title: Thermal emissivity of avian eggshells.
abstract: The hypothesis has been tested that evolution has resulted in lower thermal emissivity of eggs of birds breeding openly in cold climates than of eggs of birds that nest under protective covering or in warmer climates. Directional thermal emissivity has been estimated from directional-hemispherical reflectance spectra. Due to several methodological difficulties the absolute emissivity is not accurately determined, but differences between species are obvious. Most notably, small waders of the genus Calidris, breeding in cold climates on the tundra, and in most cases with uniparental nest attendance, have low directional emissivity of their eggshells, about 0.92 when integration is carried out for wavelengths up to 16μm. Species belonging to Galloanserinae have the highest directional emissivity, about 0.96, of their eggs. No differences due to climate or breeding conditions were found within this group. Eggs of most other birds tested possess intermediate emissivity, but the values for Pica pica and Corvus corone cornix are as low as for Calidris. Large species-dependent differences in spectral reflectance were found at specific wavelengths. For instance, at 4.259μm the directional-hemispherical reflectance for galliforms range from 0.05 to 0.09, while for Fratercula arctica and Fulmarus glacialis it is about 0.3. The reflection peaks at 6.5 and 11.3μm due to calcite are differentially attenuated in different species. In conclusion, the hypothesis that evolution has resulted in lower thermal emissivity of bird eggs being exposed in cold climates is not supported by our results. The emissivity is not clearly related to nesting habits or climate, and it is unlikely that the small differences observed are ecologically important. The spectral differences between eggs that nevertheless exist should be taken into account when using infrared thermometers for estimating the surface temperature of avian eggs.
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, School of Life Science, South China Normal University, Guangzhou 510631, China; Lund University, Department of Biology, Sölvegatan 35, SE-22362 Lund, Sweden. Electronic address: Lars_Olof_Bjorn@biol.lu.se.
authors.forename: Lars Olof
authors.initials: LO
authors.lastname: Björn
authors.affiliation: Lund University, Department of Biology, Sölvegatan 35, SE-22362 Lund, Sweden.
authors.forename: Sven-Axel
authors.initials: SA
authors.lastname: Bengtson
authors.affiliation: Key Laboratory of Ecology and Environmental Science in Guangdong Higher Education, School of Life Science, South China Normal University, Guangzhou 510631, China. Electronic address: lishsh@scnu.edu.cn.
authors.forename: Shaoshan
authors.initials: S
authors.lastname: Li
authors.affiliation: University of Twente, Faculty of Geo-Information Science and Earth Observation (ITC), Department of Earth Systems Analysis, 7500AA Enschede, The Netherlands.
authors.forename: Christoph
authors.initials: C
authors.lastname: Hecker
authors.affiliation: Department of Space Sciences, Institute of Space Technology, P.O. Box 2750, Islamabad, Pakistan.
authors.forename: Saleem
authors.initials: S
authors.lastname: Ullah
authors.affiliation: Uppsala University, Dept of Engineering Sciences, Solid State Physics, Box 534, 751 21 Uppsala, Sweden.
authors.forename: Arne
authors.initials: A
authors.lastname: Roos
authors.affiliation: Uppsala University, Dept of Engineering Sciences, Solid State Physics, Box 534, 751 21 Uppsala, Sweden.
authors.forename: Annica M
authors.initials: AM
authors.lastname: Nilsson
mesh_terms: D000064:Acclimatization; D000818:Animals; D005075:Biological Evolution; D001833:Body Temperature Regulation; D046091:Charadriiformes / Q000235:genetics* / Q000502:physiology; D004528:Egg Shell / Q000502:physiology*; D007259:Infrared Rays; D013696:Temperature
keywords: Avian eggs; Birds; Egg cooling; Heat dissipation; Incubation; Seabirds; Thermal emissivity; Thermal radiation; Waders