The development of birds can be classified into one of two main types: precocial and altricial. Precocial birds, like chickens, ducks and owls, hatch out with a warm covering of down feathers. A precocial chick can keep its body reasonably warm in the absence of heat from an incubating parent. Some precocial chicks can feed themselves soon after hatching. A Lesser Scaup duckling can swim, dive and catch fish only three days after hatching. Others, like gulls and terns, depend on their parents for food.
Precocial chicks are quite mobile on the ground or in the water soon after hatching. However, it takes a good bit of time, often a couple of months, before they are able to fly. Parents of precocial chicks must spend a fair amount of time watching out for predators looking to make a flightless chick into a meal.
After a period of time, a precocial chick learns to fly. The act of taking the first flight is called fledging. The amount of care given to precocial chicks before and after fledging varies. Sandpipers, like the Semipalmated Sandpiper, leave their flightless young on the arctic tundra and begin their migration southward. The young, with the abundant supply of insects on the tundra in the summer, can fend for themselves. Ultimately, the sandpiper chicks fledge and, guided by a remarkable navigational sense, follow on the heels of the parents two or three week later. Canada Geese tend their young throughout the nestling and fledging periods. The families migrate south together.
Altricial development, the other major developmental type in birds, is characteristic of all songbirds, woodpeckers, swifts, kingfishers, pigeons and hummingbirds. The young hatch as helpless, naked birds. Their eyes are not open and they are unable to even hold their heads up. The young hatchlings cannot maintain their body temperature by themselves for even a short period of time. As a result, one of the parents must incubate the young to keep them warm. This incubation, usually done by the mother, is made possible by the presence of a brood patch on the underside of the body. This brood patch has no feathers and has a rich supply of blood vessels to allow the quick transfer of heat from the parent to the young.
The young must be fed by the adults and rapidly begin to add weight and feathers. The incubation period in most songbirds lasts between eleven and fourteen days. The mother has to spend less and less time incubating the young as they grow as their feathers develop. By the time the nestling period is ending, the chicks have voracious appetites that often tax the abilities of the parents to provide food.
After the nestling period, the young are ready to fledge. The work of the parents is not over although the nest is abandoned once the young fledge. The fledglings follow their parents around are still fed by the parents. You can see the begging behavior of recently fledged young at your feeder. After a period of two or three weeks, the fledglings have become proficient fliers and good foragers so the family unit breaks down. The fledglings are now on their own.
So which is better, precocial or altricial development? Precocial development has the advantage of reducing the time spent in incubating the nestlings as the chicks are born with a covering of down. Precocial chicks can find much of their own food, freeing the parents from an additional energy drain. However, the time to fledging takes a long time. From hatching to fledging for a Ruffed Grouse takes over two months. Hawks and owl chicks may take three months or more to fledge. That’s a long time to avoid predators without the benefit of flying.
Altricial development presents a tremendous challenge for the parents. After hatching, the young have to be fed and incubated. However, the development is quite rapid. After hatching, the young can be fledged and independent in less than a month. In fact, some of our songbirds like House Wrens and Eastern Bluebirds will even have two broods of young in a single season.
The tradeoff then is for parents to work really hard for a relatively short period of time (altricial development) or invest less energy in tending the young on a daily basis but have young which are at risk from predators for a long time because they take so long to fledge (precocial development).
[First published July 25, 2009]