When we were stationed at the Cornell Lab of Ornithology in Ithaca, New York, the bioacoustic department developed something they called an “autonomous recording unit.” Everyone there called them ARUs. They were essentially a microphone (or microphones) that were connected to a simple, tiny computer and drive on to which sounds were recorded and saved based on schedules that were programmed into the computer. The bioacoustic division first developed these for use in recording whale sounds. Each unit was placed in a waterproof unit and dropped into the sea on an anchor line. Each ARU could be left for weeks or months, retrieved, brought back to the lab, and the sound files downloaded and analyzed.

When search began in the early 2000s in Louisiana and then later in Arkansas to look for hard evidence of the possible existence of the previously presumed extinct ivory-billed woodpecker, the Cornell Lab of Ornithology developed an ARU that could be deployed on land. They were custom-made units that were a bit large and unwieldy and were usually connected to a car battery so they could keep recording for months at a time. Many interesting sounds were recorded on these units including some occasional distant sounds that at first sounded like the distinctive double-knocks known of ivory-billed woodpeckers. Unfortunately all of these sounds were determined to be from other sources including from shotgun blasts and the sounds of trucks driving over wooden bridges.

Later the bioacoustics department at the Cornell Lab of Ornithology created more units that were eventually used to inventory and monitor African forest elephant populations in Central Africa for the Elephant Listening Project. Other researchers at Cornell developed entire arrays of microphones arranged in grids that could simultaneously monitor many vocalizing birds at once. These arrays use computer algorithms to determine the location of a singing bird within the grid of microphones and so can provide information about how each bird reacts acoustically and spatially to nearby birds.

Other labs around the world have developed their own versions of the ARU for use in various kinds of research and monitoring of animals that make sounds. In recent years a Massachusetts-based company called Wildlife Acoustics has been selling rugged, well-designed ARUs that can be used for detection and monitoring of birds, bats, frogs, whales, insects—really anything that produces sounds. We have had the opportunity to use one of their most popular ARU models called the Songmeter. The unit is about the size of a dictionary and comes with two built-in small weatherproof microphones. A multitude of sound recording schedules come pre-loaded or you can make your own. We like the pre-loaded schedule that has the unit record for an hour before and after dawn and dusk. The recordings are stored on the same little SD cards that are used in digital cameras. The SD cards can be pulled out of the Songmeter and plugged into your computer to download the files and listen to them.

We enjoyed setting up a Songmeter on the back lot of the family property in Edgecomb this spring. Even though we didn’t have the opportunity to spend loads of time roaming around ourselves, we had the pleasure of listening to the beautiful sounds of frogs and newly arriving birds. There is something amazing about hearing the sounds of the forest recorded when no human is anywhere around. On recordings made before dawn in late April we would hear the haunting flutey notes of hermit thrushes with a chorus of spring peepers in the background, the first awakening crows calling in the distance, the incredibly thin, high-pitched sounds of golden-crowned kinglets and brown creepers, and yes, even the sounds of early morning commuter traffic on Route 27.

You can enjoy these sounds yourself, as we have saved a file here: https://soundcloud.com/birdwells/early-morning-mixed-forest-bird-sounds-edgecomb-me-april23-2016-s4a01495mf9t-062202

Yet another cool technology tool to learn more about our natural world!    

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the book, “Maine’s Favorite Birds.”