The Solent coastline hosts thriving harbours, ports and other coastal industry, meaning there is a high volume of anthropogenic activity interacting with the marine environment. Most of this activity creates a level of noise that can lead to the disturbance and displacement of Special Protection Area (SPA) bird features.
Noise monitoring results from both long-term and short-term monitoring during the overwintering period in nine key areas across SPA sites in the Solent are presented to provide data on background noise levels as well as some understanding of the likely triggers for bird responses to noise in the area.
The background noise levels are represented using the sound index LA90 which describes the sound level at which is exceeded for 90% of the measurement period. The daytime background noise levels in the nine study areas range between LA90,16hours 43.0 dB(A) to 49.0 dB(A) with the exception of one location where the daytime background noise level is LA90,16hours 69.0 dB(A) which is likely to be due to traffic noise.
The results from the short-term noise monitoring show there is no obvious correlation between specific sound frequencies and bird responses. However, the sound pressure level at each frequency is generally above the background noise level. The results also show that birds are more likely to respond to noise disturbance when the sound pressure levels at the location of the birds are at least 20.0 dB(A) above the background noise level. However, the visual nature of the noise disturbance is also likely to cause bird responses.