DOI: 10.5061/dryad.b4f2m1t
title: Data from: Why does noise reduce response to alarm calls? Experimental assessment of masking, distraction and greater vigilance in wild birds

description: 1. Environmental noise from anthropogenic and other sources affects many
 aspects of animal ecology and behaviour, including acoustic communication.
 Acoustic masking is often assumed in field studies to be the cause of
 compromised communication in noise, but other mechanisms could have
 similar effects. 2. We tested experimentally how background noise
 disrupted the response to conspecific alarm calls in wild superb
 fairy-wrens, Malurus cyaneus, assessing the effects of acoustic masking,
 distraction and changes in vigilance. We first examined the birds’
 response to alarm-call playbacks accompanied by different amplitudes of
 background noise that overlapped the calls in acoustic frequency. We then
 scored and videoed their response to alarm calls in two types of
 background noise, that did or did not overlap call frequency, but were
 broadcast at a constant amplitude. 3. Birds were less likely to flee to
 alarm calls in higher amplitudes of overlapping noise, demonstrating that
 noise itself compromised communication independently of environmental
 correlates. Background noise affected the response only if it overlapped
 in frequency with the alarm calls, implying that the effect was not due to
 distraction. Further, birds were equally vigilant during background noise
 of overlapping or non-overlapping frequency, indicating that the lack of
 response to alarm calls in overlapping noise was not due to enhanced
 vigilance and awareness that there was no predator. 4. We conclude that
 alarm-call reception was compromised by masking, a mechanism that is often
 assumed but rarely tested in an ecological context. Masking compromised
 reception of high-frequency ‘aerial’ alarm calls and so could reduce
 survival in background noise of similar frequency. While anthropogenic
 noise, which is often of lower frequency, is unlikely to affect
 communication with these calls, it could affect reception of acoustic cues
 of danger, or other conspecific or heterospecific alarm calls.
description: Dryad Exp 1 Zhou et
 alResults of Experiment 1,
 examining the effects of playback of noise of different amplitudes on the
 response to aerial alarm calls. The noise overlapped the frequency of the
 alarm calls (6–10 kHz; alarm call peak frequency mean 9.1 kHz). Noise
 amplitudes ranged from 52–61 dB at 10 m, while alarm calls were broadcast
 at 52 dB at 10 m. Each location received a unique set of every type of
 playback. Playbacks included alarm calls mixed with noise, and control
 playbacks of noise alone or alarm calls alone. The amplitude of ambient
 noise was measured after each playback.Dryad Exp 2 Zhou et
 alData for Experiment 2,
 examining the effect of noise of different frequencies, but constant
 amplitude (58 dB at 10 m), on the response to aerial alarm calls (52 dB at
 10 m). Alarm calls have a mean peak frequency of c 9.1 kHz. Noise was of a
 frequency that either overlapped with the alarm calls (6–10 kHz) or did
 not overlap the alarm calls (2–6 kHz). The data also include the
 proportion of time the focal bird had its head up in the 10 s of noise
 immediately before the alarm call. Each location received a unique set of
 every playback type. Playbacks included alarm calls mixed with noise, and
 control playbacks of noise alone or alarm calls alone. The amplitude of
 ambient noise was recorded after each playback.