The alula , or bastard wing, (plural ''alulae'') is a small projection on the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

edge of the

wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...

of modern

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s and a few

non-avian dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is ...

s. The word is

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

and means "winglet"; it is the

diminutive A diminutive is a word obtained by modifying a root word to convey a slighter degree of its root meaning, either to convey the smallness of the object or quality named, or to convey a sense of intimacy or endearment, and sometimes to belittle s ...

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 Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tai ...

s, with the exact number depending on the

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. There also are minor covert feathers overlying the flight feathers. Like the larger

s found on the wing's trailing edge, these alula feathers are asymmetrical, with the shaft running closer to anterior edge.

Function

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 on the leading edge of the wing of an aircraft, allowing the wing to achieve a higher than normal

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...

– and thus lift – without resulting in a stall. The tip of the alula forms a tiny vortex, acting similar to a

vortex generator A vortex generator (VG) is an aerodynamic device, consisting of a small wikt:vane, vane usually attached to a lifting surface (or airfoil, such as an aircraft, aircraft wing) or a rotor blade of a wind turbine.peregrine falcon The peregrine falcon (''Falco peregrinus''), also known simply as the peregrine, is a Cosmopolitan distribution, cosmopolitan bird of prey (raptor) in the family (biology), family Falconidae renowned for its speed. A large, Corvus (genus), cro ...

In ancient birds

The presence of an alula has been confirmed in several now-

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

ancient relatives of modern birds, including ''

Eoalulavis hoyasi ''Eoalulavis'' (from the Ancient Greek: Eos, ''Éōs'', "dawn"; ''alula'', alula, "bastard wing"; ''avis'', "bird") is a monotypic taxon, monotypic genus of Enantiornithines, enantiornithean bird that lived during the Barremian, in the Lower Cret ...

'' (an enantiornithine from the mid-

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

, 115 mya) and the earlier '' Protopteryx fengningensis''. Since these

are not closely related to modern birds, either the alula

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

twice, or it did so more than 130 million years ago.

Citations

References

* * * {{Birds Feathers Bird anatomy

Function

In ancient birds

See also

Citations

References