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Ambient noise can interfere with signal transmission and detection across many taxa and modalities. Evidence suggests that, over time, signals evolve to minimize interference from ambient noise and other signalling animals. Less well studied is the possibility of short-term behavioural responses to transient ambient noise, in which animals actively adjust signal parameters to recover signalling efficacy. Here we test animals'' capacity to adjust vocal signal parameters in the face of transient acoustic interference. In field trials we monitored the songs of territorial male black-capped chickadees, Poecile atricapillus, determined the frequencies of their ‘fee-bee’ songs, and broadcast tones to closely mask subjects'' ‘bee’ notes. We also presented control nonmasking tones of 5kHz, well above birds'' song frequencies. Our main finding was that males responded to masking tones by shifting song frequencies after an average of 66.4s from tone onset, whereas frequency shifts in the presence of nonmasking tones occurred only after an average of 95.8s. The quicker shift in frequencies in the face of masking noise provides new evidence for vocal behavioural plasticity, and further reveals how behavioural plasticity together with evolutionary adaptations can minimize the detrimental effects of ambient noise on communication. [Copyright &y& Elsevier]

Noise may drive changes in the composition and abundance of animals that communicate vocally. Traffic produces low-frequency noise (<3 kHz) that can mask acoustic signals broadcast within the same frequency range. We evaluated whether birds that sing within the frequency range of traffic noise are affected by acoustic masking (i.e., increased background noise levels at the same frequency of vocalizations reduce detection of vocalization) and are less abundant in areas where traffic noise is loud (44-57 dB). We estimated occupancy, the expected probability that a given site is occupied by a species, and detection probabilities of eight forest-breeding birds in areas with and without traffic noise as a function of noise and three measures of habitat quality: percent forest cover, distance from plot center to the edge of forest, and the number of standing dead trees or snags. For the two species that vocalize at the lowest peak frequency (the frequency with the most energy) and the lowest overall frequency (Yellow-billed Cuckoo [Coccyzus americanus ] and White-breasted Nuthatch [Sitta carolinensis ]), the presence of traffic noise explained the greatest proportion of variance in occupancy, and these species were 10 times less likely to be found in noisy than in quiet plots. For species that had only portions of their vocalizations overlapped by traffic noise, either forest cover or distance to forest edge explained more variation in occupancy than noise or no single variable explained occupancy. Our results suggest that the effects of traffic noise may be especially pronounced for species that vocalize at low frequencies. [ABSTRACT FROM AUTHOR]