Flightlessness in birds has evolved independently multiple times across various lineages. While the causes are not fully understood, flightlessness is thought to arise due to isolation on islands with a lack of ground predators or hunting ability combined with abundant food sources.
There are numerous examples of ratite birds and waterfowl that have evolved flightlessness. Here we explore some of the diverse species of flightless birds found around the world.
Ratites
Ratites are a group of large, flightless birds including ostriches, emus, cassowaries, rheas, and kiwis. They share a common ancestor and are different from flying birds in several aspects of their anatomy. Their sternum lacks a keel to anchor flight muscles and their wings are vestigial. Their feathers also lack barbs, having a more hair-like form.
While they can’t fly, ratites are very adept runners. They use their powerful legs to escape predators and have specialized feet well-adapted to the environment where they live.
Ostrich
The ostrich (Struthio camelus) is the largest and heaviest living bird, native to the savannas and deserts of Africa. An adult male can reach 9 feet tall and weigh over 300 pounds. Ostriches are unable to fly but are specialized runners, with long and powerful legs that help them sprint up to 43 miles per hour – the fastest land speed of any bird.
Their wings are used for balance during running and courtship displays. Ostriches have distinctive black and white plumage on their body, with bare grayish-pink skin on their legs and neck.
They have excellent eyesight and hearing to detect threats on the open grasslands. Ostriches are omnivorous, feeding on seeds, roots, grasses, insects, lizards, and sometimes small mammals or birds.
Want to read more about the ostrich? Read: What Eats An Ostrich?
Emu
The emu (Dromaius novaehollandiae) is the second largest living bird after the ostrich, found across most of mainland Australia. Emus can reach 6 feet tall and weigh nearly 100 pounds.
They share several similarities with ostriches – they are flightless, mostly black and brown in color with bare blue skin on their head and neck, and have small vestigial wings used mainly for balance when running.
Emus are very quick on their feet, running at speeds up to 30 miles per hour. They have three large toes which help in running over tough rocky and desert terrain. Emus are omnivorous but mostly eat grasses, fruits, flowers, seeds, and insects foraging from the ground.
Cassowary
Cassowaries encompass several species of large flightless birds that inhabit the dense rainforests of New Guinea, northeastern Australia, and nearby islands. The southern cassowary (Casuarius casuarius) is the third largest bird in the world after the ostrich and emu, growing up to 5.5 feet tall.
Their black plumage features a striking blue face and neck, and a prominent head casque or crest made of keratin. Cassowaries are skilled runners but also excellent swimmers and jumpers.
They have sharp claws on three toes that can serve as weapons against predators or threats. Cassowaries are frugivorous, mainly eating fallen fruits and assisting in seed dispersal through the rainforest.
Rhea
Rheas are large, flightless birds native to open grasslands, savannas, and scrublands of South America, found primarily in Argentina and Brazil. The greater rhea (Rhea americana) can reach 5 feet tall and weigh nearly 60 pounds.
Rheas are known for their gray-brown plumage and long legs and neck which allow them to easily see over tall grass while foraging. They use their small vestigial wings for balance when running, which they can do at speeds of nearly 40 miles per hour over sustained stretches.
Rheas are omnivores feeding on plant matter as well as insects, small vertebrates, and eggs stolen from nests.
Kiwi
The kiwi comprises several species of small, completely flightless birds native to New Zealand. They are the smallest members of the ratite group. Kiwi species including the great spotted kiwi (Apteryx haastii) grow to around 20 inches tall and weigh 6-9 pounds.
They have brown plumage streaked with gray and reddish-brown, large claws on their feet, prominent whiskers on their face, and a very long slender bill which they use to probe the soil and detect prey like worms and insects.
Kiwi are nocturnal and have a highly developed sense of smell, unusual for birds. They also have the largest egg-to-body ratio of any bird. Kiwi remains extremely vulnerable to introduced predatory mammals and habitat loss.
Other Unique Flightless Birds
Beyond ratites, there are numerous other examples of birds that have evolved flightlessness, often inhabiting isolated island habitats. These include several species of rails, grebes, teals, cormorants, parrots, and more.
Kākāpō
The kākāpō (Strigops habroptilus) is a large, nocturnal, flightless parrot endemic to New Zealand. It is the world’s only flightless parrot and also the heaviest parrot. Adults can reach up to 4 pounds in weight and 30 inches in length. They have soft greenish-yellow feathers streaked with black and brown for camouflage in the forest environment where they live.
As a defense mechanism, kākāpō freeze motionless rather than fleeing from predators. They are herbivores and have a strong odor that males emit as part of mating displays. Once widespread in New Zealand, predation and habitat loss led kākāpō to the brink of extinction with only around 200 remaining today through intensive conservation efforts.
