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Birds are often associated with flight , but not all of them take to the skies . Around60 species — fewer than 1 % of all wench species — are flightless , including ostriches , penguin and kiwis . These birds evolve from flying ancestors but lose their ability to take flight , instead adjust to lifespan on land or in the water .
But why did they give up flight of stairs ? Why do n’t all bird fly ?
Penguins can’t fly through the air, but they retained their flight muscles and repurposed them for swimming.
The ability to aviate is especiallyuseful for escaping predatorsand traveling foresighted distances in hunt of nutrient and friendly animation conditions . However , flight require a lot of energy ; birds burn about75 % more energyper Clarence Shepard Day Jr. than likewise sized mammals do .
" If flight is n’t necessary , birds can better survive and reproduce if they divert that energetic investment elsewhere,“Natalie Wright , an associate professor of biota at Kenyon College in Ohio , say Live Science in an e-mail .
In a 2016 paper published in the journalPNAS , Wright and her colleagues mention that island - harp razzing , facing few to no marauder and less competition for food and habitat , incline to evolve toward flightlessness .
Penguins can’t fly through the air, but they retained their flight muscles and repurposed them for swimming.
" When living on an island without predators and without the need to migrate or journey long distance , for many kind of birds the costs of flight outweigh the benefits , " Wright said .
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The shimmy to flightlessness leads to physical modification in birds . Over evolutionary time , their pectoral escape muscles cringe . The sternum ( breastbone ) with its primal ridge ( keel ) — where flight muscles attach — also becomes smaller , Wright say . fender clappers — the humerus , ulna and carpometacarpus — become short and less racy , while their leg raise longer and sturdier as an adaptation to a more terrestrial life style , she added .
Kiwis are flightless birds whose feathers have lost their barbules, the tiny, hook-like structures that usually keep birds aerodynamic. This gives kiwis a fluffier, fur-like appearance.
Some birds have traded flight for superscript swim abilities . Penguins , for instance , retained their flying muscles and keel but repurposed them for swimming . " They use their extension to fly underwater,“Peter Ryan , a professor emeritus of ornithology at the University of Cape Town in South Africa , evidence Live Science in an email . Theflightless auk(Pinguinus impennis ) also employ its wings to move itself through water .
In birds that have been flightless for a recollective fourth dimension , the tenacious , soaked feathers demand for flight ( flight feather ) disappear too , Ryan suppose . In some specie , like kiwis and the Inaccessible Island track ( Atlantisia rogersi ) , the body feathering lose barbules — the tiny , hook shot - like structure that normally keep them flowing — give them a fluffier , pelt - like appearing , Ryan added .
A 2025 study publish in the journalEvolutionfound that flightless birds lose feather features in the reverse order of how they first acquire . The inquiry also conclude that gaunt change go on before changes in plumage , as it takes significantly more energy to turn and maintain bones than it does to sustain feathers .
Although flightless fowl are rare today , fossils reveal that they were far more dominant and diverse a few thousand year ago , Tim Blackburn , a professor of invasion biota at University College London , told Live Science in an email . However , the arrival of humans and animals like crumb and dogs uncover these hoot to marauder .
" Having sacrificed their electrical capacity to take to the atmosphere , there was no metre for them to re - evolve this useful ability , " Blackburn articulate . This led to the rapid extinction of iconic birds like thedodo(Raphus cucullatus ) on Mauritius , the moa in New Zealand , and many others .
A 2020 study co - authored by Blackburn and published in the journalScience Advancesfound that there would be four meter as many flightless razz specie on Earth today were it not for human being - driven extinctions .
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The exit of flight happened at least 150 times in dissimilar groups of birds throughout evolutionary history , Ferran Sayol , first author of the study and a researcher at Centre for Ecological Research and Forestry Applications ( CREAF ) in Barcelona , Spain , told Live Science in an email .
" Many of these species thrived on islands without predators but vanish short after when humans arrived ( due to unmediated hunting or introduced vulture ) , making flightlessness seem rarer than it actually was , " Sayol say .
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