underparts

Underparts are the ventral surfaces of an animal's body, including the chest, abdomen, and often the flanks and undertail region. In birds and mammals the term is commonly used to describe the coloration and pattern on the underside compared with the upperparts (dorsal surface). In fish and reptiles, ventral coloration similarly refers to the underside.

Functions and variation: Underparts coloration can serve camouflage through countershading, where a darker back and lighter belly reduces silhouette when viewed from above or below. In many birds, underparts are a key field mark: for example, a white or pale throat or breast may contrast with darker upperparts and aid species recognition by observers or signal quality during breeding. In some species, underparts are brightly colored to attract mates or deter rivals.

Description and identification: Field guides describe underparts separately as throat, chest, belly, flanks, undertail coverts, and vent. The precise colors or patterns are used to differentiate species or subspecies; changes in season may occur in plumage, molt, or breeding conditions.

Examples: Penguins typically have dark backs and white or pale underparts. Many passerines exhibit pale chests and bellies, while some shorebirds show rufous or spotted underparts. In mammals, ventral fur color may be lighter than dorsal fur, providing camouflage.

Other uses: In clothing or textiles, underparts can refer to inner garments or linings worn beneath outer clothing; however, this usage is separate from the biological sense.