Which bird can swim well but not fly in the sky?

There are a number of bird species that are excellent swimmers but incapable of true flight. While most birds take to the skies as their primary domain, some have evolved for an aquatic lifestyle, using their wings for swimming rather than flying. Their adaptations for swimming and diving come at the expense of aerial abilities. Let’s take a look at some of the prime examples of flightless swimming birds and what makes them unique.

Penguins

Penguins are the classic example of birds that swim instead of fly. There are 18 species of penguins, all restricted to the southern hemisphere. While penguins have wings, these wings have evolved into rigid flippers that propel them through the water. Their streamlined bodies, webbed feet, and efficient underwater movement make them superb swimmers and divers. However, their wings are useless for flight. Penguins use their flippers for propulsion in the water and for balancing when moving on land. Different penguin species are adapted for different aquatic lifestyles. The largest penguin, the Emperor Penguin, dives to depths of over 500 meters in search of fish and squid. Smaller crested penguins stay closer to the surface near krill swarms. When on land, penguins waddle and shuffle using their feet and tail. Their upright posture is another adaptation for swimming, allowing them to cut efficiently through the water. While penguins cannot fly, they do sometimes propel themselves out of the water and onto land or ice using their flippers. Overall, penguins are masters of swimming but the limitations of their wing anatomy leaves them flightless in the air.

Unique Features of Penguins

• Wings modified into rigid flippers for swimming propulsion
• Streamlined hydrodynamic body shape
• Dense waterproof feathers
• Powerful legs and webbed feet for swimming
• Upright posture when on land
• Ability to efficiently propel underwater
• Special adaptations in different species for deep diving or surface swimming

Loons

Loons are a group of 5 species of diving birds found primarily in cool northern regions of North America, Europe, and Asia. Known for their eerie, wavering calls, loons spend most of their time in the water diving to catch fish. Loons have solid bones which add weight and aid in diving. Their legs are set far back on their bodies, making them awkward on land but excellent for swimming. Loons have webbed feet and their pointy bills are perfect for spearing and holding onto slippery fish. When diving, loons use their feet for propulsion underwater. While loons are decent fliers, they have high wing-loading compared to birds of similar size which makes flying more energy intensive. Their small wings provide sufficient lift for migration and evading predators but aren’t efficient enough for extensive flight. Loons avoid taking off from land or water whenever possible, preferring to get airborne from downhill slopes or strong headwinds. Once airborne, loons have slow and labored flight with their neck and feet extended. They will fly low over the water and plop straight down onto the surface feet-first to land. Overall, loons are fare more specialized for swimming and diving than flying.

Unique Features of Loons

• Dense bones to aid in diving
• Legs set far back for swimming propulsion
• Webbed feet
• Sharp bill for catching fish
• Wings provide lift for short flights but inefficient for sustained flight
• Land and takeoff only when necessary

Cormorants

Cormorants are water birds found worldwide, often seen standing with wings spread out to dry. They are relatives of pelicans and frigatebirds. Cormorants have dense, wettable plumage which lacks the insulating quality of most birds. This allows their feathers to become thoroughly soaked, reducing buoyancy and enabling the cormorant to swim low in the water. Cormorants have partly webbed feet and their long, hooked bills are effective at snaring fish. Powerful legs and feet propel them through the water as they chase prey. Since their feathers lack waterproofing, cormorants spend a lot of time perching with wings spread to dry out. Cormorants nest in areas with good fishing nearby. They hunt by diving from the surface and pursuing fish underwater. Some species dive to significant depths. Cormorants fly well but their soaked wings require a lot of effort for takeoff. Their flight style has been described as labored and fluttering. Despite their adaptations for swimming after fish, cormorants have retained the ability for sustained flight to travel between feeding and nesting areas.

Unique Features of Cormorants

• Wettable plumage absorbs water
• No insulating feather layer
• Webbed feet
• Long hooked bill for catching fish
• Powerful legs propel them underwater
• Able to dive from surface and swim in pursuit of fish
• Flight capable but labored due to soaked wings

Grebes

Grebes are a family of small to medium sized diving birds with around 22 extant species. They inhabit freshwater wetlands worldwide. Grebes have several adaptations for an aquatic lifestyle. Their feet are lobed rather than webbed, with flaps of skin on each toe. While not as efficient as webbed feet for swimming, lobed feet provide better traction on vegetation near the water’s edge. Grebes are clumsy on land with legs placed far back on their bodies. However, they are very maneuverable in the water. Grebes have dense plumage and can compress their feathers to reduce buoyancy. Their wings are small but used similarly to penguins to propel underwater. Grebes hunt small fish, crustaceans, and insects either at the surface or while diving. To take flight, grebes will run across the water flapping their wings to become airborne. Once in the air they are capable fliers. Overall grebes are well adapted for swimming and diving but still retain the ability for flight at the cost of terrestrial abilities.

