Goodbye birds…?

The Eurasian Skylark (Alauda arvensis) is an example of a bird with a rich song whose population is declining. Photo: Jan Grünwald.

Despite all the advances taking place in science, the modern world with its increase in electronic media gives us fewer and fewer opportunities to connect with nature and thus stay healthy, both physically and mentally. The claim that nature can heal us is not said in vain. The COVID-19 pandemic, along with its restrictions and lockdowns, has highlighted even more how vital the surrounding natural world is to us.

There is no doubting the importance of diversity and the number of birds in our landscape. As an example, we can cite recent problems with the overpopulation of voles in our territory, which is partly caused by the lack of predators who are losing their homes as a result of urban pressure. One of the major contributors to natural soundscapes are birds and bird song, which is also one of the indicators of the quality of our contact with nature. Extensive reductions in both species richness and bird abundance will affect the acoustic properties of natural soundscapes and reduce the quality of such experiences.

The researchers combined data comprising the recordings of individual bird species at more than 200,000 locations across North America and Europe over the past 25 years. They reconstructed the soundscapes for each location for every one of those years. The acoustic characteristics were then quantified using four indices. These indices were designed to capture the distribution of acoustic energy across frequencies and time and to reflect the richness (Acoustic Diversity Index: ADI), evenness (Acoustic Evenness Index: AEI), amplitude, (Bioacoustic Index: BI) and heterogeneity (Acoustic Entropy: H) of each soundscape.

Using the above-mentioned indices, it was possible to assess the perception of the quality of natural experiences by the public, while lower values of ADI, BI and H, and higher values of AEI reflected a reduction in acoustic diversity and intensity.

Since the late 1990s, there has been an almost identical decline in the ADI, BI and H indices on both continents and a significant increase in AEI in North America over the same period. However, it was also possible to monitor certain local variations. For example, the decrease in acoustic diversity (signalled by decreases in ADI and increases in AEI) have been greatest in the north and west of both continents, while soundscape intensity (measured by BI) has declined most in the more northern and eastern areas of North America. Overall, however, the soundscape has become much quieter and more homogeneous.

This unique study of bird songs across North America and Europe has yielded worrying results. The authors have raised the alarm. Sound is a defining feature of our contact with nature. When its quality decreases, the connection between humans and nature also decreases. This may further contribute to the global environmental crisis, as there is evidence such cases may lead to a reduction in pro-environmental behaviour and consequent environmental degradation. It is therefore necessary to focus not only on the conservation and restoration of natural bird habitats, such as nature parks and forests, but also country lanes and gardens. Reducing the fragmentation of the bird landscape, primarily caused by large fields, is also important. This will not only benefit the birds but also bring us a happier life and good health.

Kateřina Fraindová

Morrison CA, Auniņš A, Benkő Z, Brotons L, Chodkiewicz T, Chylarecki P, Escandell V, Eskildsen DP, Gamero A, Herrando S, Jiguet F, Kålås JA, Kamp J, Klvaňová A, Kmecl P, Lehikoinen A, Lindström Å, Moshøj C, Noble DG, Øien IJ, Paquet JY, Reif J, Sattler T, Seaman BS, Teufelbauer N, Trautmann S, van Turnhout CAM, Vořišek P, Butler SJ. 2021, Bird population declines and species turnover are changing the acoustic properties of spring soundscapes. Nat Commun.12(1):6217. doi: 10.1038/s41467-021-26488-1.