The next topic after birds’ eggs has to be the unusual behaviour of nesting birds. The whole physiology of nesting birds changes in a dramatic way. They move reluctantly and as if in slow motion. Their temperature rises and they don’t want to eat as much. Feathers ruffled, neck bent and the whole body puffed up into the shape of a ball, helps a nesting bird to keep its body temperature high and the eggs warm. In some birds (ducks, swans, chickens), the breast and lower body feathers become very soft and thick, and act as the best heat conductors and insulators. In many birds the underbelly is covered by a network of blood vessels and that keeps warmer the part of the body directly in contact with the newly-laid eggs. The task of sitting on eggs is often shared by both parents, if not in hours spent on the nest, at least in delivering food. Usually, it is a male that brings food to the nesting female and later feeds the young. The best providers in this respect are birds of prey. The birds’ population is at its leanest during the nesting season. There are other unusual characteristics of the nesting season. Almost all birds will ‘sit tight’ on the eggs even when a human or animal approaches the nest. Some birds pretend to be injured and will drag one wing on the ground, moving further away from the nest. But if attacked by the predator, they fly off at the speed of lightning. This method is used by smaller and generally non-aggressive birds, while big birds (swans and geese) never use deception – they simply attack instantly anyone approaching. Nesting periods vary from 14 days to nine weeks, and generally bigger birds nest longer than smaller ones. Of the various ways of nesting, the most interesting one is used by the largest penguins that inhabit the Antarctic. They start laying the eggs during the coldest period with the temperature down to minus 50 Celsius. Just before laying an egg, both parents develop a skin pouch, low on their tummies. The egg is kept warm there and each partner takes turns looking after the egg. The penguin has to stand for a long period holding the egg in the pouch until the partner comes back from the feeding trip and takes over. The egg is then exchanged by rolling it very carefully over the penguins’ feet to prevent any contact with ice.
Birds have a foolproof method of telling if their eggs are developing properly. Since the embryo inside an egg generates its own heat, an egg that is much cooler than the rest will give the parents clear indication as to which one is dead. In the last moment before hatching, the baby chick taps on the shell , then breaks a small hole, and with its first gulp of fresh air, starts squeaking to alert its parents. The female will immediately warm the baby, and the male will redouble his efforts to provide food for his family. The time of hatching is quite traumatic for baby chicks. The yolk sac, which until this time had been outside the embryo’s body inside the eggshell, enters its abdominal cavity, which until this point was open but will now close permanently. The yolk serves as a food reserve from which the baby feeds for at least the first 24 hours. When the time of hatching comes, the task of breaking a relatively strong shell-covered membrane could prove difficult for a young chick if it wasn’t for a special ‘tool’. It is a tiny, nail-like growth at the end of its beak. A ready-to-hatch chick needs to press this nail against the shell at the starting point, then moves his body systematically around the egg, making the same movements at various points, until he creates an opening line – a doorway to freedom. After serving its purpose, the little nail disappears within three days.
A baby chick always emerges from its shell very wet because at the point of hatching, the ‘waters break’. That is, a small balloon-like sac will burst and a drop of blood is spilled. A trace of blood in an empty eggshell is therefore a sure sign that the young bird has hatched successfully. Within seconds, the young chick dries out and sports masses of fluff. The mother’s feathers grease the fluff of her chick, and in the case of water birds, cover it in ‘talc’, making the young feathers waterproof, and the baby warm. The parents throw the shell fragments far away from the nest, and interestingly, flamingos eat the broken shell to their benefit. Not all chicks are born with masses of fluff. It depends on the parents’ nesting habits which divide birds into two major groups. The fluff soon wears off and proper feathers grow in its place.
At first, most birds cannot see very well or even at all because their eyes are covered by eyelids which only split into two and open after a few days. The wings of baby chicks are still not ready, but their feet are well-formed from the very beginning. Of all the baby bird’s organs, his digestive system is the best developed, starting with a big beak and ending at a protruding, large tummy. It seems in fact that the rest of the baby’s anatomy is just a collection of temporarily unimportant bits attached around and about the powerful digestive system. The beak, with its thick lips edged in bright yellow, has many nerve ends that are sensitive to the slightest touch. The inside of the mouth is also coloured boldly, either yellow or red. Its perimeter outlined by dark, symmetrically-placed spots to guide the parent’s beak. It is similar, in principle, to a pilot landing an aircraft within an exact space, pinpointed by the lights of the runway.