The new field of soundscape ecology seeks to study how the sound diversity varies in the landscape, the soundscape. This soundscape can be another resource that species must deal with. In addition, the soundscape can be used as a monitoring tool for a diversity of animal groups like mammals, birds, anurans, cicadas, and crickets. We measured the temporal and spatial patterns of the soundscape at a temperate site and we wanted to determine if the same patterns would emerge in a tropical rainforest. In addition, we wanted to see how much of the variation was explained by the forest type and location in a vertical profile.
We used automated digital recorders to sample the soundscape at La Selva Biological Station in Costa Rica. We sampled sites in both primary and secondary forests to test the hypothesis that the soundscape will be different between these forest types due to their different structure and animal communities. In addition, we measured the soundscape at three heights: near the ground, midstory, and above the canopy. We saved 5-minute stereo recordings every 15 minutes during 2 months. We extracted an acoustic diversity index from each file to quantify the sound diversity recorded at each sample.
Results/Conclusions
When we explored the sound diversity at each site, we found two daily peaks, one during the early morning and the other during the late afternoon. The period with the lowest sound diversity coincided with the hottest period of the day, between 1000h and 1500h. These results are similar to findings in temperate forests, which indicate that natural soundscapes may all have a similar pattern.
Sound diversity in the vertical profile exhibited a different patter at each height. The largest difference was between a height above the forest canopy, where the sound diversity was very low, and the other locations inside the forest. This difference was probably related to the temperature effects on the air column.
Our results have important implications for acoustic monitoring. While sound propagation is known to differ along the vertical profile, this study included the soundscape during day and night. If there is a target species or taxa, the recorders must be placed at an appropriate height according to the habitat use of the species. Just placing the recorders at a convenient heights for researchers will miss some data and will not capture the whole variation in the soundscape.