Bird song in Europe and North America may be becoming quieter and less diverse as bird populations decline, which is detrimental to ecological diversity and may also have a negative effect on human health and well-being.
Natural soundscapes are key to connecting people to nature, which has been proven to benefit both our physical and mental health. Bird calls, whistles and squawks are prominent in these soundscapes.
Simon Butler and colleagues at the University of East Anglia in Norwich, U.K., compiled bird count data from 202,737 sites in North America and 16,524 sites in Europe between 1996 and 2018. The team then used data and recordings from an online database of 1067 bird species to reconstruct the likely bird soundscapes that existed at each site during eachyear.
The team randomly inserted 25-second clips of each bird sighted at a location during a given year into a blank 5-minute sound file. Individual bird volumes were also randomly sampled to represent birds singing from a variety of distances.
"Ideally, it should sound like you've taken a recorder into the field with the individual conducting the bird survey," Butler explains.
The researchers then analyzed the clips using acoustic modeling, which quantified the acoustic characteristics of songs, such as volume and pitch, as well as their degree of variation. They found a significant decline in the diversity and intensity of bird songs on both continents over the past 25 years, implying that the soundscapes of these regions have become moresilent and less varied. The findings are consistent with the widespread decline in bird populations and biodiversity in North America and Europe during the same time period.
Large increases in human activity, such as agricultural intensification, poor forest management, pollution and urbanisation, contribute to these declines. Butler adds that climate change has also impacted the distribution of birds in the UK.
Because birds are used as a proxy for the health of biodiversity in general, declining bird populations indicate that other groups, such as amphibians and insects, may also be declining.
According to Butler, "Time spent in nature provides numerous physical and mental benefits to one's well-being and health. If the quality of these experiences is deteriorating as a result of changing soundscapes, it implies that the value and benefits of spending time outside are also deteriorating."
