© Marcel Burkhardt
Bruderer, B. & A.G. Popa-Lisseanu (2005)
Radar data on wing-beat frequencies and flight speeds of two bat species.
Acta Chiropterol. 7: 73–82
This paper presents for the first time radar recorded flight paths and wing-beat pattern of two identified Palaearctic bat species. Simultaneous film recordings confirm the wing-beat pattern reflected by echo signatures. Our results suggest that discrimination of bats and nocturnally migrating birds is usually possible because the recorded bats differed from the regular flapping and pausing phases in passerines´ bounding flight as well as from the regular continuous wing-beats of other nocturnal migrants (e.g., waders and waterfowl) by very short and irregularly distributed glides (flap-gliding). Small, medium and large bats may be differentiated according to wing-beat frequency. For the discrimination of the similarly sized Nyctalus noctula and Eptesicus serotinus (both with mean frequencies of 7-7.5 Hz and variation mainly between 6 and 8 Hz) ecological or behavioural features must be included. The lowest rates of flapping (even below 5 flaps per second) occurred because some flaps were prolonged by very short glides. Measured flight speeds (13.5 and 13.2 m/s, respectively) were higher than most of the previously recorded or predicted speeds. In comparison to other methods, radar studies have the potential to be applied to bats in free flight over relatively large distances. A limitation of the radar method is given by the fact that very low flying targets cannot be tracked because they merge with ground echoes.
Key words: Nyctalus noctula, Eptesicus serotinus, flight behaviour, wing-beat pattern, speed, radar tracking