Data from: Multiple constraints on urban bird communication: both abiotic and biotic noise shape songs in cities

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.