why are there flightless birds

How many flightless birds are there?

The world is home to about 40 different species of flightless birds, such as ostriches, emus, cassowaries, rheas, kiwis, and penguins. Compared to flying birds, a flightless bird has smaller wings, a smaller breastbone (which stabilizes the flight muscles), and more feathers.

History edit

Immediately following the K-Pg extinction event, which destroyed all non-avian dinosaurs and large vertebrates 66 million years ago, there were divergences and losses of flight within the ratite lineage. [6] Following the mass extinction, niches were quickly cleared out, giving Palaeognathes the chance to disperse and settle in new areas. By changing their morphology and behavior, new ecological influences selectively forced various taxa to converge on flightless modes of existence. The effective annexation and defense of a territory claimed by ratites, whose Tertiary ancestors were chosen for their large size and cursoriality [7] Throughout the Miocene, temperate rainforests dried out and turned into semiarid deserts, resulting in a wide dispersion of habitats over the increasingly diverse landmasses. Cursoriality was an economical way to cover large distances in order to obtain food, which was typically found in low-lying vegetation that was easier to walk to. [7] The distribution of ratite in semiarid grasslands and deserts today reflects remnants of these events. [8].

Bird gigantism and flightlessness are almost exclusively associated with islands that lack competition and mammalian or reptilian predators. Ratites, on the other hand, live in areas that are primarily inhabited by a variety of mammals. [10] It is believed that the breakup of the supercontinent Gondwana led to allopatric speciation, which is where they first originated. [11] Nevertheless, subsequent data indicates that Joel Cracraft’s 1974 theory is false. [12] Rather ratites lost their ability to fly multiple times within the lineage after arriving in their respective locations via a flighted ancestor.

Gigantism is not a requirement for flightlessness. Despite coexisting with the gigantism-exhibiting moa and rheas, the kiwi and tinamous do not display gigantism. This may be due to the arrival of distinct ancestral flighted birds or to competitive exclusion. [11] The large flightless herbivore or omnivore niche was occupied by the first flightless bird to arrive in each environment, forcing the subsequent arrivals to stay smaller. It’s possible that after the K/T Boundary, there were no voids in the environments for flightless birds to occupy. They were pushed out by other herbivorous mammals. [10].

More species of flightless birds than any other place were found in New Zealand, including the kiwi, several species of penguins, takah?, weka, moa, and several other extinct species. One explanation for this is that, prior to the advent of humans some a millennium ago, New Zealand was devoid of large land mammals; instead, larger birds served as the primary predators of flightless birds. [13].

Ratites are thought to have independently evolved flightlessness several times within their own group. They are members of the superorder Palaeognathae, which also includes the volant tinamou. [4][6][7][10] On oceanic islands, for example, some birds developed a lack of ability to fly in response to the lack of predators. Ratite phylogeny and Gondwana’s geological past are inconsistent, suggesting that flying birds caused a secondary invasion that led to ratites’ current distribution. [14] There’s still a chance that the tinamou regained flight after their most recent common ancestor, the ratites, was flightless. [15] Nonetheless, it is thought that losing flight is a simpler transition for birds than losing flight and then gaining it again, as this has never been recorded in the history of birds. Furthermore, the fact that tinamou nest inside flightless ratites suggests that ancestral ratites were volant and that several independent losses of flight occurred throughout the lineage. This suggests that convergent evolution is the cause of the ratites’ unique inability to fly. [16].

Continued presence of wings in flightless birds edit

With the exception of New Zealand moas, the wing structure has not been lost despite the lack of selection pressure for flight. [11] Emu runs have been recorded at 50 km/h, and ostriches are the world’s fastest runner birds. [8] The bird needs its wings to maintain balance at these high speeds and to act as a parachute to slow down. It is believed that wings were preserved because they were important for sexual selection in early ancestral ratites. These days, ostriches and rheas both exhibit this. These ratites make extensive use of their wings during displays to other males and during courtship. [12] Sexual selection affects the preservation of large body size as well, which deters flight. Ratites’ large size facilitates easier mate selection and increases the likelihood of successful reproduction. Because they are monogamous, rats and tinamous only mate a few times a year. High parental involvement indicates that selecting a trustworthy partner is essential. In an environment with a stable climate that offers year-round food supplies, a male’s claimed territory alerts females to the wealth of resources that are easily accessible to them and their progeny. [20] Male size also indicates his protective abilities. Like emperor penguins, male ratites spend 85–92 days incubating and guarding their young while the females feed. They can only survive on fat reserves and go up to a week without eating. There are records of emus fasting for up to 56 days. [8] Selection will lean toward these other features if there are no ongoing stresses that justify expending energy to maintain the flight structures.

Penguins’ wings are kept in their original structure so they can move underwater. [27] Penguins lost some of their aerial efficiency as a result of evolving their wing structure to become more efficient underwater. [28].

Hunted to extinction by humans by the 15th century, the massive, herbivorous moa of New Zealand was the only known species of flightless bird in which wings entirely vanished. The entire pectoral girdle in moa is reduced to a pair of finger-sized scapulocoracoids. [29].

FAQ

Why do birds have wings if they can’t fly?

Even flightless birds, which are descended from flying ancestors, use their wings for balance, display, and other purposes. The origins of these extraordinary appendages date back to the time of dinosaurs, but the cause of their development remains a mystery.

Why are there birds that don’t fly?

Some birds don’t fly, like penguins, ostriches, emus, kiwis, and others. It is thought that these birds lost their ability to fly because there weren’t any predators on the islands in which they evolved.

Why did ostriches evolve to not fly?

As time passed, and evolution began to take its course, the ostrich began to gain in size and adapt to their “new” life. And as these birds got bigger, they began to lose the ability to fly. The common misconception of the ostrich is that its ancestor was also a flightless bird: THIS IS INCORRECT!

Can flightless birds fly once?

Flightless birds alive today evolved from flying birds, which evolved from flightless dinosaurs. Some dinosaurs of the raptor kind may have become secondarily flightless. As far as we can tell, all birds came from a single common ancestor, and that ancestor was capable of flight.