https://phaidra.vetmeduni.ac.at/o:2769 Empirical Evidence for Energy Efficiency Using Intermittent Gliding Flight in Northern Bald Ibises Mizrahy-Rewald, Ortal Ortal Mizrahy-Rewald Waldrappteam Conservation & Research Ruf, Thomas Thomas Ruf 0000-0002-9235-7079 University of Veterinary Medicine Vienna Voelkl, Bernhard Bernhard Voelkl University of Bern Fusani, Leonida Leonida Fusani 0000-0001-8900-796X University of Veterinary Medicine Vienna / University of Vienna, Vyssotski, Alexei L. Alexei L. Vyssotski ETH Zurich Perinot, Elisa Elisa Perinot 0000-0003-0379-8508 University of Veterinary Medicine Vienna / Waldrappteam Conservation & Research Fritz, Johannes Johannes Fritz Waldrappteam Conservation & Research Frontiers Media Sa text eng Birds face exceptionally high energy demands during their flight. One visible feature of some species is alternating between flapping and gliding, which should allow them to save energy. To date, there is no empirical evidence of an energetic benefit to this. To understand the physiology behind the strategy, we equipped hand-raised Northern Bald Ibises (Geronticus eremita) with data loggers during human-guided migration. We monitored the position of the birds, wingbeats, overall dynamic body acceleration (ODBA), and heart rates as a proxy for energy expenditure. The energy expenditure was significantly affected by the length of flapping and gliding bouts. A pronounced decrease in heart rate was measured after already 1 s of gliding. Additionally, the heart rate at flapping bouts up to 30 s increased steadily but stabilized thereafter. The gilding proportion during intermittent flight affected the energy saving compared to continuous flapping. At a gliding proportion of about 20%, we measured a maximum of 11% saving based on heart rate measurement. At higher gliding proportions, the additional energy saving was negligible. Furthermore, as during flight, not all energy is used for mechanical work, we found a greater decrease rate of ODBA at different gliding proportions compared to heart rate. Nevertheless, the combination of the two methods is essential to determine birds' movement and energy expenditure. This study provides empirical evidence that intermittent flight is energetically beneficial and can reduce the high costs of flights. Geese Branta-Leucopsis; Doubly Labeled Water; Heart-Rate; Oxygen-Consumption; Metabolic-Rate; Expenditure; Behavior; Birds; Accelerometry; Acceleration http://creativecommons.org/licenses/by/4.0/ https://phaidra.vetmeduni.ac.at/api/object/o:2769/download 10.3389/fevo.2022.891079 https://phaidra.vetmeduni.ac.at/o:605 application/pdf Frontiers in Ecology and Evolution 10 (2022) Frontiers in Ecology and Evolution 10 486.49 kB 2022