Zebra black and white at birth. Plains and mountain zebra foals are protected by their mothers, as well as the head stallion and the other mares in their group. Grévy's zebra foals have only their mother as a regular protector, since, as noted above, Grévy's zebra groups often disband after a few months. Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. While occasionally successful, most of these attempts failed due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between
Plains zebra plains zebra. One of which is its distinctive, high-pitched, contact call (commonly called "barking") heard as "a-"ha", a-"ha", a-"ha"" or "kwa-ha, kaw-ha, ha, ha" (video), also transcribed as "kwahaah", or "oug-ga". The species name "quagga" is derived from the Khoikhoi word for "zebra" and is onomatopoeic for its call. When a predator is sighted, a zebra makes a two-syllable alarm call. A loud snort is made when moving in cover of potential danger. When in contentment, a zebra makes a more drawn-out snort. Males make a short, high-pitched squeal when hurt, and foals emit a drawn-out wail when in distress.