11.07.2022: Many birds utilise a mode of flight known as intermittent flight in which phases of flapping, during which the birds gain height, alternate with gliding phases. Using data from GPS transmitters, a research team led by Vetmeduni, in collaboration with the Waldrappteam conservation project in Tyrol, the Swiss Federal Institute of Technology (ETH Zurich), the University of Vienna, and the Faculty of Veterinary Medicine at the University of Bern (Vetsuisse), has gathered the first empirical evidence showing that bald ibises use intermittent flight to significantly reduce their energy requirements.
Birds have exceptionally high energy demands during flight. One visible feature of some species is a mode of flight in which the birds alternate between flapping and gliding, which has been postulated as a strategy for saving energy. To date, however, there has been no empirical evidence for an energetic benefit of intermittent flight. To better understand the energetic costs involved, the researchers equipped hand-raised northern bald ibises (Geronticus eremita) with GPS data loggers during migration to monitor the birds’ position, wing beats, overall dynamic body acceleration and heart rate as indicators of energy expenditure.
Gliding along instead of hurrying about
The study’s first author, Ortal Mizrahy-Rewald from the Research Institute of Wildlife Ecology at Vetmeduni and a member of the Waldrappteam conservation project in Mutters, Tyrol, comments on the central findings of the research project: “The energy expenditure is significantly affected by the length of flapping and gliding bouts. A pronounced decrease in heart rate was measured after already one second of gliding. Additionally, the heart rate during flapping bouts of up to 30 seconds increased steadily but stabilised thereafter.”
20% gliding equals energy savings of more than 10%
The gilding proportion during intermittent flight had a significant impact on energy savings compared to continuous flapping: “At a gliding proportion of about 20%, we measured a maximum savings of 11% based on heart rate measurement. At higher gliding proportions, the additional energy savings were negligible,” says the study’s last author, Thomas Ruf from the Research Institute of Wildlife Ecology at Vetmeduni. According to Ruf, the combined measurement of heart rate and overall dynamic body acceleration (ODBA) is key to properly assessing the birds’ movements and their energy expenditure.
Ambitious EU resettlement project
The northern bald ibis (Geronticus eremita) is a migratory bird about the size of a goose that was once widespread in Central Europe but has been extinct in most of its former range since the 17th century due to extensive hunting pressure. Under the European Union’s LIFE+ biodiversity programme, and with the support of WWF and other conservation groups, endeavours are being made to reintroduce the bald ibis as a migratory bird in Central Europe, Spain and Italy. Originally started by the Konrad Lorenz Research Centre in Grünau, Upper Austria, the Waldrappteam conservation project has since launched several reintroduction efforts. Northern bald ibis are now being bred and raised in zoos across Austria before they are guided across the Alps to their wintering sites in Italy. The following spring, they fly back north as a group without human assistance.
The article “Empirical Evidence for Energy Efficiency Using Intermittent Gliding Flight in Northern Bald Ibises” by Ortal Mizrahy-Rewald, Elisa Perinot, Johannes Fritz, Alexei L. Vyssotski, Leonida Fusani, Bernhard Voelkl and Thomas Ruf was published in Frontiers in Ecology and Evolution.
Scientific paper
