An Examination of Male and Female Gray Catbird (Dumetella carolinensis) Feather Reflectance in the Visible and Ultraviolet spectrum

Sexual dichromatism is the difference in coloration between males and females of the same species that is caused by the inheritance of genetic material. Bird feathers are composed of various pigments which contribute to sexual dichromatism. The most abundant and widespread feather pigment, melanin, contributes to this diversity. Recently, it has been discovered that current categorizations of avian dichromatism may be incorrect with the discovery that some bird species can see in the ultraviolet (UV) light region, which humans cannot see. Therefore, the former categorizations of sexual dichromatism for bird feathers based on human visual assessment may be incorrect. In this study, I used an Ocean Optics USB4000 spectrometer to evaluate reflectance characteristics in gray catbird (Dumetella carolinensis) rectrix feathers. This species was chosen because it has been previously categorized as sexually monochromatic. My objectives were threefold. First, I sought to determine if male and females were different in any of three color variables: brightness, hue, and saturation. Second, I sought to determine if male and female feathers were reflecting in the UV region. Third, I sought to determine if there were any differences in UV reflectance between males and females in the UV region. I found that females were brighter and had higher hue values than males, but found no difference in saturation. I also found evidence of UV reflectance for both male and female catbirds and that females reflected more in the UV region than males. While it is possible that these differences are due to sexual selection, my results suggest that they may instead be a result of ecological differences that occur between the sexes or that they might be a side effect of hormonal differences between the sexes during the molting period