Anatomy: How do birds fold their legs in flight?

Diagram of bird skeleton showing how legs fold for flight (image from Wikimedia Commons)

26 November 2010

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 means birds can fold their legs to lower their bodies straight down to sit on eggs and they can retract their legs to a 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 toes.

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For most birds, even when standing, the thigh is hidden in the body feathers. Birds’ legs are much longer than we think! See how long a juvenile peregrine’s legs are in this slideshow.

The blue arrows above 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 toes may do one of several things.

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When you see only a peregrine’s yellow toes in flight it’s because his legs and feet are 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 caption to see the original.)

6 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!

  3. Thanks for this… I’m an abstract-leaning artist and I wanted to make my faux-birdish shapes appear to by flying. Big help!

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