Terminology
In birds, the terms Aves altrices and Aves precoces was introduced by Carl Jakob Sundevall (1836) and the terms nidifugous and nidicolous by Lorenz Oken in 1816. The two classifications were considered identical in early times, but the meanings are slightly different, in that "altricial" and "precocial" refer to developmental stage, while "nidifugous" and "nidicolous" refer to leaving or staying at the nest.
The two strategies result in different brain sizes of the newborns compared to adults. Precocial animals' brains are large at birth relative to their body size, hence their ability to fend for themselves. However, as adults, their brains are not much bigger or more able. Altricial animals' brains are relatively small at birth, thus their need for care and protection, but their brains continue to grow. As adults, altricial animals end up with comparatively larger brains than their precocial counterparts. Thus the altricial species have a wider skill set at maturity.
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