heat loss may explain bill size differences between birds occupying different habitats热损失可以解释比尔占据不同的鸟类栖息地之间的大小差异.pdfVIP

Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats 1 2 1,3 2 Russell Greenberg *, Viviana Cadena , Raymond M. Danner , Glenn Tattersall 1 Smithsonian Migratory Bird Center, Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC, United States of America, 2 Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada, 3 Avian Ecology Group, Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States of America Abstract Background: Research on variation in bill morphology has focused on the role of diet. Bills have other functions, however, including a role in heat and water balance. The role of the bill in heat loss may be particularly important in birds where water is limiting. Song sparrows localized in coastal dunes and salt marsh edge (Melospiza melodia atlantica) are similar in size to, but have bills with a 17% greater surface area than, those that live in mesic habitats (M. m. melodia), a pattern shared with other coastal sparrows. We tested the hypotheses that sparrows can use their bills to dissipate ‘‘dry’’ heat, and that heat loss from the bill is higher in M. m. atlantica than M. m. melodia, which would indicate a role of heat loss and water conservation in selection for bill size. Methodology/Principal Findings: Bill, tarsus, and body surface temperatures were measured using thermal imaging of sparrows exposed to temperatures from 15–37uC and combined with surface area and physical modeling to estimate the contribution of each body part to total heat loss. Song sparrow bills averaged 5–10uC hotter than ambient. The bill of M. m atlantica dissipated up to