Red-tailed hawks, our most common hawk, are slightly smaller than goshawks, the latter weighing 3 pounds or less. Red-tails are said to have a foot grip of 200 pounds per square inch (psi).

The goshawk grip, the one you don't want to test, would be slightly stronger. (This is a number hard to find; these are research estimates.)

For comparison, how strong is your grip?

Find a bathroom scale, the one with its numbers down there between your feet.

Hold the scale with both hands, face toward you. Squeeze hard! The number you reach is your squeeze score.

Now, open your hand and estimate the number of square inches in your palm. My hand is small, palm 3-by-4 linear inches, 12 square inches.

My squeeze score — how hard I press the scale — is 30. I divide 12 into 30 to get my pounds per square inch. A paltry 2.5 psi. A raptor I am not.

Goshawks have a killer grip at 200-plus psi. Bald and golden eagles? Grip pressure is estimated as high as 400 psi. Great horned owls, around 300 psi.

High-speed photography has shown a goshawk's strike speed to be near 50 miles per hour. In this test, talons closed about 25 milliseconds after impact with prey. In less than a second the bird was working to drive talons deeper.

Most raptors don't hit a home run every time they strike at prey. Success is said to be about one for 10. But when they get a hit, escape from that grip is just luck.

The relaxed state of your hand is fingers-open. You make an effort to grip, contracting finger muscles. Birds' toes are the opposite, gripping all the time. Birds make an effort to open.

That's why birds can sit on branches and wires with such ease, even while sleeping. They open their toes to land, and the grip automatically clicks into action when they touch the perch.

The grip of a raptor is triggered when its foot pads touch prey. Like a trap sprung, the talons snap tight and dig in. Release is a decision the bird makes.

There are four toes on the raptors' foot, three to the front, one to the back. The latter is longer. Hawks and owls can drive pin-sharp talons deep. That rear toe is long enough to puncture animal organs.

In her marvelous book "H Is for Hawk" author Helen Macdonald writes of "taming" a goshawk, taking it into the field to hunt rabbits and pheasants. (Taming doesn't mean everything implied.)

"One afternoon Mabel [the hawk] leapt up from her perch to my fist," Macdonald wrote. "She lashed out with one foot and buried four talons in my bare arm. Blood was dripping on the kitchen floor. I could do nothing. Her grip was too powerful.

"I had to wait until she decided to let go," Macdonald wrote.

No reason for the attack was given, but these birds, wickedly strong, are never not wild.

In a study published by National Geographic in 2009, the author said that his next research would compare raptor feet with those of certain carnivorous dinosaurs. Those dinosaurs also had large talons.

And some dinosaurs evolved to become birds. You probably wouldn't have wanted to shake hands with them, either.

Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at startribune.com/wingnut.

Bald eagles’ talons — and those of other birds — default to a gripping position. (The Minnesota Star Tribune)