Choosing the 'correct' bat detector

Direct field comparisons revealed that in any time period, a bat detecting system using zero-crossing period meter analysis (the Anabat II Bat Detecto r with Anabat ZCAIM and Anabat 6 software) detected significantly fewer bat echolocation calls than a time-expansion bat detecting system (Pettersson D980 detector with BatSoundPro software). Furthermore, the features of 81 e cholocation calls (highest frequency, in kHz; lowest frequency, in kHz; dur ation, in ms) recorded and analyzed on both systems differed significantly. Regression analyses indicated no consistent, frequently unpredictable diff erences between Anabat and Pettersson values for the lowest frequencies in echolocation calls, but a significant correlation for their highest frequen cies and durations. In a variety of field settings in Israel and in souther n Ontario, Canada involving both foraging bats and bats emerging from a cav e roost, the Pettersson system recorded echolocation calls not detected by the Anabat system. When many Myotis bats were emerging from a cave roost in Israel, the Anabat system did nor detect the calls of a Rhinolophus specie s or those of another vespertilionid which were detected by the Pettersson system. The differences in performance between the two kinds of systems ref lect differences in sensitivity and operation between zero-crossing period meters and time-expansion systems. Data on bat activity or echolocation cal ls detected and analyzed by a zero-crossing period meter system like Anabat are not as consistent or as reliable as those obtained by a time-expansion system like the Pettersson. Differences in performance of bat detectors co incide with considerable difference in costs, from about US$ 650 for an Ana bat system, to over US$ 2,000 for a Pettersson system, which involves digit al time-expansion. A time-expansion system involving a high speed tape reco rder will cost over US$ 30,000. When it comes to bat detectors and analysis systems, the quality of data that will be obtained is a direct reflection of cost - buyers get what they pay for.