african bark black coats black skin Bray common zebra equids erect manes fast grant’s zebra grazers harems herbivores herbivorous herd herds individual mammal mohawk-like manes patterns plains zebra social stiff manes stripes ungulates unique white fur white stripes zebra black-&-white black-coats black-skin common-zebra erect-manes grant’s-zebra mohawk-like-manes plains-zebra stiff-manes white-stripes greyscale monochrome gray grey patterned barking braying Camouflage contrast contrasting equus-quagga-boehmi family-groups mammals subspecies unique-stripe-patterns white-fur