are there birds without wings

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].

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].

Morphological changes and energy conservation edit

The smaller wing bones of flightless birds[17] and the absence or significantly reduced keel on their breastbone are two important characteristics that set them apart from flying birds. (The keel anchors muscles needed for wing movement. )[18].

Two inverse morphological changes in the skeleto-muscular system result from adapting to a cursorial lifestyle: paedorphically reduced pectoral apparatus for power flight and enlarged pelvic girdle for running due to peramorphosis. [11] Consistent selection for cursorial traits among rats indicates that these adaptations consist of an enhanced energy efficiency during adulthood. The term “ratite” originates from the Latin word ratis, which means raft—a boat without a keel. Their sternum is flat and lacks a keel, similar to a raft, which sets it apart from the sternum of most flying birds. This structure serves as the attachment site for the flight muscles, enabling powered flight. However, ratite anatomy exhibits additional primitive features intended for flight, including the merging of wing components, the presence of a cerebellar structure, a pygostyle for tail feathers, and an alula on the wing. [12] These morphological traits suggest some affinities to volant groups. Among the first to settle in new niches, palaeognathes were unrestricted in their growth until food and territory became scarce. A study on energy conservation and the evolution of flightlessness proposed that the loss of flight causes intraspecific competition to select for a lower individual energy expenditure. [19].

Given that some island bird species are closely related to those that can fly, it appears that flight comes at a significant biological cost. [19] The most expensive means of propulsion found in the natural world is flight. Because flying requires more energy than a smaller body, flightlessness frequently corresponds with larger body mass. [8] Ratites lower their basal metabolic rate and preserve energy by decreasing their large pectoral muscles, which demand a substantial amount of total metabolic energy. [19][20] A study examining bird basal rates discovered a strong link between kiwis’ low basal rate and their pectoral muscle mass. On the contrary, flightless penguins exhibit an intermediate basal rate. This is probably due to the fact that penguins’ pectoral muscles, which are used for swimming and hunting, are highly developed. [19] A cursorial lifestyle is more cost-effective and facilitates easier access to dietary requirements for ground-feeding birds. [7] The wing and feather structures of flying birds are different from those of flightless birds, which are better suited to their surroundings and activities, like diving into the ocean. [21].

Species with certain characteristics are more likely to evolve flightlessness. For instance, animals with shorter wings naturally have a higher chance of losing their ability to fly. Certain species will develop flatter wings in order to enhance their underwater mobility, even if it means sacrificing their ability to fly. Additionally, birds are more likely to develop flight loss if they experience simultaneous wing molt, which is the annual replacement of all of the feathers in their wings. [24].

There are several bird species that seem to be gradually losing their ability to fly. These consist of the Laysan duck of Hawaii, the Okinawa rail of Japan, and the Zapata rail of Cuba. These birds have all recently evolved from fully flighted ancestors and exhibit adaptations common to flightlessness, but they have not entirely given up the ability to fly. They cannot, however, fly well enough to cover great distances in the air. [25].

FAQ

Are there any wingless birds?

Which bird has no wing?

Do all birds have wings?

Can a bird fly without wings?