Have you ever wondered how some birds manage to sleep perched in trees? Wouldn’t you think that they would fall off their branches once their bodies relaxed into sleep?
Well, the answer is in the feet. Half of all the types of birds in the world are in a category called passerine. One of the defining features of passerine birds is the way the feet are shaped and function. Passerine (perching) birds have four toes on each foot. Three of the toes face forward. One toe faces backward. When a bird lands on a tree branch, its toes wrap around the branch and then lock into place. This automatic locking of the toes is a very good thing: passerine birds can relax and sleep without worrying their feet will stop gripping their perch.
You can tell a lot about a bird by what kind of feet it has. As another example, if you see a bird with webbed feet, you can bet it is a swimmer. Webbed feet are terrific for swimming because the large surface area of the foot is perfect for pushing water around.