How kestrels counter chaotic currents

In a laboratory in the Linnaeusborg, an American kestrel can be seen ‘hanging’ motionless in front of a wind tunnel from which air is being blown. He appears to be coping effortlessly with the actively generated turbulence he faces. He is nicely coloured, elegant, and relatively small for a bird of prey. Next to him in the flying area are biotechnician (and bird trainer) Josien Janssen and Professor in Biomimetics David Lentink. Lentink’s ambition is to use knowledge about birds’ flight behaviour to improve the flight performance of aeroplanes and drones.

Birds flap, swoop, and skim through the air. They ‘stand’, climb, descend, hover, or glide. But how do they do it? This question has haunted David Lentink since childhood. He believes that gaining a better understanding of the highly complex flight behaviour of birds could be the key to improving the flight performance of aeroplanes and drones. With their heavy, rigid wings, aeroplanes and drones do not cope well with turbulence, whereas birds’ wings comprise such an ingenious network of delicate bones, muscles, and feathers that they can make countless minute adjustments.

Lentink is one of a rare breed: a researcher who is both an engineer and a zoologist. Having studied Aerospace Engineering at Delft University of Technology, his childhood fascination with biology drew him into a PhD in Zoology at Wageningen University, specializing in biological flight. He went on to gain even more specialist knowledge and experience in the training of birds during his postdoc at Harvard University and then at his own lab at Stanford. This diverse academic background places Lentink in a unique position in the scientific community.  

Lentink and his team are keen to discover how American kestrels manage to hover so steadily in severe turbulence. The team’s technician has built a turbulence grid, based on Lentink’s own design. The researchers place the grid in the airflow and generate various forms of turbulence by continuously adjusting the position of the series of flaps in the grid. Biotechnician Janssen then places markers on different parts of the birds’ wings and sends them into the turbulent conditions, rewarding them with their favourite snack afterwards. ‘The birds enjoy the process’, Lentink says, ‘and it provides us with lots of quantitative data on how they use their wings and tails to maintain flight stability.’ Data that PhD student Rens de Boer can use for his research.

To train birds of prey for this research, Janssen uses positive reinforcement as part of her own unique method of interacting with the birds. ‘Her method takes our research to a higher level,’ explains Lentink, ‘allowing us to acquire in-depth biological and mechanical knowledge about kestrels’ flight.’ 

^{Text: Fenneke Colstee, UG Corporate Communication
Photos: Reyer Boxem}

Further information

• David Lentink