Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the fetus at a developmental stage when it is ready to feed and breathe.
Lambing: the mother licks the first lamb while giving birth to the second
An illustration of normal head-first presentation by the obstetrician William Smellie from about 1792. The membranes have ruptured and the cervix is fully dilated.
A cow giving birth
A kangaroo joey firmly attached to a nipple inside the pouch
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. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. These categories form a continuum, without distinct gaps between them.
Altricial young birds
California quail chick (Callipepla californica), a precocial chick
A human baby. Humans are among the best-known altricial organisms.
