Once a common feature of forests in North America from Southwestern British Columbia to San Francisco Bay, the Northern Spotted Owl's population has been in steady decline since the 1980s.
Fast-tracking this plunge was a fierce competitor from the East, the Barred Owl, which quickly began displacing the Northern Spotted owl at a time when they were already being threatened with increasing habitat loss. Though they look very similar to Spotted Owls, Barred Owls are larger, more aggressive, and are less picky about what they eat- making them more adaptable. Today, the Barred owl occupies the entire range of the Northern Spotted Owl, and they have nearly eclipsed their smaller counterparts.
With just an estimated 1,200 pairs now left in Oregon, the need to locate Spotted owls is both more difficult and more necessary than ever. But the tactic used for the last 50 years to find them may also have been putting them in more jeopardy. In the past, scientists were successfully employing a call-and-response method to locate the Spotted owls. Unfortunately, when the owls hooted their responses, they were also giving away their location to Barred owls nearby.
To keep their coordinates undercover, scientists like Damon Lesmeister of Oregon State the United States Forest Service switched to a stealthier method-- acoustic monitoring. At each site, Damon and his team set Song Meter SM4 audio recorders on trees and scheduled them to record for a few hours around dawn and dusk, when the owls were most likely to call. Lesmeister now has an army of over 500 recorders listening in Oregon. If an owl hoots, you can bet he will hear it.
With that much data, though, researchers can’t simply sit down and listen to what amounts to millions of hours of audio. At Oregon state, they have supercomputers and custom AI programs searching through the massive volumes of forest sounds. Others use analysis software like Kaleidoscope Pro, which intelligently scans the recordings for sounds of interest (in this case owl calls) and groups them neatly into clusters. The researcher can then tab through each sound bite that the software thinks is an owl and can make the decision – owl, or not an owl?
Lesmeister and others in the field hope that the recordings they gather now will serve as baseline data to understand a changing world. As time goes on, he believes that acoustic monitoring will become the standard for listening to the disappearing birds, and hopefully find the answers needed to bring their numbers back up.
To learn more about Damon Lesmeister's research and hear Northern Spotted Owl calls, visit his website here.