Identify Horseshoe Bat Calls

Horseshoe bat calls consist of prolonged (up to 50 msec or more) whistling sounds at a near constant frequency. Doppler shift causes the pitch of the sound to fluctuate. The calls are narrowband, and will therefore be heard only when the detector is tuned very close to the peak frequency of the call (or sometimes to half that frequency). At other frequencies, nothing will be heard. The calls are also very directional, and will be loud only when the bat is flying directly toward the bat detector.