The Trials of Life

This programme surveys the methods employed in attracting a mate, mainly those of birds. The Indian florican inhabits long grass, and so is difficult to see. In order to gain attention, it 'trampolines' in the same spot for up to 400 times a day. Whales sing to their prospective partners, and the female's calls can be heard by suitors for over eight kilometres. When animals send out signals of attraction, they must also ensure that they don't entice the wrong species, and so have markings that differ prominently. Attenborough highlights the booby as an example: there are around half a dozen species, all of which may occupy the same island. However, the blue-footed booby reassures its chosen mate by continually lifting its feet. Tropicbirds and marsh harriers are shown providing graceful aerobatic displays, while the sac-winged bat uses a strong perfume to lure a companion. Among those birds that produce the most spectacular visual displays are the lyrebird (which also has an elaborate song), the peacock, and the riflebird (and indeed most other birds of paradise). The bowerbird invites potential partners to inspect its bower: a specially prepared area that contains a hut or walkway augmented by strikingly coloured objects. The intricate dances performed by manakins in Trinidad are also examined. Finally, Attenborough observes the topi's display courts, whose sharply defined boundaries are jealously guarded by rival males.

This installment investigates the ways in which those animals that live in social groups interact with each other. The solitary eagle is contrasted with whooper swans landing in Scotland after a 1,600-kilometre journey from Iceland. Once arrived, they must battle for territory with those already there, and pairs or families are usually victorious. Attenborough uses a group of farmyard chickens to demonstrate a pecking order. A pride of lions is shown co-operating to subdue a buffalo. Afterwards, each animal peacefully awaits its turn at the carcass. Baboons live in troops of up to 150, and their complex dominance hierarchy is examined in detail. Vampire bats display mutual assistance by regurgitating blood for any neighbour that has missed out on a night's feeding. Dwarf mongooses live in family groups of around a dozen. While some look for food or sleep, others are always posted on the lookout for predators and quickly raise the alarm if necessary. Meanwhile, some of the most extreme co-operation is demonstrated by the underground naked mole rat, whose 80-strong clusters are divided into workers (who tunnel perpetually), soldiers (who only act when danger threatens), and a single queen for breeding. Leafcutter ants are shown transporting their food deep below ground: it has to be planted in a special fungus to remove its indigestible cellulose, and each stage of the operation is carried out by a different caste of individuals.

This episode focuses on those species that co-operate and depend on (or exploit) others. Spotted deer follow langur monkeys as they travel from tree to tree, eating any leaves that get dropped from above. In return, the deer serve as a lookout when the primates are feeding on the ground. Underwater, a hermit crab is shown adding sea anemones to its shell in order to protect itself from attack by an octopus, and a goby assists a virtually blind shrimp. Fleas, lice and mites are parasites: they share no mutual partnership and instead take advantage of creatures for food or shelter. However, parasites have their predators, and an example are the finches of the Galápagos Islands that clear the resident giant tortoises of their ticks, and oxpeckers, which do the same for giraffes in Africa (and even use its fur to line their nests). Some fish regularly clean others, and wrasse and shrimp appear to specialise in this regard, as do remora, which permanently hang on to their hosts. One parasite that grows inside its host is the fluke, and one is shown gestating inside a snail, having previously been unknowingly eaten. Because it needs to transfer to a bird's gut to develop further, it causes the snail to advertise its presence to allow itself to be consumed - thus completing the circle. However, some microscopic creatures inhabit the stomachs of large herbivores in order to break down the cellulose of their diet, thereby aiding their digestion.

This programme explores forms of navigation. Attenborough starts in Africa at dusk, by describing some of the species that don't rely on sight. The spotted hyena uses its acute sense of smell to guide it while it hunts nocturnally, while galagos urinate on their hands so they can completely mark their movements. Some animals use echolocation and these include swiftlets, bats and river dolphins. By contrast, electric eels use fields of electricity to sense their environment. During the hours of daylight, other methods are employed: the rufous elephant shrew, with its carefully cleared network of pathways, has a sharp mental picture of its habitat - even knowing the various shortcuts with which to evade capture. Attenborough visits the Sahara to illustrate a species that makes the longest overland journey of any insect: cataglyphis, an ant that uses the sun's position to enable it to return to its nest in a straight line. Lobsters in the Bahamas are shown marching in columns to escape stormy waters. In its search for perpetual daylight in which to fish, the Arctic tern makes a 19,000-kilometre journey from one end of the Earth to the other. The albatross is highlighted as one of the most skilled navigators: it can travel up to 1300 kilometres over sea in search of food for its chicks, and still find its way back to the nest. Finally, Attenborough stands on a waterfall in Ireland to tell of the three-year, 10,000-kilometre journey made by elvers.

The next installment is devoted to the ways in which animals gather their sustenance. Attenborough begins in the South American rainforest, where the proliferation of animal and plant life does not necessarily make it easy to find food. Some leaves are poisonous, and so those that eat them have to be careful. Other plants use food (or nectar) as a bribe to get their pollen transported, and several species of hummingbird have developed exclusive relationships with certain of them. Fruit is also on offer, again as a means of reproduction, and creatures such as squirrel monkeys eat little else. Meanwhile, parrots and macaws take kaolin as an antidote to their diet of toxic seeds. Attenborough witnesses a 60,000 strong flock of knot and dunlin suddenly take advantage of a low tide to feed on tiny mud-dwelling molluscs. Barracuda hunt small fish, and drive shoals of them into bays to be eaten by pelicans, which are besieged by gulls that attempt to steal their catches. One species of gecko is able to differentiate between worker termites and the more dangerous soldiers. The web of the orb spider is hailed as one of the most elegant food catching devices, and the methods of two others, nephila and its kleptoparasite visitor, argyrodes, are explored in detail. Finally, tropicbirds, their crops full with food en route back to their nests, are ambushed in mid-air by a group of frigatebirds, whose aim is to make them surrender their cargo.

The first episode examines the various methods by which creatures come into the world. Attenborough’s opening statement alludes to the annual spawning of the Christmas Island red crab, of which there are estimated to be some 120 million. The exercise is all the more hazardous since the species is a land crab, and the eggs have to be deposited in the sea - where the most ancient animals on the planet still live and breed. One of the most prolific aquatic egg producers is the giant clam, but some land animals also lay vast quantities, and the mantis is one example. In the Western United States, Attenborough observes a wasp that digs a burrow, conceals it, and stocks it with fresh caterpillars for her emerging young. The grubs of another start life inside caterpillars, and eat the unsuspecting hosts. The problems of larger animals are illustrated by snow geese in the Arctic, which have to defend their eggs from arctic foxes. The process of embryonic growth inside the egg, from laying to hatching, is shown in detail. The malleefowl warms its eggs with rotting leaves, and Attenborough demonstrates the care with which it regulates them by adding sand to its mound - to have it kicked back in his face. The sea louse is a crustacean that commits suicide: its grubs consume so much of the mother’s energies that she dies after birth. Mammals shown giving birth to fully formed young include wildebeest, antelope, sea lions and chinchillas.