Abstract
Frequency shifts in signals of bats flying near conspecifics have been interpreted as a spectral jamming avoidance response (JAR). However, several prerequisites supporting a JAR hypothesis have not been controlled for in previous studies. We recorded flight and echolocation behavior of foraging Pipistrellus pipistrellus while flying alone and with a conspecific and tested whether frequency changes were due to a spectral JAR with an increased frequency difference, or whether changes could be explained by other reactions. P. pipistrellus reacted to conspecifics with a reduction of sound duration and often also pulse interval, accompanied by an increase in terminal frequency. This reaction is typical of behavioral situations where targets of interest have captured the bat’s attention and initiated a more detailed exploration. All observed frequency changes were predicted by the attention reaction alone, and do not support the JAR hypothesis of increased frequency separation. Reaction distances of 1–11 m suggest that the attention response may be elicited either by detection of the conspecific by short range active echolocation or by long range passive acoustic detection of echolocation calls.
Highlights
Frequency shifts in signals of bats flying near conspecifics have been interpreted as a spectral jamming avoidance response (JAR)
In search flights echolocation signals with durations of up to 9 ms were emitted at pulse intervals around 90 ms, most likely in the rhythm of wingbeat
Neither in encounters nor in pursuits we found any significant correlation between changes in echolocation behavior and flight path angles to the conspecific (Spearman’s rank correlation, all p-values > 0.07 for sufficient sample sizes)
Summary
Frequency shifts in signals of bats flying near conspecifics have been interpreted as a spectral jamming avoidance response (JAR). Reaction distances of 1–11 m suggest that the attention response may be elicited either by detection of the conspecific by short range active echolocation or by long range passive acoustic detection of echolocation calls Both technical and biological active sensing systems such as radar, sonar, and echolocation in bats and cetaceans are based upon the same principle; a sender transmits signals and a receiver analyzes the returning echoes to detect, localize, and classify targets of interest. An increase of the terminal frequency in echolocation signals of flying bats in response to playback signals was considered evidence of a spectral jamming avoidance response (JAR) in T. brasiliensis[11], and in Pipistrellus abramus[12]. Long pulse intervals in E. fuscus (>200 ms) when flying with www.nature.com/scientificreports/
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