Microclimate of nesting burrows of the Rainbow Bee-eater
Alan Lill A B C and Peter J. Fell AA Wildlife Ecology Research Group, School of Biological Sciences, Monash University, Clayton Campus, Vic. 3800, Australia.
B School of Psychology, Psychiatry and Psychological Medicine, Monash University, Clayton Campus, Vic. 3800, Australia.
C Corresponding author. Email: Alan.Lill@sci.monash.edu.au
Emu 107(2) 108-114 https://doi.org/10.1071/MU06046
Submitted: 11 December 2006 Accepted: 8 May 2007 Published: 13 June 2007
Abstract
Burrow-nesting affords protection from predators and climatic extremes, but potentially can pose physiological ‘problems’ for developing birds and attendant adults. Microclimate parameters of burrows of breeding Rainbow Bee-eaters (Merops ornatus) were measured to assess whether they presented such difficulties for young and adults. Estimated mean volume of the brood-chamber was ~4.5 L. Relative humidity was typically 100% in the brood-chamber and chamber air temperature was constant, averaging 4–6°C above ambient levels. The temperature regime of the burrow probably resulted in low thermoregulatory costs for attendant adults and endothermic nestlings. The chamber oxygen (O2) fraction (mean 19.35%) was always lower than ambient values, but mostly not sufficiently low to be problematic for the growing young. Mean pre-internal pipping absolute oxygen consumption rate of embryos (62.9 ± 13.8 mL O2 day–1) did not appear to be strongly influenced by either the protracted incubation period or the reduced O2 partial pressure of the chamber atmosphere. Mean eggshell water-vapour conductance (8.95 mg day–1 kPa–1) was tuned to egg mass rather than egg mass/incubation period. However, eggs still lost ~15% of their mass during incubation because the influence of the small water-vapour pressure difference across the shell (2.91 kPa) and the protraction of the incubation period apparently counteracted each other.
Acknowledgements
We gratefully acknowledge the assistance of George and (the late) Dorothy Merritt, David and Thelma Basselot-Hall, Bob Wood, Frank Devlin, the Victorian Department of Sustainability and Environment, Peter Domelow and Max Hart. Approval for the investigation was obtained from the Monash University School of Biological Sciences Animal Ethics Committee. Three anonymous referees provided some useful comments on the manuscript.
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