The animal on the cover of Learning JavaScript, Second Edition, is a baby black, or hook-lipped, rhinoceros (Diceros bicornis). The black rhino is one of two African species of rhinos. Weighing up to one and a half tons, it is smaller than its counterpart-the white, or square-lipped, rhinoceros. Black rhinos live in savanna grasslands, open woodlands, and mountain forests in a few small areas of southwestern, south central, and eastern Africa. They prefer to live alone and will aggressively defend their territory.

With an upper lip that tapers to a hooklike point, the black rhino is perfectly suited to pluck leaves, twigs, and buds from trees and bushes. It is able to eat coarser vegetation than other herbivores.

Black rhinos are odd-toed ungulates, meaning they have three toes on each foot. They have thick, gray, hairless hides. Among the most distinctive of the rhino's features is its two horns, which are actually made of thickly matted hair rather than bone. The rhino uses its horns to defend itself against lions, tigers, and hyenas, or to claim a female mate. The courtship ritual is often violent, and the horns can inflict severe wounds.

After mating, the female and male rhinos have no further contact. The gestation period is 14 to 18 months, and the calves nurse for a year, though they are able to eat vegetation almost immediately after birth. The bond between a mother and her calf can last up to four years before the calf leaves its home.

In recent years, rhinos have been hunted to the point of near extinction. Scientists estimate that there may have been as many as a million black rhinos in Africa 100 years ago, a number that has dwindled to 2,400 today. All five remaining species, which include the Indian, Javan, and Sumatran rhinos, are now endangered. Humans are considered their biggest predators.

The cover image is from Cassell's Natural History. The cover font is Adobe ITC Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSansMonoCondensed.