Digital ears in the rainforest: Estimating dynamics of animal populations by using sound recordings and computing

The canopy in a Brazilian rainforest is bustling with life, but nothing is visible from the ground level. The digital recorders attached to the trees, however, are picking up the noises of birds.

"We can assess the factors which impact the distribution of bird species based on these recordings. If we can hear the song of a certain species in our recordings, that means at least one individual was present. If the song is not on the recording, either no individuals were present or they were not singing. However, just knowing whether a bird was there or not tells us little about the size or structure of the population or the movements of individual birds, so this is just the starting point," explains Ulisses Camargo, who is currently working on his dissertation at the Faculty of Biological and Environmental Sciences at the University of Helsinki, Finland.

The newly launched Finnish-Brazilian project seeks to glean more information from the massive amount of recorded data using statistical methods and scientific computing.

"Our first objective is to create an algorithm that can automatically sift through tens of thousands of hours of recorded material. The algorithm should be able to identify the species of birds by their song and indicate how reliable this recognition is. After that, we will use our network of digital recorders to determine which factors impact the population fluctuations of species and communities. We will examine how the animal communities in natural and disturbed forests differ from one another, or how the proximity of a river influences the population density of different species," describes Professor Otso Ovaskainen.

Professor Ovaskainen's group has already begun the development of the software to be used for species identification, building on existing molecular species identification algorithms based on DNA sequencing. The intention is to construct the software so that it can later be used on other animals identifiable by the sounds they make, such as frogs.

In addition to the network of digital sound recorders, the Brazilian partners in the study use several other technologies, such as small GPS transmitters which allow them to track the movements of large birds and mammals. A harmonic radar is used to monitor the movements of smaller organisms, such as bees. Thus, the overall objective of the project is to develop and combine new methods of field research and statistical modelling that will allow improved mapping and monitoring of tropical diversity.

The project is mainly financed by the Academy of Finland and FAPESP in Brazil.