Temperate bats may alter calls to partially compensate for weather-induced changes in detection distance

Abstract

Echolocation is the use of self-emitted calls to probe the surrounding environment. The atmosphere strongly absorbs sound energy, particularly high frequencies, thereby limiting the sensory range of echolocating animals. Atmospheric attenuation varies with temperature and humidity, which both vary widely in the temperate zone. Since echolocating insectivorous bats rely on ultrasound to capture insects, their foraging success might decrease with seasonal and daily variations in weather. To counteract weather-induced variations in prey detection, we hypothesised that European bats decrease call frequency and increase call energy when atmospheric attenuation increases, thereby maintaining their prey detection distance. Using acoustic localisation and automated call analysis, we measured call frequency and energy in free-flying bats of three common European insectivorous species. One species, Pipistrellus nathusii/kuhlii, increased call frequency, but simultaneously decreased call energy, while the two other species (P. pipistrellus and Myotis daubentonii) did not alter call parameters. We estimated the detection distance for prey based on the recorded call parameters and prey characteristics, using a custom-developed theoretical model. None of the three species maintained prey detection distance (it decreased by 1.7 to 3.4 m) when atmospheric attenuation increased. This study contributes to a better understanding of the sensory challenges faced by animals in fluctuating environments.

Variation in echolocation call emission of Neotropical insect-eating bats in response to shifting ambient temperatures

“…While most studies to date have investigated how bats may adapt frequency and source level to deal with changes in AA and other auditory challenges (de Framond, Reininger, et al, 2023;Snell-Rood, 2012;Surlykke & Kalko, 2008), only few have considered the effect of changing call duration on sound perception and detection distance (but see Chaverri & Quirós, 2017;Luo et al, 2014;Schmidt & Thaller, 1994). Our study provides additional support that adjusting call duration is another potential mechanism to improve signal detection.…”

“…Similarly, bats may experience trade-offs when (strongly) reducing call frequency. By lowering call frequency, bats can increase detection distance, but in parallel confine prey-detection to larger items because smaller objects reflect lower frequencies less (de Framond, Reininger, et al, 2023;Jung et al, 2014).…”

“…We used this information to determine an appropriate bandpass filter for every recording session for final call analysis. We used the customdeveloped TOAD Suite software package (de Framond, Beleyur, et al, 2023;de Framond, Reininger, et al, 2023;Hügel et al, 2017;Lewanzik & Goerlitz, 2018) for MATLAB (Version R2007b; The Mathworks, Inc., Nattick (MA), USA) to calculate the bats' spatial position for each emitted signal based on the time-of-arrival differences (TOAD) from the central to the outer microphones of the array (Koblitz, 2018) and the speed of sound for the current air temperature and relative humidity.…”

“…Target strength is strongly influenced by prey size (de Framond, Reininger, et al, 2023), its orientation towards the bat (Sümer et al, 2009;Waters et al, 1995), and surface properties (Neil et al, 2020a;Simon et al, 2023). In general, neotropical vespertilionid species prefer soft prey like nocturnal lepidoptera (moths) from a wide range of sizes (Aguirre et al, 2003;Ingala et al, 2021).…”

“…To date, studies focusing on sensory responses of bats to fluctuations in atmospheric conditions on a short temporal scale are scarce. Some studies have assessed effects on detection distance (de Framond, Reininger, et al, 2023) and adjustments in echolocation calls in a temperate region (Snell-Rood, 2012). To our knowledge, only one study has evaluated the association between weather conditions and acoustic parameters of calls in echolocating Neotropical bats (Chaverri & Quirós, 2017).…”