When we moved to Shepherdstown, St. Agnes was in the process of building a new church building. Shortly after the building was occupied, I was asked to build some Bluebird houses to be installed at various locations on the grounds. I didn’t know how to build a bird house with all the characteristics necessary to attract a specific type of bird — in this case, the particular type of Bluebird native to this area. I of course googled plans of how to build such a birdhouse.
I was cleaning out some old computer files the other day and ran across those plans and another interesting article about birds that I had saved for some reason. The article was about how birds sleep on tree limbs without falling off….
Nest building birds don’t sleep in nests — they just use them to raise their families. Some birds crouch down in the grass or in bushes to get their sleep. But there are many species of birds that sleep while perched on tree limbs. It seems pretty amazing that they could stay up in a tree while asleep because when people (and lots of animals) fall asleep, they usually go limp. But most of the birds in this area belong to an order known as passerines — birds with feet that are adapted for perching.
Most birds have four toes on each foot, and these toes can be arranged in different configurations — depending on the type of bird. A passerine typically has three toes that face forward and a “big toe,” or hallux, that faces backward.These birds have an ingenious tendon-locking mechanism (TLM) that causes a special ligament in the back of the leg to tighten automatically when the bird sits on a limb.
The tendon locks the toes and secures the bird to the perch. Because of the TLM, the bird doesn’t have to keep its muscles actively engaged to maintain its grip — the bird stays on the limb until it retracts its toes. Other animals, like bats, have a similar mechanism that allows them to hang upside down without falling.
It’s interesting, and maybe a little morbid, that the TLM doesn’t disengage when a bird dies. Skeletons have been found still perched in trees — In fact I found one many years ago when I cut down a small tree…..
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