Thus the altricial species have a wider skill set at maturity.

The span between precocial and altricial species is particularly broad in birds.

Altricial species are relatively helpless at birth and require considerable parental care and protection.

The northern grasshopper mouse is an altricial species; baby mice are naked with closed eyes when they are born, and weigh about three grams.

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.

In bird and mammal biology, altricial species are those whose newly-hatched or -born young are relatively immobile, lack hair or down, not able to obtain food on their own, and must be cared for by adults; closed eyes are common, though not ubiquitous.