Unique Features of Grebes

• Lobed feet provide swimming propulsion and aid walking on vegetation
• Legs set far back on body
• Dense feathers can be compressed to reduce buoyancy while diving
• Small wings provide underwater propulsion
• Able to dive from surface or run along water before taking flight
• Capable sustained flight once airborne

Steamer Ducks

Steamer ducks are a genus (Tachyeres) containing 4 species endemic to South America. As their name suggests, they are a duck-like bird that is very well adapted to swimming but has lost the ability to fly. Unlike most ducks, steamer ducks use their wings underwater as steering rudders rather than for aerial flight. Their wings are short, broad, and leathery. Rows of stiff feather shafts along the trailing edges help the wings function as mobile diving planes. For propulsion, steamer ducks kick with their large webbed feet. On land they are quite clumsy, waddling and shuffling with wings tucked against their bodies. Their legs are set far back, an adaptation for foot-propelled swimming. When threatened on land, steamer ducks will flap their stubby wings and run across the water while slapping their feet on the surface until generating enough lift to become airborne. However, they are completely incapable of sustained flight and will crash land shortly after becoming briefly airborne. Of all swimming birds, steamer ducks are among the most flight handicapped.

Unique Features of Steamer Ducks

• Broad leathery wings for underwater steering
• Stiff feather rows act as movable keels
• Large webbed feet provide swimming propulsion
• Legs set far back on body
• Incapable of sustained flight
• Briefly airborne when flapping wings on water surface
• Use wings only for underwater steering

Great Cormorant

The Great Cormorant (Phalacrocorax carbo) is a large member of the cormorant family found across much of Europe, Asia, and parts of Africa. They are all-black with bright orange facial skin. Great Cormorants are highly aquatic and chase small fish by swimming and diving underwater. They use their large webbed feet for propulsion and have a long snakelike neck for quickly snatching prey. Their wettable plumage and denser bones aid in diving. Great Cormorants nest colonially on cliffs, trees, and artificial structures. They often perch with wings outstretched to dry. While primarily piscivorous, Great Cormorants are opportunistic foragers and sometimes feed on amphibians and crustaceans. They will migrate short distances between breeding colonies and feeding grounds. In flight, Great Cormorants have labored and fluttering wingbeats with neck and feet extended. They are capable fliers for migration but avoid extended flights and stay close to the water. Overall, Great Cormorants are highly specialized for foot-propelled diving and swimming after fish underwater. Their adaptations for an aquatic lifestyle have reduced their aerial abilities.

Flightless Cormorant

The Galapagos Flightless Cormorant (Phalacrocorax harrisi) is a unique cormorant endemic to the Galapagos Islands. As their name indicates, they have entirely lost the ability to fly. With no natural predators, swimming ability became more valuable than flight ability. The wings of Flightless Cormorants are one-third the size needed for flight. However, their feet are larger than other cormorants and fully webbed for superior swimming propulsion. Their feathers are thicker and more water repellent than other cormorants. They dive and swim to catch fish, crustaceans, and octopus. Since they cannot fly away, nesting colonies are always situated right next to feeding grounds. Rather than migrating, Flightless Cormorants disperse short distances by swimming and walking. This is one of the only southern hemisphere bird species to have lost the power of flight. The adaptation of high swimming and diving skill in the Galapagos environment rendered flight unnecessary over evolutionary time scales.

Unique Features of Flightless Cormorants

• Small stubby wings useless for flight
• Larger webbed feet provide swimming propulsion
• More waterproof plumage than other cormorants
• Live entirely near water’s edge
• Disperse locally by walking and swimming instead of flying

Flightless Birds – General Patterns

While the specific reasons for flightlessness vary across the examples discussed, some general trends emerge:

• All occupy islands or isolated habitat with reduced predation
• Swimming adaptations gain evolutionary priority over flight
• Wings become smaller and modified for swimming propulsion
• Enlarged feet provide improved propulsion through water
• Denser bones or plumage aid diving ability
• Bills adapt for fish/aquatic prey capture
• Legs located further back improve swimming stroke
• Perching or landing behaviors adapt in absence of flight

So in summary, birds that swim well while losing flight ability inhabit predator-free island situations. Their wings and feet take on new forms and functions for underwater propulsion rather than flying through air. Other structural adaptations enhance diving, swimming, and aquatic feeding. On land, their walking and perching habits also adapt to the loss of flight ability.

Conclusion

Penguins, loons, cormorants, grebes, steamer ducks, and the Flightless Cormorant represent examples of swimming specialized birds that have poor flying ability. All demonstrate convergent evolution toward foot-propelled diving and swimming underwater, along with other adaptations that improve aquatic feeding and movement. For these flightless swimming specialists, the ability to swim and dive supersedes the need or ability to fly effectively. Their lifestyle niches center around water rather than air. Losing aerial capabilities is not a disadvantage but rather allows improved swimming performance in the absence of flight predators. This reveals how birds can evolve in radical new directions when freed from the usual constraints of flight and dispersal. By extensively adapting for underwater swimming in place of flight, this unique group of birds shows the endless forms evolution can generate when ecological opportunity allows.