The Chestnut-sided Warbler is a medium-sized warbler with distinct chestnut-colored flanks, a yellow cap, and black eye streaks. The males' colors are bright and vibrant, while the female resembles a washed-out version of the male. During mating season, male chestnut-sided warblers sing an accented "pleased, pleased, pleased to MEETCHA" song to attract females. This same song, without the accent on the last syllable, is used to defend their territories once nesting is underway. The Chestnut-sided Warbler prefers to spend three seasons in second-growth habitats, and winters in the mature tropical rainforests of Central America. It feeds mostly on insects, picking them off the undersides of leaves or attempting to catch them in mid-air.