Monitoring the singing activity of a bird community in an urban forest through the soundscape

In natural and semi-natural environments birds contribute most to the soundscape composition, especially during singing activity picks. At the same time they are subjected to the acoustic environment influence, to the extent that some of their physiological and ecological aspects can be altered. The aim of this study was to evaluate the spatial and temporal variability of the singing activity of a bird community in an urban forest in relation with increasing distances from a noise sources. The study has been conducted in a rectangular forest lot of 19 hectares in Milan (Italy) with an high-traffic highway that pass parallel to the forest border to a distance of 150 meters. Sounds were recorded with LCR recordings in 22 sites in a regular grid at an increasing distances from the highway. Each recording was  4-5 days duration and was repeated for 6 sessions from April to June. The Acoustic Complexity Index (ACI) was calculated by extrapolating the recordings from 6.30 am to 8.30 am. In addition, assisted traditional phonometric measures and traditional noise indexes (Leq and L95) were used. Methodologically, we experimented how the passive recording of environmental sounds through LCR is a non invasive survey method that allows us to obtain a considerable amount of data without disturbing or altering the birds behaviour. Results of Leq e L95 highlighted the negative relationship between vocalization abundance and proximity to a disturbance source. However, the analysis of the spatial and temporal trends of ACI did not revealed clear patterns related to the increasing of distance from the highway. This result may be due to the size of the study area (too small) and to the complexity of the environmental surroundings and  the presence of multiple noise sources. Comparison with traditional sound metrics showed that ACI is a robust index in representing and quantifying the presence of biophonies but the application in urban environment still needs further analysis.