McNett, G.D., & Marchetti, K. (2005). Ultraviolet degradation in carotenoid patches: Live versus museum specimens of wood warblers (Parulidae). The Auk, 122(3): 793-802.

In this investigation, the authors demonstrated that museum specimens of wood-warblers may not be representative of natural color in live specimens, especially in terms of ultraviolet reflectance. Plumage coloration was measured in ten species of warblers. Live males were captured in mist nets in New York, and museum specimens came from the American Museum of Natural History in New York. Plumage color spectra were measured using an S2000 Spectrometer with OOIBASE10 data-acquisition software and a light source attached to a bifurcated optical fiber with reflectance measuring probe. Measurements were obtained for brightness, chroma and hue.

Mean brightness, chroma and hue of carotenoid patches differed significantly between live and museum specimens. In addition, there was a discrepancy between the degradation of UV reflectance and human visible spectrum reflectance. This result suggests that UV reflectance degrades more rapidly in museum specimens than other wavelengths. These results highlight the importance of using live specimens when investigating anything affected by plumage color.

This paper pertains to our lecture on production and transmission of light signals. The authors describe the carotenoid pigments found in warbler plumage, and how these carotenoid pigments produce a UV peak by minimally absorbing wavelengths in the UV range. Our lecture described how surfaces can appear colored by reflecting certain wavelengths and absorbing others. In class we also talked about pigments that transmit certain wavelengths, and how carotenoids appear yellow, orange or red.

The authors also described the properties of light signals they measured, which are described in our lecture and textbook. They measured brightness, hue and chroma of the warbler plumage.

One good point that is raised in our textbook is that all of the strategies that we believe are used for maximizing contrast are based on human perception. This paper highlights the need to consider the sensation and perception capabilities of animals other than humans when studying animal communication. We as humans may study museum specimens and infer that because they look like live specimens to us, they would look normal to other birds.

The authors also point out that while the spectral sensitivity of photoreceptors in warblers has not been reported, all passerines previously studied have photoreceptors that correspond to UV-violet, blue, green, and red wavelengths. Therefore, these animals probably classify color differently than we do. Our lecture on light signal reception goes into more detail on how birds generate visual pigments with different absorption peaks using colored oil droplets that can narrow the spectral absorption curves.