The Demands of the Egg
David Attenborough explores the extraordinary variety of ways in which birds from all over the world construct their nests and protect their eggs from predators. Because birds need to be light in order to fly, each egg must be laid as soon as it is produced and then kept both warm and protected. So the vast majority of birds make nests of some kind. Australian warblers use their beaks like a sewing machine to stitch leaves together, and apostle birds use them to trowel mud on their nests.