Effects of signal features and environmental noise on signal detection in the great tit, Parus major

Environmental noise caused by human activities may hamper acoustic communication in animals. Field studies in urban environments suggest that birds may alter their communicative behaviour in response to noise, but there is little experimental evidence for a detrimental effect of urban noise on perception. We investigated the masking effects of urban noise on signal detection using operant tests with great tits in the laboratory. We compared masking effects induced by urban noise, woodland noise and a typical dawn chorus, including a variety of singing birds. Maskers were presented at their natural sound pressure level and masking conditions were compared to a silent no-masker condition. The signals to be detected were composed of artificial sinusoids and noise bands mimicking signal features of natural great tit song elements. Both masker condition and signal feature significantly affected signal detection in the captive great tits. Deteriorated auditory thresholds in woodland and urban noise required the signal to be on average 12 dB and 18 dB louder than in the no-masker condition, respectively. The dawn chorus masker showed the most dramatic shift in auditory threshold of about 29 dB. Signals with the sound energy concentrated within a narrow frequency range were on average easier to detect than signals spread over a wide frequency range. Our perceptual results provide insight into how birds may counteract negative masking effects by singing song elements with specific features.