The word “precocial” is derived from the same root as precocious, implying in both cases early maturity .The span between precocial and altricial species is particularly broad in birds. Precocial birds are born with their eyes open. They are covered with downy feathers that soon grow to adult feathers after hatching. Birds of this kind can also swim and run much sooner after their birth than other birds, such as songbirds. Very precocial birds can be ready to leave the nest in a short period of time following hatching (e.g. 24 hours). Many precocial chicks are not independent in thermoregulation (the ability to regulate their own body temperatures), and they depend on the attending parent(s) to brood them with body heat for a short period of time. Precocial birds find their own food, sometimes with help or instruction from the parents. Examples of precocial birds include the domestic chicken, many species of ducks and geese, waders, rails and the hoatzin. The most extreme, superprecocial birds are certain species of the megapodes, where the newly hatched chicks dig themselves out of the nest mound without parental assistance, and are capable of flight on the same day they hatch.
In bird and mammal biology, altricial species are those species whose newly hatched/born young are relatively immobile, lack hair or down, are not able to obtain food on their own, and must be cared for by adults; closed eyes are common, though not ubiquitous. Altricial young are born helpless and require care for a specific amount of time. Among birds, these include herons, hawks, woodpeckers, owls, cuckoos and most passerines. Among mammals, marsupials and most rodents are altricial. Cats, dogs, and humans are some of the best-known altricial organisms.