Plant-eating mammals abound in the trees of the deciduous forests, eating shoots and leaf buds in the spring and fruits and nuts in the autumn. The chirit is a typical plant-eating mammal. Its peculiar shape is a legacy from an immediate ancestor, the chiselhead of the northern coniferous forests. As it spread south into the temperate woodlands it found that it no longer needed to make deep tunnels in the trees to escape the harsh winter, and as a result the animal's specialized chiseling and gnawing teeth became smaller, its dentition reverting to be more like that of its distant ancestor the eastern grey squirrel. Its bodily shape, however, was still perfectly adapted to life in the trees and remained unchanged.