This is a Nathusius bat (Pipistrellus Nathusii) flying, and not at all stressed.
Researchers Sara Troxell and Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research in Germany recently tested a number of the bats in the field and in wind tunnels to determine the energy they expended while aloft.
They discovered, in effect, that they are equipped with a form of cruise control. In different circumstances, the animals all selected the flight speed that would allow them to cover maximum distance and minimum energy cost.
For the Nathusius bat, the optimal flight speed was around 27 kilometres an hour. The species, which is resident in Europe, is known to undertake journeys of as long as 2000 kilometres to reach hibernation sites.
The research is published in the Journal of Experimental Biology.