NBIs in a wind tunnel
Newsletter 17/09/2019
A completely different perspective on bird flight: This year, four Northern Bald Ibises from the Zurich Zoo were hand-raised by Katharina Neugebauer and Frederik Amann. At the end of July, the four birds and their foster parents moved with to Seekirchen am Wallersee in Austria. Since July, a wind tunnel specially adapted to the requirements of NBIs has been set up in an abandoned stable.
The wind tunnel was planned and constructed at the FH Joanneum in Graz under the direction of Prof. Herwig Grogger. It has a length of 8.5 m, with an outlet opening of 2.5 x 1.5 m. 8 fans accelerate the air up to 55 km/h and transport an air volume of 205,000 m³ per hour.
In this project, we are pursuing two particular goals: Firstly, we aim to collect data in the context of the current Austrian research project FWF P 30620-BBL in order to investigate the function and energetics of the formation flight in migratory birds. Previous studies (including Portugal et al. 2014, Völkl & Fritz 2017) have shown that NBIs are coordinating their formation flight in a very precise way and are therefore able to save energy. Now we want to find out how much energy can actually be saved when flying in formation and how this complex social behaviour is working. During the human-led migration in 2019, large amounts of data were already collected, which are now complemented by further data collected in the wind tunnel. The two PhD students Elisa Perinot and Ortal Rewald are responsible for this data acquisition; they are supervised by Bernhard Völkl (University of Bern), Leonida Fusani and Thomas Ruf (both University of Veterinary Medicine Vienna).
Recently, a prestigious ornithological journal reported that research on harmful effects of transmitters mounted on various bird species did not show any results of concern. That does not correspond to our experiences. On the contrary, the potentially harmful effects we observe are manifold. In particular, in our experience, the aerodynamic cost of a transmitter mounted on a bird is often underestimated or ignored. Therefore, our second goal is the measurement and visualisation of these effects in the wind tunnel in order to optimise both the housing shapes and the positioning of the transmitters on the bird's body. These results are of great importance for the reintroduction of the NBIs. In addition, they should also help to minimize the negative consequences when transmitters are mounted on other wild bird species.
Why are those analyses done with NBIs? Because their reintroduction, and more recently also the possibility to let some of them fly in a wind tunnel, are offering unique and ideal conditions for this kind of research.
The basic requirement for a successful data acquisition is that the birds are able to fly in a relaxed and unforced way in the wind tunnel. Obviously, Katharina and Frederik, assisted by the former foster mother Corinna Esterer, were able to create the ideal conditions to achieve that goal. The birds are very relaxed during their training and respond very well to their two foster parents. Training is well advanced, as can be seen in these video sequences. At the beginning of October, we’ll start the data collection. After that, in the upcoming year, the four NBIs will be integrated in the release population as part of the breeding group.
Picture: Frederik Amann and Katharina Neugebauer with the NBI “Nestroy” in the wind tunnel. In the background you can see the eight big fans. They accelerate the air up to 55 km/h; the NBI is able to fly between 40 and 50 km/h.
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