Precociality and altriciality

In the biology of birds and mammals, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. Precocial species are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. These categories form a continuum, without distinct gaps between them. In fish, this often refers to the presence or absence of a stomach: precocial larvae have a stomach at the onset of first feeding whereas altricial fish do not. Depending on the species, the larvae may develop a functional stomach during metamorphosis (gastric) or remain stomachless (agastric). The word is derived from the Latin root alere, meaning "to nurse, to rear, or to nourish" and indicates the need for young to be fed and taken care of for a long duration. By contrast, species whose young are immediately or quickly mobile are called precocial. The word "precocial" is derived from the same root as precocious, from the Latin root praecox, meaning early maturity in both cases. Extremely precocial species are called "superprecocial". Examples are the megapode birds, which have full-flight feathers at hatching and which, in some species, can fly on the same day they hatch from their eggs. Enantiornithes and pterosaurs were also capable of flight soon after hatching. Another example is the blue wildebeest, the calves of which can stand within an average of six minutes from birth and walk within thirty minutes; they can outrun a hyena within a day. Such behavior gives them an advantage over other herbivore species; they are 100 times more abundant in the Serengeti ecosystem than hartebeests, their closest taxonomic relative. Hartebeest calves are not as precocial as wildebeest calves and take up to thirty minutes or more before they stand, and as long as forty-five minutes before they can follow their mothers for short distances.

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Related concepts (18)

Megapode

The megapodes, also known as incubator birds or mound-builders, are stocky, medium-large, chicken-like birds with small heads and large feet in the family Megapodiidae. Their name literally means "large foot" and is a reference to the heavy legs and feet typical of these terrestrial birds. All are browsers, and all but the malleefowl occupy wooded habitats. Most are brown or black in color. Megapodes are superprecocial, hatching from their eggs in the most mature condition of any bird.

Heron

The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 72 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera Botaurus and Ixobrychus are referred to as bitterns, and, together with the zigzag heron, or zigzag bittern, in the monotypic genus Zebrilus, form a monophyletic group within the Ardeidae. Egrets do not form a biologically distinct group from herons, and tend to be named differently because they are mainly white or have decorative plumes in breeding plumage.

Cracidae

The chachalacas, guans and curassows are birds in the family Cracidae. These are species of tropical and subtropical Central and South America. The range of one species, the plain chachalaca, just reaches southernmost parts of Texas in the United States. Two species, the Trinidad piping guan and the rufous-vented chachalaca occur on the islands of Trinidad and Tobago respectively. The family Cracidae was introduced (as Craxia) by the French polymath Constantine Samuel Rafinesque in 1815.