Science Fair Project Encyclopedia
The distinction between precocial and altricial species is particularly sharp in birds. Precocial birds, including many ground-nesting species, have offspring that are born covered with down and ready to leave the nest in a short period of time following hatching (e.g. 24 hours). This amount of time is neccessitated by the fact that offspring need time for their downy coats to dry prior to leaving the nest. Additionally, most precocial chicks lack the ability to control their own body temperatures (thermoregulation), and they depend on the attending parent(s) to provide an outside source of heat for a short period of time. Examples or precocial birds include the domestic chicken, many species of ducks and geese, and rails and crakes.
Precociality is of course also found in other groups. Familiar examples of precocial mammals are most ungulates, the guinea pig, and most species of hare. This last example demonstrates that precociality is not a particularly conservative characteristic, in the evolutionary sense, since the closely related rabbit is highly altricial.
Precocial species typically have a longer gestation or incubation period than related altricial species, and smaller litters or clutches, since each offspring has to be brought to a relatively advanced (and large) state before birth or hatching.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details