High duty cycle moth sounds jam bat echolocation: bats counter with compensatory changes in buzz duration

Area of Science:

• Bioacoustics
• Animal Communication
• Echolocation

Background:

• Tiger moths produce ultrasonic clicks for defense.
• Higher click duty cycles are hypothesized to interfere with bat echolocation.
• The minimum duty cycle for effective sonar jamming by moths is not well understood.

Purpose of the Study:

• To investigate the relationship between tiger moth signal duty cycle and bat sonar jamming effectiveness.
• To determine if a duty cycle threshold exists for classifying moths as acoustically aposematic or sonar jammers.
• To understand bat responses to varying moth click duty cycles.

Main Methods:

• Playback experiments were conducted with three male big brown bats (Eptesicus fuscus).
• Acoustic signals from Bertholdia trigona moths with duty cycles from 0% to 46% were used to challenge bat attacks on tethered moths.
• Bat capture success and echolocation behavior were recorded.

Main Results:

• No evidence of a duty cycle threshold for sonar jamming was found.
• Sonar jamming effectiveness was a continuous function of duty cycle, increasing with more clicks during bat signal processing.
• Increased moth duty cycle significantly decreased bat capture success.
• Bats extended their terminal buzz duration in response to high duty cycles, improving capture success.
• The number of bat echolocation sound groups decreased with high moth duty cycles, but this did not impact capture success.

Conclusions:

• Tiger moth sonar jamming ability is a continuous function of duty cycle, not determined by a specific threshold.
• Moths cannot be solely classified as acoustically aposematic or sonar jammers based on duty cycle.
• Bats can compensate for moth sonar jamming by adjusting their echolocation behavior, specifically by lengthening their terminal buzz.