08.05.2023: Biologging devices are often attached to birds for research purposes and to collect important data. Now a team of researchers led by the University of Veterinary Medicine Vienna has investigated the aerodynamic effect of biologgers with northern bald ibis, an endangered species of bird, in a wind tunnel. The results showed that biologging devices significantly influence energy expenditure and flight distances, and that aerodynamic optimizations and proper positioning on the birds’ bodies can significantly reduce the detrimental effects.
There has been little scientific research to date regarding the impact of biologgers on animal aerodynamics and hydrodynamics. This stands in marked contrast to the increasingly extensive use of such technologies in wild-living animals. Recently, there have been growing concerns about the detrimental effects that these devices may have on the animals involved.
While the focus in biologging has long been solely on reducing weight, the researchers in this study investigated the aerodynamic effects of the devices. For this purpose, the northern bald ibises (Geronticus eremita) were trained to fly in a wind tunnel where heart rate and dynamic body acceleration (VeDBA) were measured as parameters for energy expenditure in relation to different logger shapes and wind flow directions.
The perfect biologger: attached to the back of the body and aerodynamically shaped
“Our data demonstrates that the position of biologging devices significantly influences the flight distances, and that shape has a considerable effect on energy expenditure. Unfavourable shape and positioning not merely affect the amount of energy expended during flapping flight; the energetically probably more important effect is that the devices impair the bird’s ability to glide or soar, which forces them to perform the energetically much more demanding flapping flight more frequently,” says the study’s first author, Ortal Mizrahy-Rewald from the Research Institute of Wildlife Ecology at Vetmeduni, summarizing the key findings of the study.
A complementary study with wild-living northern bald ibis during spring migration demonstrates that the position of the devices on the birds’ backs affects the length of the flight stages. “Birds that carried the devices on the upper back had significantly shorter flight stages compared to birds with a device positioned further towards the tail,” as Mizrahy-Rewald explains.
Little effort required to reduce detrimental effects
According to the researchers, the detrimental effects can be reduced with relatively little effort through a strictly aerodynamic design of the housing and increased consideration of aerodynamics when attaching the device to the animal’s body. In birds, the attachment of biologging devices via leg loops to the lower back is clearly preferable to the common attachment method via wing loops on the upper back. Nevertheless, the importance of drag reduction may vary between systems, as the benefits of having a biologging device close to the centre of gravity may outweigh the increase in drag that this involves.
The article “The impact of shape and attachment position of biologging devices in Northern bald ibises” by Ortal Mizrahy‑Rewald, Natalie Winkler, Frederik Amann, Katharina Neugebauer, Bernhard Voelkl, Herwig A. Grogger, Thomas Ruf and Johannes Fritz was published in Animal Biotelemetry.