White rhinos have a distinctive broad, straight mouth which is used for grazing. Its ears can move independently to pick up sounds, but it depends most of all on its sense of smell. The olfactory passages that are responsible for smell are larger than their entire brain. The white rhinoceros has the widest set of nostrils of any land-based animal. The genome size of the white rhinoceros is 2666.62 Mbp. A diploid cell has 2 x 40 autosomals and 2 sex chromosomes (XX or XY). White rhinoceroses are found in grassland and savannah habitat. Herbivore grazers that eat grass, preferring the shortest grains, the white rhinoceros is one of the largest pure grazers. It drinks twice a day if water is available, but if conditions are dry it can live four or five days without water. It spends about half of the day eating, one third resting, and the rest of the day doing various other things. White rhinoceroses, like all species of rhinoceros, love wallowing in mud holes to cool down. The white rhinoceros is thought to have changed the structure and ecology of the savanna's grasslands. Comparatively based on studies of the African elephant, scientists believe the white rhino is a driving factor in its ecosystem. The destruction of the megaherbivore could have serious cascading effects on the ecosystem and harm other animals. White rhinoceroses produce sounds which include a panting contact call, grunts and snorts during courtship, squeals of distress, and deep bellows or growls when threatened. Threat displays (in males mostly) include wiping its horn on the ground and a head-low posture with ears back, combined with snarl threats and shrieking if attacked. The vocalizations of the two species differ between each other, and the panting contact calls between individual white rhinoceroses in each species can vary as well. The differences in these calls aid the white rhinoceroses in identifying each other and communicating over long distances. The white rhinoceros is quick and agile and can run . White rhinoceroses live in crashes or herds of up to 14 animals (usually mostly female). Sub-adult males will congregate, often in association with an adult female. Most adult bulls are solitary. Dominant bulls mark their territory with excrement and urine. The dung is laid in well-defined piles.