Impact of time since collection on avian eggshell color: a comparison of museum and fresh egg specimens |
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Authors: | Phillip Cassey Golo Maurer Camille Duval John G Ewen Mark E Hauber |
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Institution: | (1) Centre for Ornithology, School of Biosciences, Birmingham University, Edgbaston, B15 2TT, UK;(2) Institute of Zoology, Regents Park, London, UK;(3) Department of Psychology, Hunter College of the City University of New York, New York, NY, USA |
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Abstract: | Studies of avian eggshell coloration have been a long-standing research focus in behavioral evolutionary ecology. Museum collections
have provided a widely used resource because they allow efficient sampling across broad temporal, geographical, and taxonomic
ranges, even for species that are rare and for which sampling in the wild is ethically or practically unwarranted. We used
reflectance spectrophotometry across the avian visual spectrum to compare eggshell color of specimens of the song thrush (Turdus philomelos) in two museums (Natural History Museum, UK and Auckland Museum, New Zealand) with each other and with eggshells collected
fresh in New Zealand. These data enabled us to test the effects of source and storage in different museums, as well as time
since collection, across four metrics of eggshell coloration: blue-green and ultraviolet chroma, overall brightness, and the
spectral coefficient of variation. Variation within an egg, within a clutch, and among clutches, was similar between the two
museum datasets but different from those of fresh eggs. We found significant differences in all four metrics between the collections,
and that fresh eggshells reflected stronger in the blue-green wavelength than in museum eggs. This difference is most likely
due to different preservation techniques and storage histories. Furthermore, an effect of time since collection was only apparent
in the blue-green chroma and was higher in more recent museum eggshell samples. Our results support the use of historic museum
samples in intraspecific studies of shell coloration providing that efforts are made to compare specimens, which were collected
during similar periods. |
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