The Snowy Owl was elusive today as I drove through the fog shrouded Horicon Marsh. Several vigilant hawks were perched high in trees, including this Red-tailed Hawk.
He fans his reddish brown tail feathers as he takes flight, confirming his identity.
Sharing the backside of a hawk flying away isn’t a prize winning shot. What I found interesting though, is how relaxed his feet are as he releases his grip on the tree branch.
Hawks have three main leg bones that form a “Z.” Muscles that attach to the back of the leg bones have long tendons. These tendons pass through grooves behind the “ankle” and end at the underside of the toes. (Tendons attach muscles to bones.) Think of the tendon as a big rubber band going over a pulley. When a hawk straightens its leg, the muscle contracts and shortens. There is less tension on the tendon since it does not have to travel as far, and the toes open. A hawk uses this mechanism when it approaches a perch or its prey. The hawk then flexes its legs to grasp the perch or prey. Flexion stretches the tendon and puts more tension on it, causing the toes to close. We have a similar mechanism in our wrists and hands. Try to bend your wrist back and grasp a pen. Then bend your wrist down as far as you can. Your grasp will loosen on the pen and it will be harder to hold. This is referred to as a tenodesis grip in humans and is used as a tool in physical and occupational therapy to rehabilitate damaged tendons.
A hawk’s body weight increases the effect. This passive closing of the toes allows the muscles to relax and the hawk can stay perched for long periods of time without expending energy.
Hawks also have keen vision. As soon as they see my car slowing down, off they go to find another lookout post to survey the Horicon Marsh.