The accelerating pace of conversion of natural landscapes to human-dominated ecosystems requires us to consider new ways to explore and understand diversity in natural areas. One approach is to record soundscapes, which are the collective sounds of environments; that is, sounds generated by animals, geophysical processes such as wind and rain, and humans and their activities. Soundscapes reflect the distribution and diversity of vocal species over time and space, but with their diverse inputs, can also reveal the extent to which land-use change affects acoustic communities and ecological complexity. We explored the influences of land-use and anthropogenic noise as well as habitat, weather, and season, on acoustic diversity of nature preserves within the mixed-use land matrix of southwest Michigan, USA. We recorded soundscapes during the avian dawn chorus in forest and grassland habitats at nine nature preserves over four months. From recordings, we calculated the Acoustic Complexity Index (ACI), which has been shown to be a robust indicator of avian acoustic diversity. We analyzed patterns of ACI over time and space in relation to land-use, anthropogenic noise, habitat, date of sampling, and time of day using generalized additive models.
Results/Conclusions
Using data from more than 180 h of recordings, we found that acoustic complexity was higher in grassland than forest habitats and that ACI changed over the season in both habitats, but in different ways. ACI was generally higher in grasslands than forest. Whereas ACI in forests generally peaked early in the breeding season, ACI remained relatively steady across the season at most grassland sites. In terms of time of day, ACI peaked shortly after sunrise in grasslands, but in forests complexity increased only slightly from 1 hr before to 3 hr after sunrise. Analysis to date revealed significant effects of date, time, and habitat in a generalized additive model that explained ~ 20% of the variation in ACI. Sound pressure levels in frequency bands characteristic of anthropogenic noise varied across sites, but preliminary analysis suggest limited effect of noise on ACI. We will present final model results incorporating land-use, anthropogenic noise and weather in addition to those variables already considered to more fully understand patterns and drivers of acoustic diversity during the dawn chorus.