The soundtrack of the birds, more simple and monotone


The population of many bird species has declined in recent decades and with it their contribution to nature’s increasingly seamless and silent soundtrack.

The trill of birds and natural sounds facilitate physiological mechanisms that improve our organism, promote our physical health and our psychological well-being. It does us good to listen to nature. If the soundtrack of the birds continues to deteriorate, the silence of the birds will eventually affect the health of human beings. The recordings we have made already show its decline.

In silent springRachel Carson explains how the sounds of nature have been intimately linked to the perception of the quality of the environment and anticipates a future in which birds will have stopped singing:

“It was a speechless source. The mornings that once beat with the chorus of robins, doves, jays, wrens and dozens of bird calls, now there was no sound; only silence stretched over the fields, forests and swamps… Even the streams were now lifeless… No sorcery, no enemy action had silenced the rebirth of new life in this ravaged world. People had done it for themselves.”.


The integrity of the natural soundscape is increasingly integrated into conservation and environmental health policies and actions. In an urban and sedentary society surrounded by barriers of access to the natural environment, it is increasingly difficult to feel natural stimuli, such as the chirping of birds, which have informed and accompanied us during most of our journey. as a species.

In recent research published in Nature Communicationwe’ve studied how the soundscape has changed over the past 25 years in over 200,000 locations in North America and Europe, and found that it’s getting simpler and more monotonous.

From CREAF and ICO, we worked within an international team of researchers, led by Simon Butler, from the University of East Anglia (Great Britain). The basis of the work was to reconstruct for the first time on a large scale the acoustic structure of the soundtrack of birds at different times and places.

To achieve this, we combined bird count information obtained from millions of citizen science observations, coordinated on a continental scale, with records of individual species outdoors.

Reconstructing soundscapes

To reconstruct bird soundtracks over time, historical soundscapes, we rely on extremely rich databases through citizen science: North American Breeding Bird Survey and the Common pan-European bird monitoring program. In addition, we had the recordings in the natural environment of more than 1,000 species of Xeno-Song, an exhaustive database of free access with the trill of songs and calls of birds from all over the world.

Thanks to these rigorous databases, we can know with great precision which species of birds and how many individuals of each species were in a specific place at a given time. With this information, we can create the soundscape of that place, at that time, combining in the proportion indicated by the census the recordings made outside of the individuals of each species represented. We assigned a five-minute file to each soundscape and a 25-second file to each individual of a species.

25 years of bird sound recordings

Once the soundscapes of each place were created and at different times over 25 years, we established four indices that allowed us to quantify their richness. The acoustic cues we have established are related to the variety and abundance of bird species and the complexity of their songs.

Our analysis is based on “heard” changes at each site over the years, independent of ongoing environmental changes. This allows works like this to show us unequivocally how the world around us is changing.

Loss of biodiversity and bandwidth

The results of the study reveal a chronic deterioration in the quality of nature’s soundtrack in North America and Europe over the past decades. The global loss of biodiversity is one of the realities that best explains it. We have identified the places where the diversity and acoustic intensity of its soundtrack have decreased the most, and they correspond to environments where there is less abundance and richness of species.

However, the damping of birdsong has nuances, for example, it influences the type of species involved and their numerical evolution in the environment.

For example, the loss of a species like the Song Warbler, which sings a rich and complex song, is likely to have a greater impact on the complexity of the soundscape than the loss of a species of corvid or gull, which are always more monotonous and harsh. So how this affects the nature soundtrack will also depend on how many musical warblers are present in the location and what other species share that corner of the world.


This study focuses exclusively on birds, however, reducing other biological groups also most likely impoverishes the nature soundtrack.

Add to the deterioration the steady and widespread increase in human-generated noise and other sensory pollutants, which serve as a screen for natural sound. Different studies show that birds are forced to reduce their song when human activity intensifies. The confinement caused by covid-19 was a small opportunity to verify that, when our activity decreases, urban birds sing again, as if the absence of humans implied a more natural environment.

Character font: Sergi Herrando Vila / Lluís Brotons / THE CONVERSATION

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