Abstract
I conducted a study of the effects of stream noise on local bird distribution in the breeding and wintering seasons between 2009 and 2012 in Oyama-sawa of Chichibu, Saitama Prefecture, central Japan. I set three study sites, each of which included survey points with and without stream noise, and counted the abundance of bird species within a radius of 50m. The general character of each study site was similar in terms of vegetation type and density. The sound levels (sound pressure waves) at each survey point were characterized by frequency and decibel range on an unweighted decibel scale. Sonagrams for the bird species encountered were created from data obtained during the study. In the breeding seasons, the number of Sakhalin Leaf-warblers Phylloscopus borealoides was significantly greater in the sites with stream noise, but the numbers of Eurasian Nuthatches Sitta europaea and Coal Tits Periparus ater were significantly greater in the sites free from stream noise. There was no significant difference in abundance between Eurasian Wrens Troglodytes troglodytes and Blue-and-White Flycatchers Cyanoptitla cyanomelana. In the wintering seasons, however, the abundances of Eurasian Nuthatches, Coal Tits and Willow Tits Poecile montanus showed no significant difference between the sites with and without stream noise. Sakhalin Leaf-warblers sang at frequencies higher than 6000Hz, which is little affected by the stream noise. Eurasian Nuthatches and Coal Tits, on the other hand, sang at lower frequencies than 6000Hz, which is greatly affected by the noise. Bird species that sang in a similar frequency range to the loudest stream noise (as measured by dB) demonstrated a shift away from the streams during the breeding season, while birds that sang in a higher frequency, at which the streams produce less noise, appear to either prefer near-stream locations or do not demonstrate a shift between sites. These results suggest that the stream noise may affect the local bird distribution in the breeding period through hindering the song communication.
