size of their home ranges differ according to sex, age and
the type of habitat, with immature animals usually occupying
larger areas than adults. The only time they gather in groups
is temporarily to wallow: five is the largest party usually
seen together, though groups of as many as 13 have been recorded.
Although aggression between bulls is normal, they tend to
actively avoid contact: sometimes serious fighting does occur,
however, particularly over females in oestrus. Snorting and
pawing are the prelude to a series of short charges, which
will usually stop about 6 m (20 ft) short of impact. However,
during a time of ecological stress in East Tsavo, before the
drought in 1960/1, all the rhino were found to be wounded
and some were killed in fights. This was evidently abnormal
behavior produced by conditions of extreme hardship.
During the day they retire to the shade of thickets to sleep,
either standing or lying with their legs curled under them.
Black rhinos sometimes sleep lying flat on their sides; a
position never adopted by the white rhino.
The black rhino seems to take a particular delight in crashing
through cover; unlike the other animals of the bush in that
it has no regular predators as an adult, it has no need to
move stealthily. Like the white rhino the black rhino sprays
urine and dung; it also leaves a scented trail consisting
of flakes of mud and pieces of dead skin by rubbing against
trees: this helps to communicate its presence, and possibly
its identity, to the next rhinoceros who comes along.
Feeding in the morning and evening and sleeping in the heat
of the day, the species has become largely nocturnal in most
parts of its range. This is most likely the result of natural
selection, which has eliminated the more diurnal individuals
which were most likely to be shot. Wallowing plays an important
part as it helps to lower body temperature, offers protection
against biting insects when the mud dries, and helps with
'rhino sores', which are areas of cracked and often inflamed
skin which occur most commonly in the hollow behind the elbows
of the front legs.