Echolocation calls of the Brazilian funnel-eared bat Natalus macrourus: description and effects of recording method on acoustic parameters

Abstract Bioacoustic studies of bats have advanced significantly in recent decades, driven by the popularization of ultrasonic recorders and the training of human resources; however, many species still lack detailed descriptions of their echolocation calls. We hypothesised that recording conditions (free-flight vs. flight tent) significantly alter the structure of echolocation calls. Natalus macrourus echolocation calls based on our studies of individuals in caves of Serra dos Carajás, Pará. We analyzed 89 bat passes (39 in free flight, 50 in flight tents), totaling 2,216 pulses. Natalus macrourus emits downward frequency-modulated calls with short durations. In free flight, the Frequency of Maximum Energy (FME) mostly occurred in the second harmonic (97.7% of pulses), while tent recordings showed a higher proportion of FME in the first harmonic (44.7%). Significant differences ( p < 0.01) were found in all acoustic parameters, with pulses in flight tents having longer durations, interpulse intervals, and bandwidth, as well as lower FME and maximum frequencies. Discriminant Function Analysis correctly classified 85.4% of pulses, confirming that captivity can alter call structure. Our findings advise caution when using post-capture data to characterize bat echolocation calls. Understanding the acoustic repertoire of a bat species and accurately describing and quantifying echolocation pulses opens new frontiers for research in natural history, ecology, and taxonomy.