How Birds Sleep on a Limb and a Northern Stray

By Dave Hanks
11/18/10

Perhaps, you have wondered how birds can sleep on a limb without falling off. Itís a matter of simple angle reduction. Tendons run from the birdís body, across its knees, over its heel joints, and connect to its toes. The joint that is visible in the photo is the heel. The knee joint is hidden by feathers and bends in the same direction as our knees bend. When the legs are straight these tendons have no tension placed upon them and are relaxed. The toes are unaffected at this time. When coming in to perch, the bird squats and by doing so the angle of the heel joints lessen. The tension created on the tendon by this angle reduction pulls on the toes, and they will now grip. As long as the bird remains squatted on a branch, the claws will stay locked and hold the bird firmly in place. This same result occurs in flight, when the bird draws its legs up under its body.

The White-Winged Crossbill pictured, shows this action. I was very surprised to see this species at the water in North Heglar Canyon. This species is an inhabitant of northern Canada and was definitely out of its range. This beautiful crossbill is adapted to opening cones and feeding on the seeds of conifers in the Boreal forest. The only other time Iíve had the luck to witness this species was in northern British Columbia.

It was with great excitement that I had this time with this special bird! It was one of the highlights of the photography year!

(This White-Winged Crossbill shows the squat position that locks his claws)


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