Abstract
Unmanned aerial vehicles (UAVs) are rising in popularity for wildlife monitoring, but direct recordings of animal vocalizations have not yet been accomplished, likely due to the noise generated by the UAV. Echolocating bats, especially Tadarida brasiliensis, are good candidates for UAV recording due to their high-speed, high-altitude flight. Here, we use a UAV to record the signals of bats during morning roost re-entry. We designed a UAV to block the noise of the propellers from the receiving microphone, and report on the characteristics of bioacoustic recordings from a UAV. We report the first published characteristics of echolocation signals from bats during group flight and cave re-entry. We found changes in inter-individual time-frequency shape, suggesting that bats may use differences in call design when sensing in complex groups. Furthermore, our first documented successful recordings of animals in their natural habitat demonstrate that UAVs can be important tools for bioacoustic monitoring, and we discuss the ethical considerations for such monitoring.
Highlights
As Unmanned aerial vehicles (UAVs) technology has become more accessible, many biologists are turning to these airborne platforms for wildlife recording[1] to conduct surveys of birds[2,3,4,5], reptiles[6], fish[7], and mammals[8,9,10,11]
The purpose of this study was to use UAV technology to conduct acoustic recordings from bats during re-entry to examine if call parameters change according to flight altitude
We report on two key findings: animal vocalizations recorded from a UAV, and the first published description of bat echolocation parameters during cave re-entry when bats are flying in groups
Summary
As UAV technology has become more accessible, many biologists are turning to these airborne platforms for wildlife recording[1] to conduct surveys of birds[2,3,4,5], reptiles[6], fish[7], and mammals[8,9,10,11]. Echolocating bats, the Brazilian free-tailed bat (Tadarida brasiliensis), are excellent animals for UAV recording These bats produce ultrasonic, FM signals while flying at high speeds[15,16] and high altitudes[17], and utilize a flexible echolocation system that adapts to flight behavior and target range[18,19,20]. Brazilian free-tailed bats are social animals, forming large colonies numbering in the millions[21], and demonstrate complex group dynamics[22], including rapid, irregular flight at estimated speeds up to 128 km/h during morning roost re-entry as bats descend from the sky[15]. We consider our data an initial dataset for acoustic behavior during high-speed roost re-entry while flying in groups, and expect additional datasets of acoustic re-entry to demonstrate further variation in call parameters
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