Alula

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alula

[′al·yə·lə]
(zoology)
Digit of a bird wing homologous to the thumb.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Alula

 

(also known as bastard wing or spurious wing), a group of feathers attached to the first digit of bird wings. The alula usually consists of four feathers, but sometimes there are three (certain passerines and Picidae) or six (the touraco). It can move forward and upward, preventing disruption of the airstream from the wing at large angles of incidence. The alula is most developed in forest birds that have rounded wings and are capable of maneuverable flight.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.