The Influence of Relative Biologger Weight and Total Mass on the Flight Behaviour of the Lesser Noctule (Nyctalus leisleri)

Biologging devices (tags) are a valuable tool for studying an animal’s behaviour, however the impact on animals carrying them, have not yet been fully quantified. The wide range of tagged animals requires species specific guidelines such as weight limits of tags. This study contributes to the understanding tag effects on animals by testing the effect of additional weight on small flying animals and furthermore establishing a method of speed calculation by video analysis. In this thesis, four individuals of lesser noctules (Nyctalus leisleri) were equipped with small interchangeable weights and tested for their change in straight flight speed as a reaction to additional mass. Speed calculations were estimated from 3D trajectories of bats flying in a flight tunnel made from six synchronised videos of the same flight. The range of relative tag mass (2-12%) did not result in a significant effect between relative tag- or total mass on straight flight speed across the four individuals, possibly due to individual flight preferences and imprecise measurements of flight speed. While this method of speed calculation by video analysis proved to be effective, further refinement is needed to be fully reliable.