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The animal on the cover of Learning PHP is an eagle. Eagles fall into the category of bird known as “raptors,” a category that also includes falcons and hawks. There are two types of raptor: grasping killers, with beaks shaped for tearing and cutting, and short toes with curved claws designed for killing; and grasping holders, with beaks shaped for tearing and biting, and longer toes designed for holding. Eagles are grasping killers. Sea eagles have special adaptations to their toes that enable them to grasp smooth prey such as fish. Their excellent vision enables all eagles to spot prey from the air or a high perch. The eagle then swoops down, grabs its prey, and takes off in flight again, in one graceful movement. Eagles often eat their victims while still flying, breaking them apart and discarding the nonedible parts to lighten their load. Eagles, like most raptors, often dine on sick or wounded animals.

There are more than 50 species of eagle spread throughout the world, with the exception of New Zealand and Antarctica. All species of eagles build nests, known as aeries, high above the ground, in trees or on rocky ledges. A pair of eagles will use the same nest year after year, lining it with green leaves and grass, fur, turf, or other soft materials. The eagle will add to its nest each year. The largest eagle nest ever found was 20 feet deep and 10 feet across.

Hunting, increased use of pesticides, and the diminishment of their natural environment, with the attendant reduction in food sources, have endangered many species of eagle.

Many of the animals on O’Reilly covers are endangered; all of them are important to the world. To learn more about how you can help, go to animals.oreilly.com.

The cover image is a 19th-century engraving from the Dover Pictorial Archive. The cover fonts are URW Typewriter and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.