Data from: Why does noise reduce response to alarm calls? Experimental assessment of masking, distraction and greater vigilance in wild birds

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.