Precocity


In biology, the term precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called "altricial" where the young are born or hatched helpless. Extremely precocial species may be called "superprecocial". These three categories form a continuum, without distinct gaps between them. Precocial species are normally nidifugous, meaning that they leave the nest shortly after birth or hatching.

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.[1] These kind of birds can also swim and run much sooner after their birth than other birds, such as songbirds.[1] 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 the megapodes, where the newly-hatched chicks dig themselves out of the nest mound without parental assistance, and fly on the first day after hatching.

Precociality is found in many other animal 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 phenomenon of imprinting studied by Konrad Lorenz is characteristic of precocial birds.

Etymology

The word "precocial" is derived from the same root as precocious, implying in both cases early maturity.[2]

Phylogeny

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 (Elzanowski, 1995.) and Troodontids (Varricchio et al. 2002).

See also

References

Footnotes

Notations

  • Starck J.M., Ricklefs R. E. Patterns of Development: The Altricial - Precocial Spectrum. In; Avian Growth and Development. Oxford University Press, New York, NY, 1998.
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