viernes, 18 de marzo de 2011
Zebras, horses and wild asses are all equids, long-lived animals that move quickly for their large size and have teeth built for grinding and cropping grass. Zebras have horselike bodies, but their manes are made of short, erect hair, their tails are tufted at the tip and their coats are striped.
Three species of zebra still occur in Africa, two of which are found in East Africa. The most numerous and widespread species in the east is Burchell's, also known as the common or plains zebra. The other is Grevy's zebra, named for Jules Grevy, a president of France in the 1880s who received one from Abyssinia as a gift, and now found mostly in northern Kenya. (The third species, Equus zebra, is the mountain zebra, found in southern and southwestern Africa.)
The long-legged Grevy's zebra, the biggest of the wild equids, is taller and heavier than the Burchell's, with a massive head and large ears.
Zebras have shiny coats that dissipate over 70 percent of incoming heat, and some scientists believe the stripes help the animals withstand intense solar radiation. The black and white stripes are a form of camouflage called disruptive coloration that breaks up the outline of the body. Although the pattern is visible during daytime, at dawn or in the evening when their predators are most active, zebras look indistinct and may confuse predators by distorting true distance.
The stripes on Grevy's zebras are more numerous and narrow than those of the plains zebra and do not extend to the belly. In all zebra species, the stripes on the forequarters form a triangular pattern; Grevy's have a similar pattern on the hindquarters, while others have a slanted or horizontal pattern.
Burchell's zebras inhabit savannas, from treeless grasslands to open woodlands; they sometimes occur in tens of thousands in migratory herds on the Serengeti plains. Grevy's zebras are now mainly restricted to parts of northern Kenya. Although they are adapted to semi-arid conditions and require less water than other zebra species, these zebras compete with domestic livestock for water and have suffered heavy poaching for their meat and skins.
Family groups are stable members maintaining strong bonds over many years. Mutual grooming, where zebras stand together and nibble the hair on each other's neck and back, helps develop and preserve these bonds. Family members look out for one another if one becomes separated from the rest, the others search for it. The group adjusts its traveling pace to accommodate the old and the weak.
The females within a family observe a strict hierarchical system. A dominant mare always leads the group, while others follow her in single file, each with their foals directly behind them. The lowest- ranking mare is the last in line. Although the stallion is the dominant member of the family, he operates outside the system and has no special place in the line.
Zebras are avid grazers. Both Burchell's and Grevy's zebras are in constant search of green pastures. In the dry season, they can live on coarse, dry grass only if they are within a short distance (usually no farther than 20 miles away) of water holes.see more at what do zebras eat.