When an animal is altricial, it means that it is born in a helpless state, reliant on its parents for support and protection until it matures. This is in opposition to a precocial animal, an animal which is capable of moving around on its own shortly after birth. Many species of birds are famously altricial, being born naked, blind, and totally helpless, while animals like ungulates tend to be precocial. Altricial animals develop differently from precocial animals, displaying markedly different traits later in life as well as in childhood.
As a general rule, altricial animals are born to parents who might have difficulty defending themselves in the late stages of pregnancy or nesting, making it imperative for the young to be born as quickly as possible. The mothers may also be incapable of providing needed nutrition to the young while they develop. In the case of birds, for example, the mother bird may not be able to build enough egg yolk for the young to develop more fully in the egg.
When an altricial animal is born, it is often blind, and it may lack the plumage or fur associated with adults of the species. Altricial animals also tend to be helpless, unable to move around like mature adults and dependent on others for support, food, shelter, and companionship. Many marsupials, for example, are born naked or blind; baby kangaroos are perhaps one of the more outstanding examples of an altricial animal, as they are born in a form which borders on embryonic. Humans are also altricial, with an extremely long period of development required before they reach maturity.
The parents must therefore have a protected area for their young, and may also have to actively work to protect the babies. Mother rats, for example, are quite ferocious when threatened, and songbirds may use a variety of tricks to distract predators in the hopes of saving their nestlings. One big advantage to being born in altricial state is that the animal's brain will continue to develop and grow for years after birth, allowing altricial animals to learn more and develop wider skill sets than their precocial counterparts.
There are various degrees along the scale when it comes to being born altricial. While some animals demonstrate extreme degrees of altricial or precocious traits, most fall somewhere in the middle. For example, chicks and ducklings are capable of moving around within a few hours of hatching, and they are born with their eyes open, but they are clearly dependent on their parents for warmth and shelter.