EPOW - Ecology Picture of the Week

Alula of the Anhinga

Australian Darter (Anhinga novaehollandiae), Family Anhingidae
Queensland, Australia

Explanation:  Proudly displaying its remiges (flight feathers) -- or more accurately, just trying to dry them out -- is this Australian Darter of genus Anhinga.  

There are four species of Anhinga, found in America, India, Africa, and here in Australia. This species is found throughout much of Australia, Papua New Guinea, and southern Indonesia, and occurs as an occasional vagrant in neighboring New Zealand.

But take a close look at the photo above; how many wings does this bird have?

The tiny winglets atop the main wings are actually attached to the bird's "thumb."  These feathers are called the bird's alula.  In this species, with wings outstretched, they appear somewhat separate from the main remiges (wing flight feathers).  But what the heck good are these tiny winglets?

Alulas actually aid in slow flight stability, increasing lift at slow flight speed (Lee et al. 2015).  It is a "high lift device located at the leading edge of the bird's wing" that functions like the leading edge of the wings of aircraft (Álverez et al. 2001).  

Alula feathers often are inconspicuous in many bird species, but in the darter it is prominent.  

Now you know!

Information:
     Álverez, J.C., J. Meseguer, E. Meseguer, and A. Perez.  2001.  On the role of the alula in the steady flight of birds.  Ardeola 48(2):161-173.
     Lee, S-i, J. Kim, H. Park, P.G. Jablonski, and H. Choi.  2015.  The function of the alula in avian flight.  Scientific Reports 5(Article 9914): doi:10.1038/srep09914.