Two types of baby birds

Baby birds that hatch with their running shoes on are called precocial. Precocial means "ripened beforehand." (The word comes from the same Latin source as "precocious.") They hatch with their eyes open, and as soon as their downy feathers dry, they start scurrying about, following their parents and searching the ground for something to eat. Other precocial birds, like the killdeer, are chickens, ducks, and quail. None of these precocial babies lies in the nest and gets waited on.

Birds that hatch blind, naked, and helpless are called altricial, which comes from a Greek word meaning "wet nurse." Robins are altricial, as are blue jays, cardinals and most other birds. The hatchlings lie helplessly in their nests, relying utterly on their parents to bring them food and push it down their throats. It's two weeks or more before they mature enough to leave the nest, and even after they leave it, their parents are still feeding them.

Precocial birds stay in the egg twice as long as altricial birds, so they have more time to develop. A one-day-old killdeer chick is actually two weeks older than a one-day-old robin nestling. Although adult robins and killdeer are the same size, a killdeer's egg is twice as big as a robin's. There's more nourishment built into the killdeer egg, to sustain the embryo for its longer time in the shell. ~ https://www.birdwatching.com/stories/killdeer.html

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