Moult-related reduction of aerobic scope in passerine birds
It is well established that the nutrient and energy requirements of birds increase substantially during moult, but it is not known if these increased demands affect their aerobic capacity. We quantified the absolute aerobic scope of house and Spanish sparrows, Passer domesticus and P. hispaniolensis, respectively, before and during sequential stages of their moult period. The absolute aerobic scope (AAS) is the difference between maximum metabolic rate (MMR) during peak locomotor activities and minimum resting metabolic rate (RMRmin), thus representing the amount of aerobic power above that committed to maintenance needs available for other activities. As expected, RMRmin increased over the moult period by up to 40 and 63% in house and Spanish sparrows, respectively. Surprisingly, the maximum metabolic rates also decreased during moult in both species, declining as much as 25 and 38% compared with pre-moult values of house and Spanish sparrows, respectively. The concurrent changes in RMRmin and MMR during moult resulted in significant decreases in AAS, being up to 32 and 47% lower than pre-moult levels of house and Spanish sparrows, respectively, during moult stages having substantial feather replacement. We argue that the combination of reduced flight efficiency due to loss of wing feathers and reduced aerobic capacity places moulting birds at greater risk of predation. Such performance constraints likely contribute to most birds temporally separating moult from annual events requiring peak physiological capacity such as breeding and migration.
KeywordsAvian moult energetics Aerobic scope Resting metabolic rate Maximum metabolic rate Passer domesticus Passer hispaniolensis
We thank Pavel Zehtindjiev for facilitating our research at Kalimok Station and Martin Marinov, Katrina Ivanova, and Mihaela Ilieva for animal care assistance, and the four anonymous reviewers for their constructive comments. All experimental procedures were carried out under the permission and guidelines of the Bulgarian Academy of Sciences and the Bulgarian Ministry of Environment and Waters (no. 627/30.03.2015). All birds were released at the end of study. This study is report No. 65 of the Biological Experimental Station ‘Kalimok’.
SH, SB and WAB developed the conceptual framework and analysed the data. SH, TE and WAB made metabolic measurements. SH, SB and WAB wrote the manuscript. DD, SP, SH, TE and WAB captured birds and made morphological measurements.
This study was supported by the Swiss National Science Foundation (31003A_160265) to S.B. and S.H.
Compliance with ethical standards
Conflict of interest
All authors discussed and approved the manuscript and have no competing interests.
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