One of many examples of indicator traits is the condition-dependent patch of red feathers around the face and shoulders of the male house finch. This patch varies in brightness among individuals because the pigments that produce the red color (carotenoids) are limited in the environment. Thus, males who have a high-quality diet will have brighter red plumage. In a manipulation experiment, female house finches were shown to prefer males with brighter red patches. Also, males with naturally brighter patches proved better fathers and exhibited higher offspring-feeding rates than duller males. This study is heavily cited in the literature and it provides solid support for the indicator-traits hypothesis that is associated with direct benefits.