Broadcast 4 December 2002, the next instalment looks at herbivorous mammals. The sloth is a leaf-eater, but it has compensated for the lack of nutriment in its diet by doing less (its reactions are a quarter the speed of a human's). This doesn't apply to all herbivores, which rely on bacteria in their stomachs to digest the leaves' cellulose. Plants can be poisonous, but Brazilian tapirs — the largest inhabitant of the South American rainforest — deal with them by eating a little of each species and then supplementing it with kaolin. In East Africa, via infrared cameras, Attenborough observes a herd of elephants squeezing into a pitch black cave and gouging the walls with their tusks to mine salt for their diet. Grazing animals, such as caribou and wildebeest, must migrate at the onset of winter and make long journeys to find new pastures. Despite its spiny fortification, the acacia is favoured by antelope, elephants and giraffes, which all have adaptations to reach its leaves. Smaller grazers are always at risk from carnivores: so they have developed the means to detect and evade them, and do so more often than may be supposed. A herd of wildebeests is shown defending one of their number by charging the lions attacking it. However, the horns of antelope are primarily used for fighting each other to determine rank within their group and to maintain a breeding ground. Topi are shown doing so to the point where they are so exhausted that they easily succumb to a pack of hyenas.
The Life of Mammals is a BBC nature documentary series written and presented by David Attenborough, first transmitted in the UK from 20 November 2002. A study of the evolution and habits of the various mammal species, it was the fourth of Attenborough's specialised surveys following his major trilogy that began with Life on Earth. Each of the ten episodes looks at one (or several closely related) mammal groups and discusses the different facets of their day-to-day existence. All the programmes are of 50 minutes' duration except the last, which extends to 59 minutes. The series was produced in conjunction with the Discovery Channel. The executive producer was Mike Salisbury and the music was composed by Dan Jones and Ben Salisbury. It was later shown on Animal Planet. Part of David Attenborough's 'Life' series, it was preceded by The Life of Birds (1998), and followed by Life in the Undergrowth (2005). However, in between the former and this series, David Attenborough presented State of the Planet (2000) and narrated The Blue Planet (2001).