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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.

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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 iD for 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 Creative Commons Attribution licence
Persistent URL http://hdl.handle.net/10536/DRO/DU:30090814

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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.