Editing Flightless bird (section)

===Continued presence of wings in flightless birds===
Although [[selection pressure]] for flight was largely absent, the wing structure has not been lost except in the New Zealand moas.<ref name="Baker, A. J. 2014"/> Ostriches are the fastest running birds in the world and emus have been documented running 50&nbsp;km/h.<ref name="Noble, J. C. 1991"/> At these high speeds, wings are necessary for balance and serving as a parachute apparatus to help the bird slow down. Wings are hypothesized to have played a role in [[sexual selection]] in early ancestral ratites and were thus maintained. This can be seen today in both the rheas and ostriches. These ratites utilize their wings extensively for courtship and displays to other males.<ref name="Cracraft, J. 1974"/> Sexual selection also influences the maintenance of large body size, which discourages flight. The large size of ratites leads to greater access to mates and higher [[reproductive success]]. Ratites and tinamous are monogamous and mate only a limited number of times per year.<ref>{{Cite journal | doi=10.1111/j.1095-8312.1985.tb00387.x|title = The mating systems of ratites and tinamous: An evolutionary perspective| journal=Biological Journal of the Linnean Society| volume=25| pages=77–104|year = 1985|last1 = Handford|first1 = Paul| last2=Mares| first2=Michael A.}}</ref> High parental involvement denotes the necessity for choosing a reliable mate. In a climatically stable habitat providing year-round food supply, a male's claimed territory signals to females the abundance of resources readily available to her and her offspring.<ref name="Cubo, J 2000"/> Male size also indicates his protective abilities. Similar to the emperor penguin, male ratites incubate and protect their offspring anywhere between 85 and 92 days while females feed. They can go up to a week without eating and survive only off fat stores. The emu has been documented fasting for as long as 56 days.<ref name="Noble, J. C. 1991"/> If no continued pressures warrant the energy expenditure to maintain the structures of flight, selection will tend towards these other traits.

In [[penguin]]s, wing structure is maintained for use in locomotion underwater.<ref>{{cite book |doi=10.1002/9781119990475.ch6 |chapter=Penguins Past, Present, and Future: Trends in the Evolution of the Sphenisciformes |title=Living Dinosaurs |date=2011 |last1=Ksepka |first1=Daniel T. |last2=Ando |first2=Tatsuro |pages=155–186 |isbn=978-0-470-65666-2 }}</ref> Penguins evolved their wing structure to become more efficient underwater at the cost of their efficiency in the air.<ref>{{cite journal |last1=Elliott |first1=Kyle H. |last2=Ricklefs |first2=Robert E. |last3=Gaston |first3=Anthony J. |last4=Hatch |first4=Scott A. |last5=Speakman |first5=John R. |last6=Davoren |first6=Gail K. |title=High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins |journal=Proceedings of the National Academy of Sciences |date=4 June 2013 |volume=110 |issue=23 |pages=9380–9384 |doi=10.1073/pnas.1304838110 |doi-access=free |pmc=3677478 |pmid=23690614 |bibcode=2013PNAS..110.9380E }}</ref>

The only known species of flightless bird in which wings completely disappeared was the gigantic, herbivorous [[moa]] of [[New Zealand]], hunted to extinction by humans by the 15th century. In moa, the entire [[Shoulder girdle|pectoral girdle]] is reduced to a paired [[scapulocoracoid]], which is the size of a finger.<ref>{{cite journal |last1=Huynen |first1=Leon |last2=Suzuki |first2=Takayuki |last3=Ogura |first3=Toshihiko |last4=Watanabe |first4=Yusuke |last5=Millar |first5=Craig D |last6=Hofreiter |first6=Michael |last7=Smith |first7=Craig |last8=Mirmoeini |first8=Sara |last9=Lambert |first9=David M |title=Reconstruction and in vivo analysis of the extinct tbx5 gene from ancient wingless moa (Aves: Dinornithiformes) |journal=BMC Evolutionary Biology |date=December 2014 |volume=14 |issue=1 |page=75 |doi=10.1186/1471-2148-14-75 |doi-access=free |pmid=24885927 |pmc=4101845 |bibcode=2014BMCEE..14...75H }}</ref>