Weka
Wekas belong to several species of rail endemic to New Zealand’s forests and scrublands, including the buff weka (Gallirallus australis) and North Island weka (Gallirallus greyii). Wekas measure 20-25 inches long and weigh between 1-4 pounds. Their grey-brown and black feather patterns provide camouflage in the forest understory but wekas have lost the ability for sustained flight and only make short fluttering flights.
Wekas are generalist feeders, consuming fruit, seeds, and foliage as well as insect, amphibians, carrion, and scraps. They are very inquisitive birds known for boldly approaching humans, cars, and buildings out of curiosity.
Takahe
The takahe (Porphyrio hochstetteri) is a large, mostly flightless rail native to the alpine grasslands of New Zealand which was thought extinct for several decades but rediscovered in 1948. It has beautiful blue and green plumage and can grow 20-26 inches long weighing 7-10 pounds.
The takahe has small vestigial wings but is incapable of prolonged flight, serving mainly for display and balance. It has a large sturdy bill for grazing grasses, herbs, and mosses in its mountain habitat. Takahe forms monogamous pairs for life with both parents sharing incubation duties.
After near extinction from hunting and predation, takahe has been relocated to predator-free island sanctuaries with stabilized populations of around 300 birds.
Great Bustard
The great bustard (Otis tarda) of Europe and Central Asia represents the heaviest living flying bird but is a poor flier, spending most of its time walking the grasslands. Males can reach nearly 4 feet long and weigh over 40 pounds.
They have long gray feathers helping provide camouflage amongst rocks and brush where they reside. Great bustards are omnivorous, feeding on leaves, seeds, insects, and even small mammals and reptiles.
These solitary birds hide their nests on the ground which combined with collisions with power lines and hunting lead to their threatened conservation status.
Steamer Duck
Steamer ducks are a genus (Tachyeres) of ducks native to South America comprised of four living species, three of which have adaptations for wing-propelled diving and flightlessness associated with their marine habitat. The most widespread is the Magellanic flightless steamer duck (Tachyeres pteneres) found along the southern coast of Chile and Argentina.
Growing nearly 2 feet long and 10 pounds, steamer ducks use their wings for swimming underwater but lost aerial flight capability. Their legs set far back on the body are used for pushing off from land into the ocean where they feed on mollusks and other marine invertebrates.
Female steamer ducks have grey and white plumage compared to black males. They are aggressive territorial birds known for attacking intruders with slashes from bony wing spurs.
Rail
The rail family (Rallidae) encompasses a diverse range of mid-sized, terrestrial birds distributed globally that have adapted to aquatic, forest, and grassland habitats. Many islands have species of flightless rails like the Guam Rail (Gallirallus owstoni) and Lord Howe Woodhen (Gallirallus sylvestris) which lost the ability for sustained flight in the absence of predators.
These rails have short rounded wings, large feet adapted to terrestrial mobility, a slim profile to pass through dense vegetation, and variable plumage patterns to camouflage in their habitats.
Most rails feed on an omnivorous diet opportunistically eating aquatic vegetation and invertebrates, insects, seeds, and fruits. The vulnerability of island rails to habitat loss and invasive species has left over 90 extinct species and many others threatened.
Great Auk
The great auk (Pinguinus impennis) was a flightless seabird that became extinct in the mid-19th century due to overhunting for its down feathers and meat. It bred on rocky islands across the frigid North Atlantic.
Standing about 30 inches tall and weighing 11 pounds, the black and white great auk was related to modern penguins but could only flap its small wings to swim underwater. It spent the most time on land digesting its food from fish captured during diving. Great auks were defenseless against human hunters at their island nesting sites.
The last known great auks were killed in 1844 at Eldey Island off Iceland, ending a lineage that evolved flightlessness nearly 75 million years ago. Today it serves as a sobering lesson about species vulnerability to extinction due to over exploitation.
Tasmanian Native-hen
The Tasmanian native-hen or Tasmanian native-hen (Tribonyx mortierii) is another flightless rail, found today only on the island of Tasmania off Australia’s southeastern coast. Growing 12-15 inches long, it has a black plumage set off by a bright blue stripe along its wing as well as red legs and red coloring around its eyes.
Tasmanian native-hens forage in wetlands and grasslands for plant shoots, bulbs, seeds, insects, spiders, and worms. They lost the ability for long-distance flight as Tasmania lacked terrestrial predators.
Native-hen numbers declined with habitat loss and predation by introduced species. Conservation measures and predator control have assisted populations to rebound over the last decades.
Inaccessible Island Rail
The Inaccessible Island Rail (Atlantisia rogersi) is the smallest living flightless bird in the world, found only on the aptly named Inaccessible Island, a small volcanic island in the South Atlantic Ocean.
