What birds lost their ability to fly?

Some species of birds have lost the ability to fly over time through evolution. Flightlessness in birds has evolved independently multiple times for different reasons. The loss of flight can be traced to changes in the environment that made flying unnecessary, anatomical changes related to island habitats, or the absence of predators. While flightless birds are in the minority, there are at least 40 known species of flightless birds living today. Some of the more well-known flightless birds include ostriches, emus, rheas, cassowaries, kiwis, and penguins.

Main Flightless Bird Groups

Ratites

The ratites are a group of flightless birds that includes ostriches, emus, rheas, cassowaries, and kiwis. What these birds have in common is a flat, raft-like sternum or breastbone without the keel that anchors flight muscles in other birds. Unlike most other birds, ratites have small wings relative to their body size that cannot be used for flight. The living ratites evolved from flying ancestors that gave up aerial life tens of millions of years ago. Here is a breakdown of the major ratite groups:

Ostriches – Native to Africa, ostriches are the largest and fastest running birds in the world. They can grow up to 9 feet tall and weight over 300 pounds. Ostriches live in nomadic herds and use their speed, up to 43 mph, to escape predators.

Emus – Emus are the second largest living birds after ostriches. They are found in Australia where they travel great distances to find food and water. Emus can sprint up to 31 mph.

Rheas – Rheas resemble ostriches but are smaller in size. They live in open grasslands in South America. They can run at speeds approaching 40 mph.

Cassowaries – Cassowaries are large flightless birds that inhabit the tropical rainforests of New Guinea and northeastern Australia. They are an important part of the rainforest ecosystem, spreading seeds through digestion. Cassowaries are territorial and can use their sharp claws as weapons.

Kiwis – Kiwis are the smallest ratites and the national symbol of New Zealand. They are nocturnal birds that probe the ground with their long beaks searching for food. Kiwis play an important role in seed dispersal in the forest ecosystems where they live.

Pengins

Penguins are flightless seabirds found exclusively in the southern hemisphere. While they lost the ability to fly, penguins evolved for exceptional swimming skills using their flippers to propel through water. Their wings evolved into rigid flippers that penguins use to ‘fly’ underwater. There are 17 to 19 penguin species, depending on the classification. Some major penguin groups include:

Emperor Penguins – The largest penguin species, emperor penguins breed on the Antarctic ice where males incubate eggs. They can dive to depths of 1,500 feet searching for fish, krill, and squid.

King Penguins – The second largest penguin, king penguins breed on subantarctic islands. They can dive deeper than any other bird, reaching depths of 1,000 feet for up to 11 minutes.

Macaroni Penguins – Named for their showy yellow crest feathers, macaroni penguins breed in huge colonies on islands around Antarctica and southern South America.

Little Blue Penguins – The smallest penguin species, little blue penguins stand just over 1 foot tall. They are found on the coasts of New Zealand and southern Australia.

Flightless Cormorants

The flightless cormorant is the only cormorant species that lost the ability to fly. It lives exclusively on two remote islands in the Galapagos archipelago. With no natural predators, the flightless cormorant lost its flying ability over time. Its wings are about one-third the size needed to fly. The flightless cormorant dives underwater to catch fish.

Kagus

The kagu is a rare flightless bird that only lives in the forests of New Caledonia. It is the only surviving member of the Rhynochetidae family. The kagu has gray plumage and long crest feathers on its head. It spends most of its time on the ground foraging for food. The kagu is endangered with an estimated population between 250 to 1000 individuals in the wild.

Weak Flier Birds

Some birds are such weak fliers that they are essentially flightless except for brief flights. These weak fliers include:

Weka – A rail species found only in New Zealand. Wekas are almost completely flightless, only taking to the air when threatened.

Inaccessible Island Rail – This small rail inhabits Inaccessible Island, an isolated volcanic island in the southern Atlantic Ocean. It can only fly short distances.

Takahe – Another nearly flightless rail native to New Zealand. Takahes can only fly about 100 yards maximum.

Evolution of Flightlessness

Birds evolved from feathered dinosaurs over 150 million years ago. Powered flight allowed ancient birds to better evade predators, hunt prey, and disperse to new environments. For a few bird lineages, the evolutionary pressures to stay airborne were removed for different reasons:

Lack of Predators

On remote islands lacking predators, some birds gradually lost the ability to fly. With no predators to escape from by flying, the ability became unnecessary. Flight is metabolically and biomechanically costly, so flightlessness presented an evolutionary advantage in island habitats. The dodo is an extinct flightless bird that evolved on the island of Mauritius.

Abundant Food Resources

Some flightless bird species evolved on islands with abundant food sources and few predators. The abundant ground-based food made flight unnecessary for foraging. Birds adapted larger body sizes over time, which eventually made flight impossible. The elephant bird of Madagascar was an enormous flightless bird that weighed over 1,000 pounds. It evolved on an island with few predators and plentiful food.

New Ecological Opportunities

The evolution of flightlessness opened up new ecological opportunities for some birds. Ostriches, for example, specialized in running, which helped them thrive in open African savannas. Penguins lost flight but gained exceptional swimming skills that allow them to pursue fish underwater. These alternate evolutionary strategies proved successful in certain environments.

Anatomical Changes

As some flightless birds increased in size, their wing anatomy was disproportionally reduced, which eventually permanently eliminated flight capabilities. Changes included the reduction of the keel on the sternum as well as reduction of the wings. In penguins, the wings evolved into specialized flippers for swimming, making aerial flight impossible.

Facts About Flightless Birds

• There are around 40 species of flightless birds alive today.
• The ostrich is the largest living bird and can grow over 9 feet tall.
• Ostriches, emus, cassowaries, kiwis, and other ratites cannot fly.
• Penguins evolved for swimming and have rigid flippers instead of wings for flight.
• Most flightless birds are found in the Southern Hemisphere.
• New Zealand has many flightless birds, including the kiwi, weka, kakapo parrot, and takahe.
• The elephant bird of Madagascar, now extinct, was the largest bird ever at over 1,000 pounds.
• All flightless birds descend from flying ancestors.
• Flightlessness has evolved independently many different times in birds.
• Flight provides survival benefits; flightlessness evolves when those benefits disappear.

Flightless Birds By Region

Conclusion

While most birds take to the skies to fly, some peculiar bird species have become flightless over the course of evolution. Birds like ostriches, emus, penguins, kiwis, and cassowaries have adapted in ways that losing aerial locomotion provided evolutionary advantages. Flightlessness often evolves on islands with limited predators, abundant food resources, or new ecological opportunities. While flight provides immense survival benefits for birds, in certain environmental contexts, the ability to take to the air vanishes. The diversity of flightless birds reveals how dynamic evolution can be in producing adaptations to maximize survival.