Birds that are precocial-meaning that when they hatch their eyes are open, they have down feathers, and are immediately mobile-will leave the nest within a few hours, up to two days. Examples are ducks, turkeys, and quail. These type birds usually nest on the ground. Birds that are altricial -- meaning that when they hatch their eyes are usually not open, they have no down feathers, are relatively immobile, and are completely dependent on their parents -- will stay in the nest for as long as 270 days. Examples are owls, robins, hawks, woodpeckers, cranes, parrots, and songbirds.
Days in the nest from hatching until fledging: House Sparrow: 12 days Peregrine Falcon: 40 days Pigeon: 30 days American Robin: 13 Wandering Albatross: 270 days Mourning Dove: 15 days Purple Martin: 29 days Chimney Swift: 30 days Bald Eagle: 84 days Cooper's Hawk: 34 days Allen's Hummingbird: 25 days Black-crowned Heron: 49 days Blue Jay: 21 days Downy Woodpecker: 21 days
Even within species, fledging times vary. Large broods tend to fledge earlier than when there are only one or two baby birds in the nest. Food supply and weather conditions change also alter the fledging times by a few days. All baby birds in the same nest may not fledge at the same time; the largest may fledge several days earlier than the smallest.
If you find a baby bird on the ground, try to determine if it is a nestling or a fledgling. If it can perch or firmly grip your finger, it is probably a fledgling. Do not try to put it back in its nest. It has probably just fledged, and its parents are usually nearby to help it. If it is unable to perch, it may have fallen out of its nest. Look nearby for its nest and gently return it.