Museum collections have great value for zoological research, but despite careful preservation, over time specimens can show subtle changes in color. We examined the effect of storage time on fur color of two reddish-brown species, golden mice (Ochrotomys nuttalli) and eastern chipmunk (Tamias striatus). Using image analysis, we obtained color data (hue, saturation, and density) on 91 golden mice and 49 chipmunks from Georgia, USA. Analyses that considered body size, gender, and collection year showed significant effects of year on fur color of golden mice (hue and saturation) and of agouti color of chipmunks. Older specimens tended to be redder in color than newer specimens, consistent with a prior study of red bats (Lasiurus borealis). Hair samples showed reddening of fine body hairs, but not in thicker guard hairs. There was no temporal change in black or white stripe color in chipmunks, indicating that this temporal effect would be limited to species with reddish-brown fur. This effect may be caused by breakdown of eumelanin pigments (which make dark colors) over time, leaving a greater proportion of pheomelanin pigments (which make red colors). These results show that storage time needs to be considered in research projects where fur color is of importance. 1. Introduction Museum collections of animals have always been a valuable resource for zoological research. Older specimens in particular offer insights into the past and allow researchers to track the historical incidence of deformities [1], document species declines [2], and extract DNA for genetic analyses [3]. An implicit assumption with all museum collections is that once a specimen is added to a collection and properly stored, it remains unchanged through time. In a recent museum study of pelage color in red bats (Lasiurus borealis), a curious discovery was made, where older specimens tended to have redder shades of pelage than did newer specimens [4], which is the opposite patter one would expect if specimens simply faded over time. Indeed, color fading does happen when specimens (of most taxa) are exposed to light [5, 6] such as in museum exhibits. However, these bat specimens had always been housed in drawers within standard metal museum cabinets (i.e., in darkness). At the time, it was thought that this was from breakage of buffy-tipped hair fibres on older specimens. Since that study, we have examined two additional mammal species in this same museum to look for evidence of temporal color changes in their fur, and we report the results of these investigations here. Aside from the
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