dense with small ranges, or migratory, being less populated with separate, extensive dry and wet home ranges. When migrating, zebras appear to rely on some memory of the locations where foraging conditions were best and may predict conditions months before their arrival. Diet and predation Plains zebras primarily feed on grass; preferred species being Themeda triandra, Cynodon dactylon, Eragrostis superba and Cenchrus ciliaris. Zebra sometimes browse or dig for corms and rhizomes during the dry season. They appear to partial to eating scorched Colophospermum mopane and Pterocarpus rotundifolius, consuming both the leaves and twigs. Plains zebras are adapted for grazing on both long, tough grass stems and newly emerging short grass. In some areas, it rarely feeds below to ground level. It ranges more widely than many other species, even into woodlands, and it is often the first grazing species to appear in a well-vegetated area. The flexible upper lip allows them to push plant material between the incisors to cut. Zebras have a less efficient digestive system than ruminants but food passage is twice as fast. Thus, zebras are less selective in foraging, but they do spend much time eating. The zebra is a pioneer grazer and prepares the way for more specialised grazers such as blue wildebeests and Thomson's gazelles. The plains zebra's major predators are lions and spotted hyenas. Lions are most successful when targeting lone individuals, usually an old male while hyenas chase and isolate an individual from the group, usually a female or foal. Nile crocodiles also prey on zebras when they are near water. Less common predators include cheetahs and African wild dogs, which mostly hunt foals. When in the presence of a lion, zebras remain alert and stand in a semi-circle at as much as and no less than . Stallions sometimes try to drive lions away with bluff charges. By contrast, zebras may approach cheetahs and wild dogs and a single hyena is allowed to come within a few metres. To escape from predators, an adult zebra can run at . When being hunted by hyenas or wild dogs, a zebra harem stays close together and cooperates to protect threatened members, particularly the young. The harem stallion goes on the offensive and attacks the dogs or hyenas. Behaviour Plains zebras are nomadic and non-territorial, home ranges vary from to , depending on the area and if the population is migratory. They are