The Life Collection

The Demands of the Egg (6x8)

Air date: Dec 09, 1998

This episode explores the lengths to which birds will go to ensure that their chicks are brought into the world. Attenborough begins on an island in the Seychelles, where sooty terns, which have hitherto spent their lives on the wing, have landed to lay their eggs. This is a necessity for birds, as eggs are too heavy to be borne in the air for any considerable length of time. It is imperative that nests are kept as far away from predators as possible, and unusual locations for them are shown, such as: behind the water curtain of Iguazu Falls in South America (as chosen by swifts), cliffs on Argentina's coast favoured by parrots, an ants' nest occupied by a woodpecker, and a tree hole inside which a female hornbill seals itself. Eggs require warmth, and some nests are insulated by the owners' feathers, others from ones found elsewhere. External temperatures dictate how the eggs are incubated. The snowy owl has to do so itself, because of its habitat; however, the maleo is able to take advantage of solar heating. The amount of eggs laid also varies: for example, the kiwi lays just one, whereas the blue tit will deposit many. Their mottled surface serves to camouflage them. Birds that steal eggs include toucans and currawongs. A number of strategies are employed to deter the thieves, as illustrated by the yellow-rumped thornbill, which builds a decoy nest atop its actual one, and the plover, which distracts marauders by feigning injury.