Dual functions of a melanin-based ornamentin the common yellowthroat

Melanin-based ornaments often function as signals in male-male competition, whereas carotenoid-based ornaments appear to be important in female mate choice. This difference in function is thought to occur because carotenoid pigments are more costly to produce than melanins and are thus more reliable indicators of male quality.

Scott A. Tarof et al., Proc. R. Soc. B (2005) 272, 1121-1127