The finches, which are considered the most highly developed of the birds, are widely diversified; they are classified into three groups: those with small, triangular bills, such as the canary, sparrow, bunting, towhee, junco, and those birds specifically named finch (e.g., chaffinch, bullfinch, and goldfinch); those with thick, rounded bills, as the grosbeak and cardinal; and the crossbills, rose-colored northern birds whose mandibles, as their name implies, cross over at the tips—an adaptation suited to their diet of conifer seeds.
The sparrows, genus Passer, which are field and hedge birds, are inconspicuously colored in dull grays and browns, but among the other, tree-perching finches, the male is often brightly plumaged (although the female is usually duller and sparrowlike). Most finches (except the meticulous goldfinch) build sloppy cup-shaped nests for their four to six speckled eggs.
Other species commonly called finches, especially many species kept as pets, are also found in other bird families. Estrildidae includes the grass, zebra, and parrot finches, waxbills, and munias, and Ploceidae includes the weaverbirds and whydahs.