Preservation agents influence UV-coloration of plumage in museum bird skins

Plumage colour has always been a major criterion when describing and distinguishing bird taxa. Today, the use of reflection spectrophotometry is the most commonly used technique to study plumage coloration. A major advantage of this method is the opportunity of observing reflection beyond the human colour vision range-including the UV-waveband. Traditional taxonomic and phylogenetic research is often based on bird skins held in collections in natural history museums worldwide. Different agents for preservation have been used to prevent skins from being damaged by arthropod pests. Sometimes, parts of the plumage have been contaminated with stains from preservation agents. When dried, they are almost invisible to the human eye under normal sunlight conditions and cause no obvious change to feather coloration. However, some preservation agents contain fluorescent components which show up brightly when illuminated with UV-light. Furthermore, undetectable to the human eye, stains from these agents annihilate UV-reflection, preventing accurate data collection based on the UV-reflection of bird feathers. Measuring plumage parts which have been accidentally stained will lead to a relative underestimate of UV-reflection. In studying 20,000 samples, we found fluorescent stains in some 300 bird skins of varying ages (1913-2004) in museum collections throughout Europe and the USA. Different preservation agents have been evaluated for their fluorescence properties.