Listening in on the forest: use of bioacoustics to preserve soundscapes and rare species

Effective monitoring and protection of tropical ecosystems has the potential to conserve vast amounts of the earth’s biodiversity. Yet logistical and technical challenges associated with species rarity, large distributions and home ranges, low detectability and inaccessibility of study sites can hinder monitoring efforts. If we are to mitigate against the threats to biodiversity and restore natural ecosystems, then we urgently need rapid and cost-effective methods to evaluate the current state of species, communities, ecosystems and the effectiveness of interventions. Here, we use passive acoustic monitoring (PAM) combined with computational approaches, as a method to effectively measure trends in biodiversity at a wide spatial scale across a biodiverse region in the tropics. In Chapter Two we used soundscape analysis to evaluate changes in acoustic diversity across the diel cycle over a gradient of land use change. We aimed to assess if soundscape indices can reveal changes in the biological community across the diel cycle and whether loss of native forests affect acoustic diversity in tropical ecosystems. In disturbed habitats, we found a loss of the characteristic dawn and dusk peaks in the diel cycle; known as the dawn and dusk chorus. This was especially prominent in palm oil plantations and grasslands, which showed a complete loss of these peaks. This suggests that in disturbed ecosystems there is likely a loss of species diversity, a shift in species composition, where forest specialists are being replaced by disturbance tolerant species, or that there are modifications in species behaviour, reinforcing the value of native old growth forests in maintaining ecosystem functionality. This loss in dawn and dusk peaks was not apparent when analysing acoustic diversity at specific times during the diel cycle, showing that evaluating acoustic diversity at this temporal scale can be misleading, but in assessing trends across the diel cycle, we can gain a much better representation of changes to biotic communities. In Chapter Three we determined if PAM and a newly developed automated detection and classification system was effective at retrieving information on the Geoffroy’s spider monkey at a wide spatial scale. We assessed how this endangered primate responds to habitat loss and human influence across a gradient of disturbance. We found that the Geoffroy’s spider monkey was absent below 80% forest cover and within 1 km of paved roads, yet was found to some extent in areas of secondary forest and near unpaved roads and buildings. The success of this methodology in the study of a vocal rare species suggests that similar rare species could be studied in the same way. Threshold values for percent forest cover and paved roads will be valuable in developing conservation strategies for the protection of this species. In Chapter Four, we investigated the effectiveness of a sustainable use forest reserve in facilitating connectivity for the Geoffroy’s Spider monkey between two National Parks. We specifically evaluated occurrence across the reserve, habitat suitability, barriers to connectivity and potential mitigation strategies to improve connectivity in the region. We found that the Golfo Dulce Forest Reserve is acting as a buffer to Corcovado National Park and is able to support populations of the Geoffroy’s spider monkey, however, as occurrence was limited to the area surrounding Corcovado, it is possible that it is not facilitating connectivity as intended. Primary road and low forest cover were the most important predictors of poor habitat suitability, both acting as barriers to connectivity and potentially impeding the conservation of an endangered species. This is problematic since Piedras Blancas National Park serves as a connection between the Osa Peninsula and populations of the Geoffroy’s spider monkey in other areas of Costa Rica. In summary, we have shown how PAM, combined with computational approaches, can be used to effectively monitor trends at both fine temporal scales and wide spatial scales across a tropical ecosystem. PAM has provided an effective and rapid approach to monitor trends in biological communities across disturbance gradients, to study rare species across a challenging environment and to evaluate the effectiveness of current management interventions, overcoming many of the key logistical and technical challenges associated with biodiversity monitoring. These methods have revealed important information regarding how anthropogenic disturbance, related to land use change and human development, are threatening both species and communities, which can contribute to setting targets and developing conservation strategies for the protection of biodiversity in the Osa region and beyond. Open Access