Bioacústica como ferramenta para estudo da influência do ruído antrópico nas aves

Abstract

Urbanization cause changes in the landscape and represents an important threat to biodiversity. High noise levels lead to diminishing diversity, richness and reproductive success of birds, pose challenges for birds communication during social interactions, mainly to attract a female during reproduction and in the defense of the territory, and cause changes in the bird vocalization patterns and soundscape composition. The objectives were to calculate the environmental noise levels, to describe the composition of the soundscape and to calculate the acoustic diversity verifying if they vary between groups of areas and if they are related to the environmental noise. To verify if bird richness vary and what characteristics of forest areas (size and distance to cities and highways) best explain the variation in the richness of bird species in these environments. To calculate six acoustic indices [Acoustic Complexity Index (ACI), Acoustic Diversity Index (ADI), Acoustic Evenness Index (AEI), Bioacoustic Index (BIO), Acoustic Entropy Index or Total Entropy (H), Normalized Difference Soundscape Index (NDSI)] and verify if they are related to vocalizing species richness and noise levels. To verify which species present variations in the song parameters and which parameter presents greater sensitivity to the effects of environmental noise. The areas were grouped into rural, semi-rural, semi-urban and urban areas. We made recordings between March / 2015 and February / 2018 with Marantz PMD 661 Mark II digital recorder and Sennheiser ME67-K6 directional microphone. The environmental noise level was measured with a Sound Pressure Level meter. The environmental noise level was higher in urban areas and lower in rural areas. The acoustic landscape of the areas consists mainly of sounds of birds, insects and vehicular traffic. The distance to cities was the most related factor to the variation in the biophony and the noise level was the one that was better associated with the anthrophony. Rural areas present higher biophony and urban areas greater anthrophony. The average richness of species recorded per stretch was higher in rural areas and lower in semi-rural areas. The richness of recorded birds is negatively related to environmental noise levels and positively related to the size of areas. The recorded richness of birds per area was higher in rural areas and lower in urban areas. The six Acoustic Indexes analyzed varied between the areas and between the groups of areas. The richness of birds per recording segment is related to ADI, AEI, H, BIO and NDSI, but is not related to ACI. Only NDSI is related to environmental noise levels and only BIO is related to the total richness of birds. Forty-one species of birds showed variations in corner parameters. In areas with higher noise levels, 26 species had a higher minimum frequency, 18 had a higher maximum frequency, 13 had a lower frequency range, 14 had a higher dominant frequency, 22 had greater song amplitude, and 09 had shorter song length. The distance to cities and environmental noise levels are the main factors associated with variations in anthrophony and biophony. BIO is the index that best reflects the richness of recorded bird species and NDSI the best to evaluate human impacts. The parameter minimum frequency was the one that presented greater sensitivity to the changes in the environmental noise levels.