It occupies grasslands and marshes of this predator-free island refuge located west of Africa measures only 13 centimeters or 5 inches long and weighs around 34 grams. Dark grey and brown plumage blends into the tussock grass habitat where it lives.
The diet and behavior of this elusive and tiny rail remain largely unknown but are thought to consist of invertebrates and possibly even plant material. Without major threats, Inaccessible Island Rail persists on its remote island home.
Rüppell’s Vulture
Rüppell’s vulture (Gyps rueppelli) resides in the Sahel region of central Africa and has several adaptations for a soaring and gliding lifestyle rather than powered flight. With a 6-foot wingspan, adults can weigh up to 20 pounds.
The adaptations allowing extensive periods gliding over the arid grasslands in search of its carrion meals include fused vertebrae and wing anatomy that minimize energy expenditure, up to a 10-foot wingspan, and a lightweight skeleton comprising just 7% of its body weight.
Rüppell’s vulture spends over 95% of its flight time soaring without wing flapping. Its size and adaptations provide excellent thermal soaring and gliding ability with minimal need for powered flight.
North Island Brown Kiwi
The brown kiwi comprises four species found across various habitats in New Zealand. The North Island Brown Kiwi (Apteryx mantelli) occurs widely in the Northland, Coromandel Peninsula, and eastern regions but faced declining populations over recent decades due to predation, habitat loss, and fragmentation.
Weighing 3-8 pounds as an adult, it is streaked reddish-brown in color with a long pale bill with nostrils at the tip used to probe soil and detect earthworm prey. With a strong sense of smell and whiskers around its bill, the long-lived North Island Brown Kiwi is a mostly nocturnal forager.
Without flight capabilities, populations remain vulnerable to non-native predators though conservation management has aided recovery in some regions.
Flightless Cormorant
The flightless cormorant (Phalacrocorax harrisi), also known as the Galapagos cormorant, is an endemic seabird found on the Galapagos Islands off Ecuador that lost aerial flight capability over evolutionary time.
Weighing around 5 pounds with a 30-inch length, it is the world’s largest of some 40 species of cormorants. adaptations for diving and swimming include fairly small wings relative to body size and robust legs set far back on the body to propel swimming.
Mostly black with variable orange facial patches, it dives to catch eels, octopuses, and other small aquatic prey. With no natural predators on the Galapagos Islands, the flightless cormorant was able to successfully adapt to an environment with abundant food.
Campbell Teal
The Campbell teal or Campbell Island teal (Anas nesiotis) is a small, mostly nocturnal, flightless dabbling duck endemic to Campbell and small neighboring islands south of New Zealand.
Weighing only 550 grams or 1.2 pounds fully grown with brown plumage for concealment among vegetation, the Campbell teal is both the smallest and only flightless duck in the world.
With no predators, it was able to diverge from its flying ancestors after arriving at these remote uninhabited islands and adapt as an ecological generalist at the islands’ shorelines and interior, breeding in tunnels, grazing, and feeding on invertebrates.
Conservation efforts including captive breeding have been made after habitat degradation by invasive mammals reduced their population.
Titicaca Grebe
The Titicaca flightless grebe or short-winged grebe (Rollandia microptera) resides solely around Lake Titicaca which sits 12,500 feet in elevation straddling the border of Bolivia and Peru. Weighing less than a pound but nearly a foot in length, they are slate grey in color for camouflage around the reedy shorelines of South America’s largest lake.
Over evolutionary time isolation in the high altitude habitat of Lake Titicaca with plentiful food and an absence of predators led the grebe’s wings to greatly reduce in size where they serve mainly for display purposes.
Titicaca grebes dive to catch small fish and nest on floating reed beds. While still common on the lake, conservation concern exists due to pollution and habitat disturbance.
Guam Rail
The Guam rail (Gallirallus owstoni) is a medium-sized, flightless rail endemic to the island of Guam. It has chestnut feathers, white spots, a blue-colored bill, red eyes, and a grey head.
Growing 8 to 12 inches and weighing around 10 oz., its wings became vestigial as Guam had no native mammalian predators. The species used to be abundant in forest and scrubland habitats of Guam until the accidental introduction of the invasive brown tree snake devastated the population which plummeted to less than 100 by the 1980s.
Control programs limit snakes and some Guam rails have been relocated to snake-free islands for population recovery. Locally it goes by the name Ko’ko’.
Conclusion
In this article, we covered a broad diversity of flightless bird species around the world ranging from the large running ratites of Africa, Australia, and South America to numerous island rails, grebes, ducks, cormorants, and other uniquely adapted species including some now sadly extinct.
While flight provides huge advantages, these species thrived without it through habitat isolation and lack of predators. Yet many now face substantial threats from human activity and serve as important reminders of our role in species conservation. The persistence of flightless birds also continues to fascinate biologists studying the evolutionary mechanisms underlying lost flight capabilities.
