Wings are a defining characteristic of birds. They allow birds to fly and soar through the skies. However, not all birds can fly. There are several flightless bird species that have either small non-functional wings or no wings at all.
Flightless Birds With Reduced or Absent Wings
Here are some examples of flightless bird species with reduced or absent wings:
- Ostriches – The largest living birds. They are flightless and have small, vestigial wings.
- Cassowaries – Large flightless birds found in New Guinea and northeastern Australia. They have small stub-like wings with 5-6 quills.
- Kiwis – New Zealand’s national symbol. They are the smallest ratites with no visible wing structure and hidden vestigial wings.
- Emus – The second largest living birds after ostriches. Native to Australia. They have small stubby wings.
- Penguins – Flightless seabirds with flippers instead of wings. Their wings have evolved for swimming and diving.
- Kakapo – The heaviest parrot and the only flightless parrot. It is critically endangered with reduced stubby wings.
These birds have evolved over time to lose their ability to fly. In the absence of predators and need to fly to find food, wings became unnecessary. Their wings gradually reduced in size and functionality as an adaptation to their environment.
Reasons Why These Flightless Birds Lost Their Wings
There are several evolutionary reasons why these flightless birds have lost or reduced their wings:
- Lack of predators – On remote islands with no natural predators, the ability to escape by flying was not needed.
- Abundant food source – Plentiful food on the ground removed the need to fly in search of food.
- Energy conservation – Flying expends huge amounts of energy. Losing flight allowed conservation of energy.
- Environmental adaptation – Wings were disadvantageous in dense forests (kiwi), cold weather (penguin), or rugged terrain (cassowary).
With the evolutionary pressures that favor flight removed, maintaining large functional wings was energetically costly with no real benefit for these species. Over many generations, their wings disappeared or were greatly reduced as an adaptation to their ecological niches.
Vestigial Wings in Flightless Birds
Most flightless birds still retain vestigial wings or wing bones despite being unable to fly:
- Ostriches have small flap-like wings used for balance, courtship displays, and brooding eggs.
- Cassowaries have tiny wings with claws that are used for balance and shading eggs.
- Emus have small wings that assist with balance and heat regulation.
- Penguins’ wings have evolved into specialized flippers for swimming and diving.
- Kiwis have two hidden vestigial wings that are barely detectable underneath their feathers.
These vestigial wings had an aerodynamic function for their ancestors, but have lost most of their functionality due to disuse over many generations. They do, however, still play limited roles in display, balance, sheltering eggs, heat regulation etc.
Examples of Truly Wingless Birds
Most flightless birds have small non-functional wings or wing vestiges. However, a few rare bird species are truly wingless, lacking any visible wing structure:
- Inaccessible Island Rail – A small rail found only on Inaccessible Island in the South Atlantic. It is the only truly wingless bird alive today.
- Upland Moa – An extinct large moa species that lived in New Zealand. It had no wings or wing bones.
- Elephant Birds – Giant extinct flightless birds that lived in Madagascar. Some species were completely wingless.
These birds inhabit(ed) extremely isolated islands free of predators. With no need to fly or even glide, their wings gradually disappeared entirely through natural selection.
Inaccessible Island Rail
The Inaccessible Island Rail (Atlantisia rogersi) is the only living wingless bird species on Earth today. It is endemic to Inaccessible Island, a small volcanic island in the South Atlantic Ocean. This bird is flightless and has completely lost its wings as an adaptation to its predator-free habitat:
- About the size of a chicken and weighs around 350 g.
- Has a typical rail-like appearance with a slender body, laterally compressed tail, and strong legs and feet.
- Colored grey-brown above and dark grey below.
- Possesses no wings or wing bones whatsoever.
- Feathers do not differentiate into flight feathers.
- Thought to have lost power of flight at least 3-4 million years ago.
- Forages on the ground for invertebrates, seeds and vegetation.
- Population estimated around 250-400 birds.
This remarkable island-dwelling bird demonstrates that under the right environmental conditions, wings are dispensable for birds. With no need to fly or even glide in its predator-free habitat, the Inaccessible Rail has foregone wings entirely through evolutionary adaptation.
Upland Moa
The upland moa (Megalapteryx didinus) was a large, wingless bird endemic to New Zealand’s South Island. It became extinct around 1500 AD due to hunting by humans:
- A member of the moa family of flightless ratite birds.
- Reached up to 140 cm (4.6 ft) in height and weighed over 50 kg.
- Had no visible wings or wing bones.
- Adapted for a browsing lifestyle of eating leaves, twigs and small branches.
- Had a smaller and more upright posture compared to other moas.
- Population decimated after the arrival of Maoris who hunted them for food.
The upland moa’s complete lack of wings demonstrates that wings were unnecessary even for very large birds in the absence of predators and competition from mammals.
Elephant Birds
Elephant birds were a diverse group of enormous flightless birds that inhabited Madagascar until going extinct within the past 1000 years. Most species were wingless:
- Belonged to the family Aepyornithidae.
- Included the world’s largest birds – weighing up to 400-500 kg and 3 meters tall.
- Had small non-functional wings or were completely wingless.
- Were the dominant herbivores in Madagascar’s ecosystems.
- Hunted to extinction by humans and loss of habitat.
The elephant birds exemplify an interesting case where flight was abandoned and wings disappeared in gigantic birds that had dominated their ecosystems without predators for eons.
Conclusion
While most flightless birds retain non-functional wings or wing vestiges, a small number of species are truly wingless, lacking any wing remnants. These include the Inaccessible Island Rail (extant) and the extinct upland moa and elephant birds. Loss of wings occurred due to lack of predators and flying needs in their isolated habitats. Their examples show that under specific environmental situations, wings are not necessary for birds to thrive and can be eliminated entirely by evolutionary forces.