Photo: Oregon Department of Forestry

Oregon’s state forests are home to a wide variety of wildlife including two threatened bird species, the northern spotted owl and the marbled murrelet. As part of the Oregon Department of Forestry’s (ODF) compliance with the federal and state endangered species acts, ODF surveys where these species are and develops a plan to protect and enhance their habitat.

“Right now, we use call-back surveys to determine where spotted owls are,” said Mike Davis, an ODF state forest biologist. “As the name implies, we go out in the forest and broadcast owl calls and wait for them to respond, following a protocol accepted by the U.S. Fish and Wildlife Service (USFWS).” The USFWS administers the Endangered Species Act and monitors compliance with it.

Most of the field call-back survey work is done by contract biologists and has some limitations.

“For owls, the surveys are conducted at night and typically for just that one night at each location,” said Davis. “There are safety concerns too: driving dark gravel forest roads, hiking into the mature forest stands where owls typically are without any trails, and traversing steep, rugged terrain. Then standing or hiking for hours, oftentimes in the rain. It is not easy work nor a fun experience some nights.”

Another recent concern that limits the effectiveness of call-back surveys is the encroachment of the invasive barred owl into traditional spotted owl areas.

“The barred owls are basically bullying the northern spotted owls out of their preferred habitat,” said Davis. “We are seeing spotted owls at atypical higher elevations now and calling back less and less because that call alerts barred owls to their location.”

This makes the call-back protocols less effective and had ODF looking for better methods to survey the birds.

“In 2022 we started experimenting with Autonomous Recording Units (ARUs),” said Davis.

ARUs are devices that automatically record environmental sounds such as bird calls, frog choruses, or other wildlife vocalizations over extended periods without the need to have a human present.

“ARUs have many advantages,” said Davis. “They can be left out in the field several weeks or more, set up and retrieved from the field anytime, record multiple species, and can be analyzed back in the office.”

The units are designed similar to a trail camera, but instead of a camera they have a microphone. They also run on batteries and have removable memory cards.

“We bring the cards back to our office and run specialized software that processes the audio recordings,” said Davis. “It converts the sound waves into spectrograms, which are visual representations of frequency over time. Each species’ calls produce distinct patterns on these images, allowing software to identify and differentiate vocalizations.”

ODF is optimistic ARUs could save on survey costs too.

“We spend roughly $2 million a year on northern spotted owl surveys and another $500,000 on marbled murrelets,” said Corey Grinnell, Biological Support Unit Manager for ODF’s State Forest Division. “ARUs with rechargeable batteries, memory cards and the software costs are coming in the $600-$700 range per device.”

ODF currently has 23 ARUs but plans to deploy more and move away from sole reliance on call-back surveys.

“We are waiting for the USFWS to approve a final protocol for using ARUs,” said Grinnell. “Once that happens, we can integrate them more into our management plans.”

Another big change for the biologists will be state forests moving to a new Habitat Conservation Plan (HCP) that is expected to be approved by the USFWS and NOAA Fisheries later this year after a several years-long development and approval process. The HCP will give ODF 70 years of certainty in how ODF manages for 17 terrestrial and aquatic species, including northern spotted owls and marbled murrelets, as it manages state forests.

“The entire point of the HCP is to keep this working forest working,” said Grinnell.

The HCP combined with improving technology has the potential to give managers better data to better manage the forests. State forests by law must provide social, economic, and environmental benefits to Oregonians.

“Our goal is to create healthy productive forests, high-quality habitat for native fish and wildlife, clear cool water, benefits and revenues to rural communities and timber related economies, as well as recreation and educational opportunities,” said Grinnell. “To do that we embrace cutting edge technology to improve our data in the most cost-effective way. “ARUs are one tool to do that. We are always on the lookout for better, faster, cheaper ways to get biological data to help us make the best management decisions.”

Source: Oregon Department of Forestry

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