A study by the University of the Americas (Universidad de la Américas Puebla) in Mexico and the Basque Institute for Agricultural Research and Development, Neiker-Tecnalia, highlights the fact that noise pollution has negative effects on songbirds in cities. The field work, carried out in urban parks in the Metropolitan Area of Puebla-Cholula (Mexico), reveals that the green zones most affected by noise have less bird species. Among the birds better adapted to urban conditions are various species of 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.
Specialists from the R+D centre point out that the conclusions drawn from the study –a piece of work conducted in the Metropolitan Area of Puebla-Cholula (Mexico) and which has been recently published in the scientific journal Landscape and Urban Planning– can be extrapolated to other cities of similar characteristics. The green spaces studied included urban parks, main squares, university campuses, natural reserves close to the capital city, and even cemeteries. The study examined the frequency of occurrence of 38 songbirds species (generally small birds, like sparrows, blackbirds, swallows, larks, thrushes, etc.).
The urban parks had average noise levels ranging between 62 and 72 decibels (dB); squares, between 54.5 and 62 dB, and university campuses, between 53 and 58.5 dB. The lowest average levels were recorded in a protected natural area, where the measurement was 38.4 dB. The two cemeteries included in the study were quiet places as well, with an average of 45 dB.
The results highlight the fact that squares and urban parks were the noisiest sites among those studied and, in turn, the ones with a small number of species, apart from other differences. On the other hand, the sites with the highest number of species were the large natural zones and university campuses. The songbirds best adapted to the noisy urban conditions were the 'house finch' (Carpodacus mexicanus), the 'house sparrow' (Passer domesticus) and the 'great-tailed grackle' (Quiscalus mexicanus), which were observed in all the green zones studied. Birds like the 'Rufous-bellied thrush blackbird', the 'Bewick's wren' or the 'Curve-billed thrasher' likewise put up with the noisy reality of the study area. In the green metropolitan areas other birds, like the 'White-collared seedeater', the 'Scott's Oriole', or the 'Rose-breasted grosbeak' had a lower presence.
Alongside other environmental variables, noise pollution is a new environmental factor that influences bird diversity in novel, urban ecosystems, and Neiker-Tecnalia has been keen to take an initial step in this matter. Its specialists report that noise pollution has a negative effect on birds, and they propose that additional studies be carried out to expand on the incipient knowledge in this field. Experts are of the opinion that the next scientific challenge is to find out what levels of noise can be tolerated by each of the species of birds inhabiting urban environments.
So that these birds can survive together with people in cities, apart from limiting the noise levels permitted in urban environments, Neiker-Tecnalia is proposing that these green zones should have more wooded areas. The foliage of the trees can act as an acoustic screen to cut the noise produced by road traffic –one of the main sources of noise in the city– or by any other human activity, like construction work or air traffic.