Utilizando Características Acústicas e Fisiológicas para Abordagens Ecológicas das Aves em uma Paisagem Fragmentada na Amazônia Central

Abstract

In Amazon, the construction of hydroelectric dams is a growing factor in the biodiversity loss. In such environments, fragments acts as true islands, presenting low species richness on small islands. Consequently, tools that can monitor changes in communities are becoming increasingly important. In the first chapter, we evaluated the performance of seven acoustic indices (biodiversity indices based on the soundscapes analysis) in forest islands within an anthropogenic archipelago of central Amazonia, to address the following questions: (1) is there a relationship between bird richness and acoustic indices? (2) what is the relationship between soundscape patterns and landscape features such as island size? (3) how do soundscapes change throughout the day in islands of different sizes? and finally; (4) how do birds and cicadas use their acoustic space on islands of different sizes? In fragmented environments it is also necessary uncover the physiological mechanisms underlying the success of organisms living in disturbed habitats. In the second chapter, we use the corticosterone levels present in bird feathers as a measure of physiological stress, assessing whether corticosterone levels reflect the effects of landscape fragmentation related to the island size. For the first chapter, 12 islands and two areas of continuous forest were sampled. Using two autonomous recorders per area, one-minute recordings were made at five-minute intervals, for 24 hours, for three consecutive days. The acoustic indices exhibited different patterns, with marked changes between day and night. Our results show that five indices (acoustic complexity, acoustic diversity, acoustic entropy, median of the amplitude envelope and spectral flatness) reflect the species richness in each area. When we correlate the acoustic indices with island size, only the acoustic entropy index had significant results, presenting higher values with increasing area size. For the second chapter, we captured birds in 13 islands of varying size and in two continuous forests and analysed feather corticosterone levels of 265 individuals from eight different species. Our findings did not support the hypothesis that corticosterone varies in relation to island size, except for Hypocnemis cantator, which presented the predicted pattern: decreasing feather corticosterone levels with increasing island size. Overall, we conclude that even in a highly diverse environment, such as tropical forests, acoustic indices provide an excellent complementary tool for biodiversity assessment when provided with a ground-truthed database. Further studies are necessary to assess the reliability of corticosterone levels as a physiological measurement of stress and to determine which parameters are useful to understand how insularization caused by human activities may influence the resistance of avian populations to habitat disturbances.