Chicks begin pipping (breaking their shells) about 24 to 48 hours before hatching.
The chick breaks through the shell using a growth on its bill called an "egg tooth". The egg tooth is not a true tooth and falls off soon after hatching.
Chicks hatch with their eyes open and are covered with a long, thin coat of white, buff, or grayish down.
Newly hatched chicks are relatively helpless and unable to stand.
Care of Young
In most species, the female continues to care for the young while the male continues to catch all the prey. One study found that a male osprey provided about two to three fish per day during incubation and up to six fish per day by the time the chicks left the nest (Newton, 1979).
When the chicks are first hatched, the female broods (sits on or over the young) almost continually. In most species, the female feeds the chicks by tearing off small pieces of flesh from prey provided by the mate. In a few species, such as Old and New World vultures and secretary birds, food is regurgitated to the young.
As the chicks get older the female broods less, but stays near the nest. The young are gradually fed more and more parts of the prey.
When the chicks are fully feathered (fledged) and can eat whole prey themselves, the female spends more time away from the nest hunting for herself and her young.
Once the young are able to fly, some parents show their young how to hunt. Cooper's hawk and peregrine falcon parents have been observed leading their young on rapid chases before giving up their prey. These same parents may also release still-living prey for their young to catch and kill.
Chick Growth & Development
Because chicks of the same clutch hatch over several days, the older, larger chicks are better able to compete for food. As a result, the youngest chick(s) in the nest often dies of starvation or is killed by a larger nest mate. Scientists believe asynchronous hatching is an adaptation to unpredictable food supplies. If food is plentiful, all the chicks survive. If food is scarce, the brood is rapidly reduced.
The nestling period (the time from hatching to fledging, when a bird is able to fly) lasts from four to seven weeks. As with incubation, large species have proportionately longer nestling periods than small species.
Chicks gain weight slowly at first, then increase rapidly, leveling off around the time of fledging.
Small species grow more rapidly than large species. Small species may reach adult weight by fledging, while large species may not reach adult weight until sometime after leaving the nest.
As contour feathers replace downy ones, chicks begin to preen after meals.
Once wing feathers have developed, chicks spend a considerable amount of time flapping them at the nest.
Postfledging periods (the period between fledging and complete independence) range from two to three weeks in small falcons, five to ten weeks in Buteo hawks, and up to several months in large eagles and vultures.
After fledging, young birds begin to make short flights to nearby trees or perching sites. They usually return to the nest when a parent returns with food.
Later, the young may intercept a parent further and further away from the nest, sometimes screaming loudly or even attacking the parent for food.
When the fledglings can hunt independently, they may leave the nest area on their own or wait until the parents stop feeding them, drive them away, or leave to migrate.
