Spring Soundscapes Are Changing as Bird Populations Continue to Decline - Smithsonian

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An image of a male Indigo Bunting sitting on a tree branch. The bird has vibrant blue plummage. — Unique trills, calls, chirps, gurgling, and whistles are crucial components in nature's soundscapes. (Pictured: Male Indigo Bunting) Dawn Scranton via Wikimedia Commons under CC BY 2.0

"It was a spring without voices. On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices, there was now no sound; only silence lay over the fields and woods and marsh," Rachel Carson wrote in 1962 in her ground-breaking book, Silent Spring.

Nature's sounds, especially bird songs, play a crucial role in building and maintaining human connections with nature. However, declining bird populations means fewer chirps are being heard, amplifying the human-nature disconnect. Now, a new study shows a "silent spring" may soon become reality.

Researchers examined bird songs and citizen science data from the last 25 years and found that the diversity and intensity of nature's acoustics are being silenced. The findings were published this month in Nature Communications.

"Bird song plays an important role in defining the quality of nature experiences but widespread declines in bird populations and shifts in species distributions in response to climate change, mean that the acoustic properties of natural soundscapes are likely to be changing," Simon Butler, an ecologist at the University of East Anglia, and one of the study's authors, told the Independent's Harry Cockburn.

Unique trills, calls, chirps, gurgling, and whistles are crucial components in nature's soundscapes. Previous studies have shown nature sounds connect people to nature, improve health, lower stress, decrease pain, and enhance cognitive performance.

To see how soundscapes have changed over the years, the research team compiled data from citizen science bird monitoring from 202,737 sites in North America and more than 16,524 sites in Europe taken between 1996 and 2018, reports Chen Ly for New Scientist. The researchers also took data and bird song recordings of 1,067 bird species from an online database called Xeno Canto to reconstruct what the soundscape may have been like at every site for each year over the past 25 years, the Independent reports.

To recreate these soundscapes, scientists inserted 25-second clips of individual bird songs reported in the citizen science data from a specific year into empty five-minute sound files, per New Scientist. To represent birds singing at varying distances, the team added depth and randomly sampled the volume of individual bird songs. Then, they analyzed the clips with an acoustic modeling program and paid particular attention to the song's volume, pitch, and variation.

After analyzing and compiling the data, researchers found a decline in diversity and intensity of birdsong in both continents in the past 25 years, meaning that the soundscapes have gone quieter with less variety in songs. The findings align with dwindling bird populations and diversity in Europe and North America, reports New Scientist.

"Time in nature has a lot of physical and mental benefits to well-being and health," says Butler to New Scientist. "If the quality of those experiences is declining because our soundscapes are changing, then that suggests the value and the benefits we get from spending time out there might also be deteriorating."

Agricultural intensification, pollution, habitat destruction, insecticides, urbanization, and climate change are all driving declines in bird populations, New Scientist reports.

Since the 1970s, 2.9 billion birds have been lost in North America alone, or 29 percent of the total population. Birdlife International also released a study last month that stated one-in-five bird species in Europe is threatened or near threatened by extinction. The study also revealed that one-in-three bird species in Europe has declined in the past few decades, the Independent reports.

"Unfortunately, we are living through a global environmental crisis, and we now know that the diminishing connection between people and nature may be contributing to this," the study's first author Catriona Morrison, a biologist at the University of East Anglia, tells the Independent.