Eagles keep a tight grip on prey

The bald eagle weighs 12 pounds, the fish it just captured 3 pounds. The eagle flies to its nest, carrying 25% of its own weight.

That's like you carrying a 5-gallon bottle of water, which weighs 43 pounds, however far that eagle flies.

The task is twofold. You have to be able to lift the bottle, and then you have to maintain grip; don't drop it.

Raptors' gripping strength allows the birds to both kill and carry prey. The eagle can exert grip pressure upward of 400 pounds per square inch (psi), according to scientists at HawkQuest, an environmental education organization in Colorado.

Researchers believe that an eagle's gripping strength is about 10 times that of an adult human hand. Eagles are strong enough to drive needle-sharp talons deep into prey. A strike can cause severe damage to an animal's internal organs, causing death.

A great horned owl's talon grip is estimated at 500 psi. The owl has relatively short talons, so it might not kill on strike. One of its four toes swivels backward, giving the bird two pairs of opposable talons. The owl can squeeze (500 psi) to kill its prey.

Years ago while cross-country skiing I came upon a 10-foot circle of rabbit fur. I assumed an owl had dropped down and snatched the rabbit. It must have been a powerful hit. It looked like the bunny had exploded.

The power of a raptor's grip comes from its leg muscles, tendons and bones, according to the website hawkquest.org.

First, tendons attached to the leg contract. Leg muscles pull the talons tight.

"The tendons are contained in tendon sheaths. Both the tendons and sheaths have tiny ridges. When the tendon is contracted the ridges on the tendons and the tendon sheaths interlock, creating a kind of 'ratchet' effect," hawkquest says.

"This enables the bird to maintain tremendous pressure on the talons without continuously maintaining the tremendous contraction force on the muscle.

"As a result, a raptor is able to keep its talons closed over long periods of time while subduing relatively large prey," the site says.

Different raptor species have different gripping strengths depending on the type and strength of prey they pursue. In Minnesota the golden eagle would be considered by most experts to have the strongest grip. It eats small mammals, waterfowl and carrion.

The maximum weight most golden eagles can lift is 11 pounds, give or take. That's about the average weight of most cats.

The harpy eagle, native to Central and South America and one of the strongest eagles, primarily feeds on medium to large mammals. Sloth is a favorite food. The eagle's 3- to 4-inch talons have a grip strength estimated at 530 psi. It could break your bones.

Historically, the Haast's eagle, which lived in New Zealand until the 1500s, probably was the most formidable strengthwise. That bird had talons with a spread that could reach from your wrist to your elbow.