American Kestrel during a dive extends his alulas. What purpose does this serve?
"The alula functions similar to a thumb. Located at the beginning of the primaries, the alula is flexible and independent and can be used to create faster air currents over the inside of the primaries. This small wing, which can be drawn forward, is used on the downstroke. It increases lift, reduces turbulence, and is used to control stall and braking when landing." The Illustrated Birds of Prey by Denny Rogers et al
I would add that it is used for control of flight during a dive or at high speed as I have many photos indicating the use of alulas at this time in the kestrel's flight.
Fabulous Bill. Thanks for sharing this. I had no idea that falcons used the alula or "******* wing", as it is sometimes called, like this. I think what is clear is happening in this case is that falcons like the kestrel are designed like a jet which has wings that can swing back and forth. In a steep, fast dive, the main wing is swept back leaving the alulas to provide stability and steering. Anyway, that's what I think this very illustrative image is saying. BTW, in most/all birds the alula consists of the outermost primary and coverts (smaller feathers overlaying the primary).
Modertor's note- political correctness imposed by BPN has produced the asterisks above. The perfectly well accepted alternative name for the alula is the
"b a s t a r d_w i n g". I don't think BPN is clever enough to edit this version out!
Last edited by John Chardine; 04-22-2009 at 03:31 PM.
Ed- I think what I said was "bass-ackwards"! Thanks for pointing it out- I know you were having fun! But seriously, I don't think aeronautical engineers know much about falcon flight (apologies to all of you out threre if I'm wrong), so it's more likely that falcons and jet aircraft "evolved" independently but came up with similar solutions to the problem of high speed, controlled flight. If so this an example of convergent evolution whereby two evolutionarily unrelated "species" look or work in a similar manner. I know jets did not evolve in a biological sense but the principle applies nevertheless. A good example from the bird world might be diving-petrels and auks which are unrelated but which both show physical features that are designed for diving under the water.
I don't know about alulas or much at all. :D But your image is incredible. How the he11 (can't edit that BPN PC) did you keep focus on it? I am totally blown away!
Akos,
Keeping a lock on this guy, as well as swallows and other fast little guys, can be done with practice, high shutter speed, fast camera (Canon MkIII) and a fast focusing lens. In this case I used my Canon 400 5.6f. Even when the lens is switched to short focus I can still acquire these guys.
Another part of the equation is to always be ready, shoot in Manual mode and try to get a shutter speed near 1/1600. I also use a bushhawk which steadies my camera and allows me to pan better, especially with this small lens.