Taste is crucial in shaping animal perception. Sourness, one of the primary tastes, is aversive in mammals, whereas many birds frequently consume acidic fruits, suggesting a potential tolerance. Our study uncovers a mechanism enabling avian sour tolerance that involves changes to the sour receptor [otopetrin 1 (OTOP1)]. We demonstrate that sour tolerance is a conserved trait in birds, with avian OTOP1 exhibiting acid-induced inhibition and OTOP1 modulation affecting sour perception and tolerance. Ancestral reconstruction reveals that the increase in acid tolerance may have evolved at the same point in the songbird phylogeny as the regain of sweet sensing in this clade. This shift might have enabled songbirds to feed on a wider range of fruits, affecting the evolution and diversification of the songbird radiation.