ABSTRACT
Many juvenile birds turn into long-distance migrants within weeks of fledging. This transition involves upheavals in their energy management as major changes in growth and activity occur. Understanding such ontogenetic transitions in energy allocation has been difficult because collecting continuous data on energy costs in wild developing birds was previously largely impossible. Here, we continuously measured heart rate and fine-scale movements of 20 free-living juvenile white storks (Ciconia ciconia) using on-board bio-loggers to explore individual and environmental factors relating to daily mean heart rate. In addition, we explored which specific energy management strategy storks use during these crucial early life stages. We found that daily mean heart rate increased with overall movement activity, and increasing body temperature, but that it decreased with age. Further, we found that during the nestling period, when growth costs are high, activity costs are low, and post-fledging that activity costs are increased while maintenance costs are low, indicating a constraint on overall energy use in both phases. Our observations are consistent with the hypothesis that individuals invested more energy per unit time while still in the nest than after fledging despite the high costs of flight.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: A.F., W.F.; Methodology: I.M.; Formal analysis: A.F.; Data curation: P.J.S.; Writing - original draft: A.F.; Writing - review & editing: A.F., P.J.S.; Project administration: J.R.E.T., W.F.; Funding acquisition: J.R.E.T., M.W., W.F.
Funding
We acknowledge funding from the Max Planck Institute for Ornithology and the Max Planck-Poland Biodiversity Initiative. A.F. was supported by Deutsches Zentrum für Luft- und Raumfahrt and Christiane Nüsslein-Volhard Stiftung.
Supplementary information
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.219337.supplemental
- Received November 26, 2019.
- Accepted December 17, 2019.
- © 2020. Published by The Company of Biologists Ltd
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