# Alula

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{{Short description|Small projections on the wings of birds}}
{{About|the anatomy of a bird's wing}}

thumb|280px|alt=Drawing of the various parts of a bird's wing|Location of the alula on a bird's wing
The '''alula''' {{IPAc-en|'|æ|l|j|U|l|@}}, or '''bastard wing''', (plural ''alulae'') is a small projection on the [anterior](/source/anterior) edge of the [wing](/source/wing) of modern [bird](/source/bird)s and a few [non-avian dinosaur](/source/non-avian_dinosaur)s.  The word is [Latin](/source/Latin) and means "winglet"; it is the [diminutive](/source/diminutive) of ''ala'', meaning "wing". The alula is the freely moving first digit, a bird's "thumb", and typically bears three to five small [flight feather](/source/flight_feather)s, with the exact number depending on the [species](/source/species). There also are minor [covert feather](/source/covert_feather)s overlying the flight feathers. Like the larger [flight feather](/source/flight_feather)s found on the wing's trailing edge, these alula feathers are asymmetrical, with the shaft running closer to anterior edge.

==Function==
[[File:Haliaeetus leucocephalus2.jpg|thumb|200px|alt=A large bird landing on its nest|Adult [bald eagle](/source/bald_eagle) landing, showing the alula in action]]
In most situations, the alula is held flush against the wing; however, it can be manipulated. When flying at slow speeds or landing, the bird moves its alula slightly upwards and forward, which creates a small slot on the wing's leading edge. This functions in the same way as the [slats](/source/Leading_edge_slats) on the leading edge of the wing of an aircraft, allowing the wing to achieve a higher than normal [angle of attack](/source/angle_of_attack) – and thus [lift](/source/lift_(force)) – without resulting in a [stall](/source/stall_(flight)).<ref>{{Harvnb|Ehrlich|Dobkin|Wheye|Pimms|1994|p=219}}</ref>  The tip of the alula forms a tiny vortex, acting similar to a [vortex generator](/source/vortex_generator), that forces the airflow over the wing to better bind to it.<ref>{{cite web|url=http://www.sciencedaily.com/releases/2015/06/150605103008.htm |title=Small vortex on the wing makes the elegance of birds' flight |author=Laboratory of Behavioral Ecology and Evolution at Seoul National University |date=5 June 2015 |access-date=5 June 2015}}</ref> During stretching of the wing down toward the ground, the alula is abducted from the wing and can be clearly viewed.

In falcons, the alula is more prominent, and provides a degree of control when the wing is cupped or tucked in a dive/stoop. The alulae are particularly notable in [peregrine falcon](/source/peregrine_falcon)s.{{Citation needed|reason=Unsourced statement that goes against previously sourced statements.|date=April 2021}}

==In ancient birds==
The presence of an alula has been confirmed in several now-[extinct](/source/extinct) ancient relatives of [modern bird](/source/Neornithes)s, including ''[Eoalulavis hoyasi](/source/Eoalulavis_hoyasi)'' (an [enantiornithine](/source/Enantiornithes) from the mid-[Cretaceous](/source/Cretaceous), 115<ref>{{Harvnb|Sanz|Chiappe|Pérez-Moreno|Buscalioni|1996}}</ref> [mya](/source/mya_(unit))) and the earlier ''[Protopteryx fengningensis](/source/Protopteryx_fengningensis)''.<ref>{{Harvnb|Zhang|Zhou|2000}}</ref> Since these [species](/source/species) are not closely related to modern birds, either the alula [evolved](/source/evolved) twice, or it did so more than 130 million years ago.

==See also==
*[Alular digit homology](/source/Origin_of_birds)
*[Bird flight](/source/Bird_flight)
*[Leading edge slot](/source/Leading_edge_slot), the man-made equivalent on fixed-wing aircraft

==Citations==
{{Reflist}}

==References==
{{Commons category}}

* {{citation |last1=Ehrlich |first1=Paul R. |last2=Dobkin |first2=David S. |last3=Wheye |first3=Darryl |last4=Pimms |first4=Stuart L. |title=The Birdwatcher's Handbook |year=1994 |publisher=Oxford University Press |isbn=0-19-858407-5 |url-access=registration |url=https://archive.org/details/birdwatchershand00ehrl }}
* {{citation|first1=J. L.|last1=Sanz| first2=L. M. | last2=Chiappe| first3=B. P. | last3=Pérez-Moreno| first4=A. D. | last4=Buscalioni| first5=J. J. | last5=Moratalla| first6=F. | last6=Ortega| first7=F. J. | last7=Poyato-Ariza |journal=[Nature](/source/Nature_(journal))|title=An Early Cretaceous bird from Spain and its implications for the evolution of avian flight|date=1996-08-01|volume=382|issue=6590|  pages=442–445|doi=10.1038/382442a0|bibcode=1996Natur.382..442S|s2cid=4284528}}
* {{citation |last1=Zhang |first1=Fucheng |last2= Zhou |first2= Zhonghe |title=A Primitive Enantiornithine Bird and the Origin of Feathers |pages=1955–1959 |journal=Science |date=8 December 2000 |volume=290 |issue=5498 |doi=10.1126/science.290.5498.1955 |pmid=11110660|bibcode=2000Sci...290.1955Z }}

{{Feather-tracts}}
{{Birds}}

Category:Feathers
Category:Bird anatomy

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Adapted from the Wikipedia article [Alula](https://en.wikipedia.org/wiki/Alula) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Alula?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.