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.
You may have heard of the
Achilles’s tendon, 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 were injured, the foot
would be almost immobilized. This is how, in mythology, Achilles was killed –
Paris shot an arrow into Achille’s tendon.
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 (tarsometatarsus)! 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 runs from above the ankle 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 initially relax and the bird just falls out of the tree.
In another blog I’ll tell you why you don’t see as many dead birds as you do
mammals, either in the woods or as roadkills.
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