Spatial variation in avian bill size is associated with humidity in summer among Australian passerines Gardner, Janet L., Symonds, Matthew R.E., Joseph, Leo, Ikin, Karen, Stein, John and Kruuk, Loeske E.B. 2016, Spatial variation in avian bill size is associated with humidity in summer among Australian passerines, Climate change responses, vol. 3, pp. 1-11, doi: 10.1186/s40665-016-0026-z. Attached Files Name Description MIMEType Size Downloads symonds-spatialvariation-2016.pdf Published version application/pdf 842.54KB 12 Title Spatial variation in avian bill size is associated with humidity in summer among Australian passerines Author(s) Gardner, Janet L. Symonds, Matthew R.E. orcid.org/0000-0002-9785-6045 Joseph, Leo Ikin, Karen Stein, John Kruuk, Loeske E.B. Journal name Climate change responses Volume number 3 Article ID 11 Start page 1 End page 11 Total pages 11 Publisher BioMed Central Place of publication London, Eng. Publication date 2016-12 ISSN 2053-7565 2053-7565 Keyword(s) Meliphagoidea Honeyeaters, Thermoregulation, Bill morphology, Summary Background: Climate imposes multiple selection pressures on animal morphology. Allen’s Rule proposes thatgeographic variation in the appendage size of endotherms, relative to body size, is linked to climatic variation,thereby facilitating heat exchange and body temperature regulation. Thus relatively larger appendages tend to befound in animals in warmer climates. Despite growing understanding of the role of the avian bill as an organ forheat exchange, few studies have tested the ecological significance of bill size for heat dissipation across speciesand environmental gradients. Amongst those that have, most have focused on the relationship with ambienttemperature, but there is growing evidence that humidity also has a strong influence on heat dissipation. Inparticular, increasing humidity reduces the potential for evaporative cooling, favouring radiative and convectiveheat loss via the bill, and hence potentially favouring larger bills in humid environments. Here, we usedphylogenetically-controlled analyses of the bill morphology of 36 species of Australian passerines to explore therelationship between bill size and multiple aspects of climate. Results: Humidity during the hot summer months (December-February) was positively associated with relative billsurface area across species. There was no overall association between bill size and summer temperatures per se, butthe association with humidity was mediated by temperature, with a significant interaction indicating strongerassociations with humidity at cooler summer temperatures. This is consistent with the idea that larger bills maybecome disadvantageous in humid conditions as ambient temperature approaches body temperature. Relative billsize was similar among closely related species, with phylogeny explaining 63.3% of the variance, and there wassignificant variation among species in their response to humidity. However, the relationship between relative billsize and humidity was not associated with phylogeny. Conclusions: Our results are consistent with the idea that body temperature regulation underlies continent-widepatterns of bill size variation in a broad range of Australian passerines, and suggests that Allen’s Rule may apply tohumidity gradients as well as temperature gradients. They add to growing evidence that a narrow focus ontemperature alone in studies of responses to climate change may limit our understanding of species’ sensitivities toclimatic variation, and of their capacity to adapt. Language eng DOI 10.1186/s40665-016-0026-z Field of Research 060303 Biological Adaptation Socio Economic Objective 970106 Expanding Knowledge in the Biological Sciences HERDC Research category C1 Refereed article in a scholarly journal ERA Research output type C Journal article Copyright notice ©2016, The Authors Free to Read? Yes Use Rights Persistent URL http://hdl.handle.net/10536/DRO/DU:30090814 Document type: Journal Article Collections: School of Life and Environmental Sciences Open Access Collection Centre for Integrative Ecology Related Links Link Description Connect to published version Go to link with your DU access privileges     Unless expressly stated otherwise, the copyright for items in DRO is owned by the author, with all rights reserved. Every reasonable effort has been made to ensure that permission has been obtained for items included in DRO. If you believe that your rights have been infringed by this repository, please contact drosupport@deakin.edu.au. 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