In addition to researchers from the universities of Jyväskylä and Helsinki, the international study involved researchers from over thirty countries. Samples were collected by automatic recorders from 139 locations over several years.
People hear birds singing late at night and early in the morning
From the collected audio material, researchers analysed various descriptive indicators. For example, they examined the amount of sound energy present in low and high frequencies, as well as the variation in the sounds. The sounds were also classified into different categories, including human speech, vehicle sounds, and natural sounds such as rain and wind. Bird species were also automatically identified based on the sounds they produce.
"The collected sound data provides evidence of predictable rhythms in nature," says University Researcher Panu Somervuo from the University of Helsinki. "For example, birds sing most actively in the morning and evening as well as in spring."
Birds are an important part of urban green spaces
One of the most surprising findings of this study was that the number of bird species in urban green areas was, on average, greater than in natural environments.
"Green areas are often highly diverse, so a one-hectare monitoring plot can serve as a habitat for several bird species," says Academy Professor Otso Ovaskainen from the University of Jyväskylä. "However, this does not mean that natural areas in their original state are unimportant to birds, since species living there cannot be found in urban areas."
The study was published in the prestigious Nature Ecology & Evolution series.
