Why are Some Birds Flightless?

Flightless birds have adapted this trait due to their size and specific environmental needs.

Aug 11, 2023bySara Payne
why are some birds flightless

Birds are usually synonymous with flight, but there are several flightless bird species in the world. Ostriches, emus, kiwis, penguins, and cassowaries can’t fly because their bodies have adapted differently to the environments they live in.

Even though these birds are grounded, they’ve adapted other skills to make up for their flightlessness.

Grounded Birds: Flightless for a Reason

There are over 50 species of flightless birds in the world

Flight is a great adaptation for birds because it helps them to migrate, find food, and get away from predators. Yet, flight also expends a lot of energy for a bird. According to the University of Louisiana, birds who fly need a large pectoralis muscle. This muscle takes time to grow, and it uses much of the birds’ energy to maintain. Flight is an adaptation to better compete with other animals for resources.

Yet, if there is no need to compete in this way, it is beneficial for birds to adapt to lose flight to conserve energy.

Some bird species adapt more easily to flightlessness than others. One large factor tends to be isolation on an island. Isolated birds didn’t need to fly because they have little competition in their terrestrial habitat.

Another factor for flightlessness is a bird’s body structure. Many of the largest, flightless birds belong to the Ratite family. This family of birds is missing the keel, a ridge on the breastbone. The keel is where the muscles essential for flying are attached. Without this structure, Ratites cannot fly.

However, some birds adapted a different use for their wings. This is the case for penguins who swim instead of taking flight.

Although scientists originally believed flightless birds all originated from a common ancestor, they are finding that flightlessness is actually an adaptation occurring naturally in different bird species throughout the world.



Ostriches are found in sub-Saharan Africa, where they dwell in mostly savanna and scrub forest biomes. In these arid climates, being on the ground is beneficial to them where they can feed on vegetation and insects.

They are also the largest birds on Earth. They can get to 9 feet tall and weigh up to 320 pounds. This adaptation means they have few predators, except big cats. They developed strong running legs to escape the lions and cheetahs that prey on them.

Their wings, instead of flight, are used for balance as they run. Their wingspan is also used to aid in courtship, where they perform an elaborate mating dance.



Living in Australia, emus are the second largest bird in the world. They can get up to 5 feet tall and weigh around 100 pounds.

Flightless birds, such as the emu, have bigger bodies and longer legs. These legs give them the advantage of speed. In emus, they can also use their legs and a large toe claw to kick at predators who may be cornering the bird.


kiwi bird

Remarkably, New Zealand is home to more species of flightless birds than anywhere else on the planet. Before humans arrived, there were no land mammals that preyed on these birds, so they didn’t need to fly to escape from predators.

Birds, such as the flightless kiwi, could forage safely on the forest floor. Kiwis are an unusual bird species. They have a vestigial wing with a claw on the end that they hide beneath their fur-like feathers. Their shortened wings make it impossible for them to fly.


penguin swimming

Unlike the other flightless birds on this list, the penguin is not a part of the ratite family. Penguins dwell mostly in the Southern Hemisphere of the world. They vary in size, shape, and coloration, but they have some traits in common.

Penguins have a common ancestor with petrels and albatrosses, but instead of flying, they became adept swimmers. This is likely due to a lack of food resources on land and an abundance of fish in the waters.

These beautiful birds have adapted larger stomachs to hold more food. They also have dense bones, which makes diving and swimming easier. To out-compete other birds, their density lets them dive deeper, getting more fish.



The cassowary is another flightless bird of the ratite family that lives in Australia. This bird is related most closely to the emu, and because of its lack of keel in the chest bone, they have adapted ways to survive on the ground.

Without flight, the cassowary learned how to fight. These birds can jump about 6 feet off the ground. They also have a bony helmet, called a casque, that is made of keratin on their heads and dagger-like nails on their feet. These 5-inch nails have been known to kill humans, so these birds can be rather dangerous.

Sara Payne
bySara Payne

Sara is a mother of two and a high school English teacher who rediscovered her love of writing during the pandemic. She has 5 rescue cats: Neville and Luna, who are white cats with black and grey spots, and Ginny, Blue, and Fairy, who are calicos. Besides taking care of humans and fur babies, Sara enjoys gardening, crafting, and spending time in nature.