May 27, 2025Documenting wildlife in the field can be a slow endeavor.
Roaming through vast landscapes of often-times wildly overgrown and insect-filled habitat looking for individual birds, mammals, insects, and other hard-to-find wildlife can sometimes uncover very little, if any, evidence that they’re around. For River Partners’ biologists and ecologists, though, the reward for perseverance comes when they spot a rare or elusive species. It also proves that restored riparian habitats provide thriving homes for all kinds of wildlife, especially those on the brink.
Through our longstanding partnership with the California Department of Fish and Wildlife (CDFW), River Partners has been studying wildlife at numerous sites along the 3,900-acre Sacramento River Wildlife Area (SRWA)—through field monitoring, reviewing tens of thousands of camera-trap photos, and listening to more than 3,900 hours of audio recordings. Below, we’ve shared some highlights of what we discovered.
The SRWA, which extends through Colusa, Glenn, Tehama, and Butte counties along the Sacramento River, contains 13 different sites that are a mix of remnant forest, grasslands, and habitat that has been restored by various conservation agencies and organizations, including River Partners, for more than 20 years.
“The number and diversity of wildlife that has returned after restoration throughout the SRWA is nothing short of inspiring,” said CDFW Wildlife Area Coordinator Karen Converse. “The habitat along the Sacramento River is a vital corridor for wildlife, and as we continue to restore these sites, we’re seeing more and more wildlife thrive and make their homes here.”
Blending a century of wildlife investigations on the Sacramento River with modern monitoring technology and techniques, like installing cameras and autonomous recording units (ARUs), is giving conservationists a clearer picture of the wildlife that once thrived here, what disappeared, and what’s now returning.
“We know from past records that there are species that used to be here that are no longer here,” said River Partners Associate Director of Restoration Science Michael Rogner. “We put out cameras and ARUs to hopefully capture something that’s rare, but it’s also important to continue the science of documenting these species’ decline.”
This riparian ecosystem along the Sacramento River has revealed a handful of critical species that are using these sites after being absent for myriad reasons and returning to find new residences.
“This is our mission at River Partners and why we need to be doing continuous large-scale restoration along the river,” said River Partners Restoration Science Ecologist Dr. Sarah Gaffney. “It’s important for these species that we continue doing this.”
Below are some of the species—from endangered to elusive—that were detected during the study. These were found in a mix of restored, remnant, and grassland habitat, showing that the wildlife is there, and that it is of critical importance to continue restoration efforts on degraded lands.
Birds
CDFW selected three focal species it was most interested in detecting: the yellow warbler, yellow-breasted chat, and yellow-billed cuckoo. The recordings below are what our ARUs picked up between April 23 through August 1 last year. Our technology partner Conservation Metrics custom built an avian detection and classification model tailored specifically to pick up and identify these species of interest.
Yellow Warbler
Yellow warblers are common throughout North America—except along the Sacramento River due to habitat loss and nest parasitism by brown-headed cowbirds. So, when this at-risk species’ calls were recorded at the Beehive Bend Unit in Glenn County and the Colusa Unit in Colusa County, we took note. Vocal detections happened throughout the morning and peaked within the first 20 minutes after sunrise. It’s common to see yellow warblers flitting through the cottonwoods during migration, but the timing of these detections indicated they were attempting to nest along the river, which is rare.
Yellow-Breasted Chat
The yellow-breasted chat has a large territory and can be loud, so if it were around, the ARUs would pick it up. That’s exactly what happened at one plot at the Ord Bend unit in Glenn County and two plots at the Colusa Unit. The bird (categorized as a species of concern) was particularly busy at the Colusa Unit. It was recorded sporadically throughout the morning, starting just before sunrise and then nearly every day from June 20 to August 1 at a single plot at Colusa Unit. This activity indicates territorial, breeding behavior. A fire burned through the Colusa Unit in 2022, and the thick understory which returned makes the habitat ideal for the chat. With tall trees and open sight lines thanks to the fire and dense ground cover consisting of wild grape and blackberry, it’s no surprise the yellow-breasted chat was detected here.
Yellow-Billed Cuckoo
The rarest bird encounter along the Sacramento River was the yellow-billed cuckoo. A solitary call of this endangered bird was detected at a plot at Ord Bend—it’s likely this single bird was prospecting for other cuckoos with which to breed. Habitat loss and fragmentation, as well as the disappearance of their prey base due to pesticides, have contributed to plummeting numbers of this species along the Sacramento River. With a patchwork of restored and unrestored habitat along the Sacramento River, it’s imperative that future restoration efforts work strategically to connect with previously restored riparian habitats so that wildlife here can expand their territories to begin thriving once again.
“Finding a yellow-billed cuckoo on the Sacramento River is like finding a needle in a haystack,” Rogner said. “I think that was the only detection of a yellow-billed cuckoo all of last year. Even their last stronghold along lower Butte Creek was silent.”
Crotch’s Bumble Bee
River Partners Restoration Biologist Kim Armstrong saw two of these endangered insects at Merrill’s Landing in Tehama County. Perhaps as important as finding the pair of bumble bees is where she found them—in an area adjacent to previously restored grassland habitat among blooming gumplant, lupine, and elderberry. Finding Crotch’s bumble bees so far north along the Sacramento River, particularly next to a previously restored grassland, shows the importance of restoring habitat for pollinators.
“The restored grassland isn’t just supporting the bumble bee, it’s supporting a whole host of other species,” Armstrong said. “Native grasslands are important for birds, used as cover for ground-nesting birds like sparrows and waterfowl. It’s not just habitat for one species, it’s habitat for a lot of the animals that rely on them.”
Ringtail
While not as rare, it is elusive, nocturnal, and quiet—and about as cute an animal as you’ll see. This photo of a ringtail, a species of special concern, was taken by a camera at the Colusa Unit. This smaller member of the raccoon family, can dwell among the foothills as well as along riparian zones. The Colusa Unit lies just north of a future River Partners restoration site, Colusa Bend.
“Right now, habitat along the Sacramento River resembles a mosaic with fragments here and there,” said River Partners Restoration Science Ecologist April Damanti. “We are working to reconnect fragmented habitat via restoration to give species a contiguous corridor to travel in this habitat.”
So Now What?
As Rogner puts it, it’s a nice story that these rare and elusive species were detected at restored riparian habitats, but what does it mean in the bigger conservation picture?
“We know it’s incumbent on River Partners and the other conservation organizations working in California,” Rogner said. “There’s no time to dilly dally around talking about this, we need action on the ground because species are going extinct.
“Documenting the science part of the restoration really helps tell the story to funders to make action happen.”
Lead photo courtesy of Creative Commons
