Ecologists are using a network of "outdoor recording studios" to better monitor the subtropical Japanese island of Okinawa. Now a pilot study, in which more than 1,100 hours of birdsong were analyzed, is available in the journal Ecological Research which is the official journal of the Ecological Society of Japan and is published by Springer.

The research was led by both Nick Friedman of the Okinawa Institute of Science and Technology in Japan, and Samuel Ross of the University of Leeds in the UK. The soundscapes they analyzed reflect how human activity influences the occurrence of species such as the Okinawa Rail and Ruddy Kingfisher on the island.

In this acoustic monitoring study, five pilot recording sites were set up in three city parks, a forest and a forested suburb on Okinawa, which is the largest and most inhabited island in the Ryūkyū archipelago. Together with nineteen other sites, these are part of the Okinawa Environmental Observation Network Churamori Project which monitors the island's plants and animals -- many of which are either endemic or threatened.

Indices from the recordings were calculated to reflect aspects such as the composition and complexity of the soundscape. The range of frequencies of the bird song were monitored as well as different sound intensities within a recording, as an indication of the diversity of birds present in an area.

The presence of five different bird species were also automatically detected using machine learning methods. The Okinawa Rail and Ruddy Kingfisher were, for example, most often heard in forested areas. This reflects the impact that urban development is having on the location of endemic species.

The research team recorded the influence that rainy weather and seasonal changes have on birdsong and the soundscape in general. They also learned when to start listening for different bird species. The Ruddy Kingfisher's song is, for instance, almost exclusively heard during the morning, while the Jungle Crow is audible throughout the day. The Okinawa Rail is the most silent.

The use of automated recording sites now makes it possible to monitor many field sites simultaneously, without the need for a large research team. Also, acoustic recordings do not interfere with the normal behavior of the animals being monitored. Thanks to technological advances in the development of miniaturized recording and data storage equipment, ecologists are now better able to analyze the sounds of nature and to monitor and measure the species living in a specific area.

"Our results highlight the potential use of remote acoustic monitoring practices that, in combination with other methods, can provide a holistic picture of biodiversity," says Ross. "We intend this project as an open resource, and wish to extend an invitation to researchers interested in scientific collaboration."