Anatomy: How do birds fold their legs in flight?

Today's anatomy lesson was inspired by Michelline who asked why she sees only peregrines' neatly folded talons when they fly.  Where do the rest of their legs go?

The bones in birds' legs are of nearly equal length and the hinges are opposite like an accordion.  This has two advantages: They can lower themselves straight down to sit on their eggs without tipping over and they can retract their legs to a nearly flat position in flight. 

To illustrate this I've highlighted the legs in red and numbered the joints: 

  1. From the body to joint #1 is the thigh (femur)
  2. Joint #1 to #2 is the shin (tibiotarsus) and calf (fibula)
  3. Joint #2 to #3 is the foot (tarsometatarsus)
  4. Joint #3 to the end are the toes.

On peregrines it's rare to see all those segments.  Their legs are much longer than we think!

The blue arrows show how birds fold their legs when they fly.  In step (a) the thigh and shin fold up flat to the body and are hidden in the body feathers.  In step (b) the foot and toes can do several things:

When you see only a peregrine's yellow toes in flight it's because his feet (which we call "legs") are extended backward and covered by his body feathers. 

Aeronautical engineers learned from birds.  Watch a jet take off and you'll see it retract its "legs" under its wings.

(bird skeleton by W. Ramsay Smith and J S Newell, 1889, via Wikimedia Commons, altered to illustrate the leg. Click on the image to see the original.)

5 thoughts on “Anatomy: How do birds fold their legs in flight?

  1. I would like to be able to do that; tuck my legs under & soar for awhile; have to walk today as always ; at least sun is out, but the cold reminds me that we will be having less & less warm days but it is always a treat to see who is singing & trying to find seeds to eat. Thanks for much for the blog and I feel so lethargic today; too much good good food yesterday!!!

  2. Thank you Kate! I appreciated the added links and especially the Saladin slideshow. These birds (all birds) are engineering marvels!

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