A study by the University of the Americas (Universidad de la Américas Puebla) and the Basque Institute for Agricultural Research and Development (Neiker-Tecnalia) reveals that noise pollution has negative effects on songbirds in cities. The fieldwork, carried out in urban parks in the Metropolitan Area of Puebla-Cholula (Mexico), shows that the green zones most affected by noise have fewer bird species within them. Among species better adapted to urban conditions are various finches, sparrows and thrushes. The authors of the study say that noise is a novel environmental factor to be taken into consideration when analysing urban biodiversity.
Urban park, Bravo Avenue, Puebla-Cholula (Elhuyar Fundazioa).
The conclusions of the study, recently published in the scientific journal Landscape and Urban Planning, can be extrapolated and applied to other cities with similar characteristics. The green spaces studied included urban parks, main squares, university campuses, natural reserves close to the city, and cemeteries. The study examined the frequency of occurrence of 38 songbirds (generally small birds such as sparrows, blackbirds, swallows, larks, thrushes, etc.). Urban park noise levels ranged between 62 and 72 decibels (dB), main squares between 54.5 and 62 dB, and university campuses between 53 and 58.5 dB. The lowest average noise levels (of 38.4 dB) were recorded in protected natural areas. The two cemeteries included in the study were also quiet places, revealing an average of 45 dB.
Squares and urban parks, the noisiest sites studied, had the smallest number of species. On the other hand, sites with the highest number of species were the natural reserves and university campuses. The songbirds best adapted to the noisy urban conditions were House Finch, House Sparrow and Great-tailed Grackle, which were observed in all the green zones studied. Species such as Rufous-bellied Thrush, Bewick's Wren and Curve-billed Thrasher also tolerated the noisier areas but others such as White-collared Seedeater, Scott's Oriole and Rose-breasted Grosbeak had a decreased presence in the noisier metropolitan areas.
That noise pollution influences bird diversity in urban ecosystems is a new finding, and Neiker-Tecnalia is keen to be at the forefront of research in this field. The researchers conclude that noise pollution has a negative effect on birds, and recommend additional studies to expand the incipient knowledge gained from this study. The next scientific challenge is to find out what levels of noise can be tolerated by all bird species that inhabit urban environments.
To ensure that birds can co-habit cities with humans, Neiker-Tecnalia proposes that green zones should increase the size of wooded areas; foliage acts as an acoustic screen and reduces noise from traffic and other human activity such as construction work and aviation.