Why Don’t Sleeping Birds Fall Out of Trees?

WHY DON”T SLEEPING BIRDS FALL OUT OF TREES?

Birds have a skeletal system with a number of adaptations for their way of life. Flying especially requires a number of adaptations to make the birds’ bones lighter and stronger. Many bones are fused into one, some are hollow, and most have internal struts for strength. Flying birds have a keel extending from their sternum to which the flight muscles are attached. If you debone chicken breasts, that’s the big bone you remove in the process. Flying birds, swimming birds, and flightless birds all have special skeletal adaptations.

Ever wonder why a sleeping bird doesn’t just pitch forward and fall off the branch it is perched on in the middle of a nap? How about the birds perched in trees and shrubs or on power lines on a windy day? Are they just hanging on for dear life, hoping they don’t get blown off? The answer is that songbirds are well adapted to their perching life. In fact, in ornithological parlance, the terms “songbirds” and “perching birds” are interchangeable.

The Achilles’s tendon is the tendon that extends from our calf muscle around the back of our foot to the heel. Reach down right now on your leg and feel it. This tendon enables us to flex our foot up and down – try it. If the Achilles tendon becomes injured, the foot would be almost immobilized. This is how, in mythology, Achilles was killed – Paris shot a poison arrow into Achille’s heel where the tendon attaches.

Look at this diagram of a bird’s leg. There are the toes, of course, but notice that the long bone above the foot is actually the ankle!  The tibia and fibula, which make up our lower leg bone, are hidden by the bird’s feathers, as is the femur. So while humans have two long bones leading from the hip to the foot, birds have three.

In birds, the Achille’s tendon extends from the gastrocnemius muscle runs just above the the ankle – the ankle in the diagram is indicated by the tibialis anticus lines- to the back of the foot and then along the bottom of the toes. When a bird lands on a branch, the ankle bends and the Achilles’ tendon is stretched. When the tendon stretches, it pulls on the toes and curls them around the branch. There is no muscular effort involved in holding onto the branch – it’s automatic. When the bird takes off, the legs straighten, the tendon relaxes, and the toes release their hold on the branch.

Well, now you might wonder why you don’t occasionally see a dead bird sitting on a branch, having died in its sleep from exposure to cold or just old age.
In death, the muscles relax and the bird just falls out of the tree. In another blog you can discover why you don’t see many dead birds laying around..

One thought on “Why Don’t Sleeping Birds Fall Out of Trees?

  1. Roger,

    Yet another fascinating post. I did know that a bird’s feet “lock” onto branches, wires etc but I did not know the biomechanics involved. So thanks for the explanation. A question though : why are some birds better at “locking” on than others? I ask this as I have noticed some of our local birds appear to “botch” their landings on branches, wires etc. Thanks, Peter

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