This species is a moderately-sized New World warbler. Despite having very different plumage, it is thought to be closely related to the widespread yellow warbler. In total, this species measures from 10 to 14 cm (3.9 to 5.5 in) in length and spans 16 to 21 cm (6.3 to 8.3 in) across the wings. Body weight ranges from 8 to 13.1 g (0.28 to 0.46 oz). Among standard measurements, the wing chord is 5.7 to 6.8 cm (2.2 to 2.7 in), the tail is 4.2 to 5.8 cm (1.7 to 2.3 in), the bill is 0.9 to 1 cm (0.35 to 0.39 in) and the tarsus is 1.7 to 1.9 cm (0.67 to 0.75 in). In the summer, male chestnut-sided warblers are unmistakable in appearance. They display dark-streaked gray backs, white faces, black eyestripes and greenish crowns. Their underparts are white, with chestnut flanks, and they also have two white wing bars. The adult females resemble washed-out versions of the summer male, and in particular, the females lack the strong head pattern, and also have little to no chestnut coloring on their flanks. Non-breeding birds of both sexes have greenish heads, and greenish upperparts which are usually unstreaked. They also have unstreaked pale grey breasts. Their wing bars are always present in their plumages. Their lack of streaking and greenish backs helps to distinguish this species from the larger blackpoll warbler in the fall. Learn more about Chestnut-Sided Warbler