten nesting sites
- Extreme weather – Hurricanes and storms can devastate colonies
- Oil spills – Plumage soiled with oil destroys insulation
Conservation efforts aimed at protecting wetlands, managing fisheries sustainably and reducing pollution can help safeguard diving bird populations into the future.
Conclusion
Diving underwater in pursuit of fish requires specialized adaptations. Birds with webbed feet, streamlined bodies, waterproof feathers and other modifications are equipped for this unique hunting strategy. Plunge divers, pursuit divers and surface divers use different techniques to catch aquatic prey. Learning more about how birds are so exceptionally adapted for swimming underwater reveals nature’s ingenuity at work.