Animals are often conspicuously colored and explanations range from aposematism and mimicry to sexual selection. Although sexual selection explains vivid coloration in males, functional significance of vivid coloration in females of socially monogamous species remains unclear. The hypothesis of mutual mate choice predicts that more ornamented females produce offspring of higher quality. We tested this prediction in the great tit (Parus major), a small, insectivorous, socially monogamous passerine.
Remeš, V., & Matysioková, B. (2013). More ornamented females produce higher-quality offspring in a socially monogamous bird: An experimental study in the great tit (Parus major). Frontiers in Zoology, 10(1). https://doi.org/10.1186/1742-9994-10-14