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Precociality and altriciality

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States of newborn mobility and independence

A diagram of altricial and precocial bird species

Precocial (/prɪˈkəʊʃəl/) species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. Altricial species are those in which the young are underdeveloped at the time of birth, maturing with the aid of their parents. These categories form a continuum, without distinct gaps between them.

A young chick stands up. Chickens are precocial birds and can stand shortly after hatching.<br>In fish, this often refers to the presence or absence of a stomach: precocial larvae have one at the onset of first feeding whereas altricial fish do not.[1] Depending on the species, the larvae may develop a functional stomach during metamorphosis (gastric) or remain stomachless (agastric).

Altricial young birds<br>California quail chick (Callipepla californica), a precocial chick

Precociality<br>[edit]

Precocial young have open eyes, hair or down, large brains, and are immediately mobile and somewhat able to flee from or defend themselves against predators. For example, with ground-nesting birds such as ducks or turkeys, the young are ready to leave the nest in one or two days. Among mammals, most ungulates are precocial, being able to walk almost immediately after birth.

Etymology<br>[edit]

The word "precocial" is derived from the Latin root praecox, the same root as in precocious, meaning early maturity.[2]

Superprecociality<br>[edit]

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.[3] Enantiornithes[4] and pterosaurs[citation needed] 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;[5][6] they can outrun a hyena within a day.[7][8][9] Such behavior gives them an advantage over other herbivore species and 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. They are unable to keep up with their mothers until they are more than a week old.[9]

Black mambas are highly precocial; as hatchlings, they are fully independent, and are capable of hunting prey the size of a small rat.[10]

Phylogeny<br>[edit]

Precociality is thought to be ancestral in birds. Thus, altricial birds tend to be found in the most derived groups. There is some evidence for precociality in protobirds[11] and troodontids.[12] Enantiornithes at least were superprecocial in a way similar to that of megapodes, being able to fly soon after birth.[4] It has been speculated that superprecociality prevented enantiornithines from acquiring specialized toe anatomy seen in modern altricial birds.[13]

Altriciality<br>[edit]

A human infant<br>In birds and mammals, altricial species are those whose newly hatched or 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 length of time. Altricial birds include hawks, herons, woodpeckers, owls, cuckoos and most passerines. Among mammals, marsupials and most rodents are altricial. Domestic cats, dogs, and primates, such as humans, are some of the best-known altricial organisms.[14] For example, newborn domestic cats cannot see, hear, maintain their own body temperature, or gag, and require external stimulation in order to defecate and urinate.[15] The giant panda is notably the largest placental mammal to have altricial, hairless young upon birth. The larval stage of insect development is considered by some to be a form of altricial development, but it more accurately depicts, especially amongst eusocial animals, an independent phase of development, as the larvae of bees, ants, and many arachnids are completely physically different from their developed forms, and the pre-pupal stages of insect life might be regarded as equivalent to vertebrate embryonic development.

Etymology<br>[edit]

The word "altriciality" is derived from the Latin root alere, meaning "to nurse, to rear, or to nourish", and...