Baixo Sabor: Acoustic Bat Monitoring – Construction and Reservoir Filling Phases [2008-2014]

Sampling was designed to cover the dominant habitats occurring in the study area and that are normally used by foraging bats. A total of 97 sampling points was surveyed, stratified by habitat, considering the main habitat types represented in the region. Of these, 50 sites were located within the area flooded by the reservoir, 26 in areas above or around it, but outside its range of influence (2-5 km), and 21close to extant and future weirs in the tributaries of the River Sabor (above the flooded area). Each sampling site was visited once or twice per season, considering three seasons: spring (April-May), reproduction (July-August) and post-breeding (September-October). Sampling was carried out when there were favourable weather conditions, including temperature above 10º and absence of strong winds and rainfall. Acoustic sampling started at sunset and ended 2-3 hours later. Each site was sampled for 10 minutes.
The detection of specimens in flight was made with a bat detector (Pettersson Elektronik, D240X model), with a frequency range of 10-120 kHz. The detector was connected to an automatic digital recorder (model Sony ICD-PX312) which saved the recordings in a “Wave” format, at a frequency of 44 kHz and at an expanded mode of 10x, making them audible to the human ears while, at the same time, preserving the original acoustic characteristics.
The analysis of the acoustic records were performed using the sound analysis program BatSound Pro (Pettersson Elektronik AB). This program generates graphs (oscillogram, sonogram and power spectra) using the various sound variables that allow the identification of species or complexes of species detected.
The exact identification of the bat species by sound analysis is not always possible, due to problems in detectability and/or identifiability. In the context of this work, whenever it was not possible to perform the identification to the species level , the binomials, multinomials or genera to which the identification was possible were considered to be present. Thus, the presence of all species constituting these phonic groups (or “species complexes”) was considered possible.