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A nidicolous animal (from Latin: nidus "nest" and colous "inhabiting") is an animal that appears undeveloped at birth and stays at their birthplace for a long time, due to their dependence on the parents for feeding, protection and learning survival skills. They are the opposite of nidifugous species who leave their parents more quickly and survive independently. Another pair of terms to describe this developmental phenomenon, altricial and precocial, is also used by scientists.
Examples of nidicolous species are most mammals, marsupials and many species of birds. The great majority of nidicolous animals are altricial; an animal born helpless, blind and without feathers or hair, simply unable to fend for itself. During the life span, the brain of a nidicolous animal expands 8–10 times of its initial size; in nidifugous animals, from 1.5 to 2.5 times. Humans are precocial-born, nonetheless their brains, which at birth constitute 25% of their adult size, continue to expand significantly during lifetime. However, the concepts of altricial and nidicolous are not identical. All altricial animals are nidicolous by necessity, but an animal may be nidicolous, such as staying at the nest, even if it is precocial and fully capable of leaving if needed.