Gary Holt, age 11, of Chattanooga, Tenn., for his question:
DO ALL BIRDS HATCH FROM EGGS?
All birds hatch from eggs. Birds are found in all parts of the world and they have many different ways of life. The number of eggs they lay also varies greatly.
Most wild birds lay from four to eight eggs each year, although the large California condor that has almost become extinct lays only one. A few wild birds lay up to 20 eggs each year. The domestic birds, such as chickens and duck, may lay 350 or more eggs a year.
The yolk or yellow part of the egg provides much of the early food that nourishes the young bird before it hatches. A small cluster of cells on the yoke make up the germ from which the young bird develops.
The yolk floats in the albumen, or white of the egg, which is also food for the developing bird. The yolk and albumen are inside a hard shell that is lined with a thin, tough skin.
Wild birds whose eggs are laid in holes in the ground or other sheltered places are likely to have eggs with pure white shells. Birds that nest on top of the ground or those that build nests that are not covered usually lay colored eggs.
Eggs usually are hatched by the warmth of the adult birds' bodies. To hatch, the eggs must be kept at a temperature of about 99.5 degrees Fahrenheit.
Some female birds sit on their eggs for 20 or 30 minutes at a time and then leave the nest to eat. Male birds sometimes sit on the eggs when the female leaves them. Other males feed the females sitting on the eggs. In some species, only the male birds sit on the eggs.
Some birds come out of the egg fully feathered and able to see and run. They take longer to hatch than birds that are less developed when they emerge. Some are born naked and others are born covered with down, or soft feathers.
Sparrow eggs hatch in about 12 days and chicken eggs in 21 days. An ostrich egg, the largest of all, takes six weeks to hatch. The egg of the emperor penguin takes 60 days.
Quail, sandpipers and other game birds can run a few hours after they come out of the shell. Ducklings are able to take to the water when they are only one day old.
But baby songbirds, woodpeckers, hawks and parrots are blind and helpless when they hatch. They must stay in the nest until their eyes open and their feathers grow. The parents feed the babies and keep them warm. Some birds that are born helpless can crawl out of the nest when they are about eight days old. Baby meadow larks and red winged blackbirds often play in the reeds and grasses around the nest.
Most small birds spend 12 to 14 days at home, but some woodpeckers stay for at least a month. The young of large birds, such as the California condor, may spend as long as six months in their nests.
Some birds, such as cowbirds, do not raise their own young. They lay their eggs in the nests of other birds.