Raptors, the Sky Masters

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

A raptor’s eyes are huge compared to its body size; an eagle’s eyeballs are larger than an adult human’s. What’s more, each eye is far more densely packed with receptor cells in the fovea, the region in the retina that perceives color and sharpens images. We humans have about 200,000 visual cells per square millimeter of fovea; most raptors have about 1 million. And while humans have only one fovea in each eye, raptors have two.

One, called the “search” fovea, is located near the center of the retina and provides super-high-resolution monocular vision, allowing each eye to see to the side independently. The other, the “pursuit” fovea, is positioned on the retina’s outside curve. It works together with its counterpart in the other eye to give the bird binocular vision, allowing it to see directly forward and to perceive depth. Both visual abilities are essential for an airborne predator. A hawk high in the sky uses its high-res monocular vision to spot and keep a fix on prey as it dives (or, in raptor parlance, stoops), and applies its 3-D binocular vision to judge depth and distance as it closes within striking range or pursues a would-be escapee.

All things considered, a raptor’s signature fierce gaze seems more than justified. Actually, the birds get their glowering, serious look from the bony, feather-covered brows, known as supraorbital ridges, that shade their eyes and thus minimize glare.

MIRACLES OF FLIGHT

Most birds can fly, and a few can do it better than raptors in one particular way or another. Hummingbirds are the hands-down champions of maneuverability, for instance. But no other group of birds commands as wide and breathtaking a repertoire of aerial skills as raptors. A red-tailed hawk wheels high over a wheat field, its namesake tail flashing in the sun. An osprey plunges talons-first into a river and a heartbeat later lifts off, its powerful wings dripping and a wriggling fish in its grip. A prairie falcon dives bulletlike from 2,000 feet, then pulls into a long, stealthy glide inches above a meadow to blindside a ground squirrel.

Raptors’ wings, unlike airplanes’, are supremely flexible, instantly responsive to the shifting whims of the winds and to the wile and will of the pilot. Dozens of flight muscles enable the bird to alter the shape and position not only of its wings overall, but also of individual flight feathers. A hawk may fan its wings into broad planks to catch a ride on air currents, spread its fingerlike wingtips to stabilize, then suddenly collapse its wings to dive for prey. As it descends, the bird controls its direction, elevation and speed by flexing muscles here, adjusting feathers there.

Most raptors have massive flight muscles anchored to a large breastbone to power flapping flight. A few quick pumps can launch a 10-pound golden eagle skyward, its wings mocking gravity. A falcon on the hunt is a blur of wings beating 4½ times a second.

RSS | Comments | E-mail | Print