The effect of temporal masking on alarm call communication in wild superb fairy-wrens

Abstract

Noise from human activity is a global concern that threatens wildlife, including by disrupting acoustic communication. This disruption appears predominantly caused by masking, where noise makes it difficult to hear acoustic signals. Previous studies have found a strong masking effect when noise and signals occur simultaneously. However, noise can also have a temporal masking effect, meaning that the signal is not detected even if noise occurs before or after the signal (forward and backward masking, respectively). As background noise is often intermittent, temporal masking by natural sounds and anthropogenic noise could pose a significant challenge for animal communication. Surprisingly, although commonly found in humans, temporal masking has been rarely studied in other species. To investigate whether temporal masking affects bird communication in the wild, we conducted a playback experiment on superb fairy-wrens, Malurus cyaneus, using single-element alarm calls before, during and after filtered white noise, as well as a control playback of alarm calls alone. We found that fairy-wrens stopped responding to alarm calls during noise, showing simultaneous masking, but were equally likely to flee if there was noise immediately before or after an alarm call as when there was no noise, suggesting a lack of temporal masking. However, among those fairy-wrens that fled, there was a 20 ms delay in the response to alarm calls after the noise, possibly because of subtle forward masking that delayed call reception. We conclude that temporal masking is unlikely to stop fairy-wrens’ fleeing to alarm calls but might slightly delay call reception. We urge further studies of temporal masking in other species, using various sources of natural and anthropogenic noise, as only then will we know whether temporal masking is of general significance in compromising animal communication.