Abstract
Ambient noise can cause birds to adjust their songs to avoid masking. Most studies investigate responses to a single noise source (e.g., low-frequency traffic noise, or high-frequency insect noise). Here, we investigated the effects of both anthropogenic and insect noise on vocalizations of four common bird species in Hong Kong. Common Tailorbirds (Orthotomus sutorius) and Eurasian Tree Sparrows (Passer montanus) both sang at a higher frequency in urban areas compared to peri-urban areas. Red-whiskered Bulbuls (Pycnonotus jocosus) in urban areas shifted the only first note of their song upwards. Swinhoe’s White-eye (Zosterops simplex) vocalization changes were correlated with noise level, but did not differ between the peri-urban and urban populations. Insect noise caused the Eurasian Tree Sparrow to reduce both maximum, peak frequency, and overall bandwidth of vocalizations. Insect noise also led to a reduction in maximum frequency in Red-whiskered bulbuls. The presence of both urban noise and insect noise affected the sound of the Common Tailorbirds and Eurasian Tree Sparrows; in urban areas, they no longer increased their minimum song frequency when insect sounds were also present. These results highlight the complexity of the soundscape in urban areas. The presence of both high- and low-frequency ambient noise may make it difficult for urban birds to avoid signal masking while still maintaining their fitness in noisy cities.
Highlights
Avian acoustic signals are important for mate attraction, territorial defense, alarm signaling and other functions vital for survival and fitness (Collins 2004, Catchpole and Slater 2008, Bradbury and Vehrencamp 2011)
The most commonly documented responses of birds to low frequency anthropogenic noise are to increase song frequency and/or amplitude in order to avoid signal masking (e.g. Slabbekoorn and Peet 2003, Brumm 2004, Wood and Yezerinca 2006, Slabbekoorn 2013, Guo et al 2016, could be directly linked, with birds singing louder singing at higher frequencies as a correlated response, rather than an independent change (Brumm and Zollinger 2011, Zollinger et al 2012, Zollinger et al 2012); or higher frequencies may be used by birds as these frequencies allow greater amplitude (Nemeth et al 2013)
The average cicada noise frequency was significantly higher in peri-urban area
Summary
Avian acoustic signals are important for mate attraction, territorial defense, alarm signaling and other functions vital for survival and fitness (Collins 2004, Catchpole and Slater 2008, Bradbury and Vehrencamp 2011). To avoid masking by noise, species may alter their. To date many species of birds have been shown to alter their vocalizations to avoid signal overlap with abiotic (e.g. rushing water, Pytte et al 2003), or biotic factors; such as the songs of other birds (Planqué and Slabbekoorn 2008), insect sounds (Slabbekoorn and Smith 2002, Dingle et al 2008, Kirschel et al 2009, Luther 2009, Hart et al 2015, Stanley et al 2016) and amphibian choruses (Lenske and La 2014). The most commonly documented responses of birds to low frequency anthropogenic noise are to increase song frequency and/or amplitude in order to avoid signal masking Several studies have shown that birds decrease the frequency of their vocalizations in response to high-frequency noise; suggesting that frequency responses can be independent of adjustments of amplitude (Great Tits, Parus major, Halfwerk and Slabbekoorn 2009; Black capped chickadees, Poecile atricapillus, Courter et al 2020)
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