Birds — the untold class in the middle of terrestrial vertebrates at the present time there are about nine thousand species. Representatives of the class vserasprostraneny extensively around the world and different friend from each other in appearance, voice, habits. Some of them even lost the ability to fly. But one thing unites them voedinyzhdy — all the birds and feathered breed, laying eggs. On this and it will be in the fourth film of the BBC. What is the bird's egg, why the female seeks as quickly as possible to demolish it, as in birds formed a family and almost everything else in the documentary film "Life Birds "