Science Spotlight

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  • June 24, 2020

small gray bird with black beak, wings and chest, yellow head with mouth open in a tree with branches and leaves
Hermit warblers spend much of their time in forest canopy. They are rarely seen but very vocal and easily heard. Photo by Dr. Brett Furnas.

's arm holding a recording device to record songs of small gray birds
Scientists record songs of hermit warblers and use the data for surveys that support conservation efforts. Photo by Russ Landers.

illustration of drawn trees with musical notes
Hermit warblers flee wildfires which ultimately creates opportunities for new birds to take over a habitat. This may explain why some areas have multiple mating dialects. Illustration by Sarah Noll..

New research shows that fire history seems to be shaping the diversity of bird songs throughout the state. The new paper, published in leading bird journal The Auk: Ornithological Advances, addresses the diversity of song dialects sung by hermit warblers – birds which get their name because they are rarely seen and spend much of their time in forest canopy. They are, however, very vocal and easily heard.

Interestingly, the paper’s lead author, CDFW Senior Environmental Scientist Dr. Brett Furnas, never set out to study the hermit warbler, which is a migratory songbird that breeds in California, Oregon and Washington.

Dr. Furnas’ journey studying the bird began a decade ago while he and his colleagues were doing surveys on songbirds in northern California. They noticed that songs from one species of songbird – the hermit warbler – were so complex that it was difficult to identify the species.

“We ultimately compiled a list of 35 different song dialects from the hermit warbler throughout California,” said Dr. Furnas

The team also noted, as had been confirmed in prior research, that all of the hermit warblers’ songs in a particular area sounded the same -- and they believed those songs to be the males’ mating calls.

“Females in that area were probably raised to recognize that one type of call. The males have to sing it perfectly,” said Dr. Furnas, noting that the birds do have a repertoire of other songs that males use to announce their territories to other males.

Then the team made a surprising find: In some areas they surveyed, there was more than one mating dialect. For example, two males singing different mating songs.

That finding led to Dr. Furnas’ hermit warbler research. He traveled throughout California and recorded and analyzed mating songs from more than 1,500 male hermit warblers during mating season, April through July, from 2009 to 2014.

What appeared to be causing the mixing of songs, he found, was wildfires.

“Hermit warblers are very sensitive to fire in the short term, and they typically abandon an area shortly after a fire. This creates a little bit of a vacuum, and other birds fill in that gap. The net result is that you get some areas with more than one dialect,” he said.

The new study also provides the first comprehensive description of hermit warbler mating song variants throughout California.

Results from the study have several uses:

  • Now that scientists have a library of the hermit warblers’ complex songs, they can use that data to better survey the hermit warblers and other species.
  • Although the hermit warbler is abundant in California, it does have some potential conservation concerns. In summer, the hermit warbler is only found in three states, and in Oregon and Washington the bird is hybridizing with a closely related but more aggressive species. One possible outcome is that California could ultimately be the only home to non-hybridized hermit warblers. The research could help with conservation efforts.
  • The findings could improve scientists’ understanding of how song diversity functions, helping them disentangle the complex relationships involved with biodiversity.

Read Dr. Furnas’ paper “link opens in new tab or windowWildfires and Mass Effects of Dispersal Disrupt the Local Uniformity of Type 1 Songs of Hermit Warblers in California.”

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CDFW Photos: Top Photo: Hermit_1: Hermit warblers are a migratory songbird that breeds in California, Oregon and Washington. Photo by Dr. Brett Furnas.

Media Contact:
Ken Paglia, CDFW Communications, (916) 825-7120

Categories: Science Spotlight
  • June 3, 2020

silver fish with green stripe on back with black dots in a net in a river with rocks
Adult Coho: Adult Coho Salmon released in Salmon Creek, Marin Co. (CDFW photo by Manfred Kittel).

redwood trees with creek and 6 scientist with nets and buckets looking for coho salmon fish with rocks and bushes and sun rays shining through the trees
Redwood Creek: CDFW biologists searching for juvenile Coho Salmon in Redwood Creek in summer 2014.

Coho salmon (Oncorhynchus kisutch), also known as silver salmon, have lived in California’s coastal watersheds for thousands of years. Today their populations have declined to just a fraction of historical levels, endangered by a wide range of factors. In Central California in particular, the situation is dire, with the species listed as endangered under both the state and federal Endangered Species Acts. Many populations are in danger of declining to the point of local extinction.

Recognizing the recovery of Coho salmon in central California’s streams and rivers as a high priority, the California Department of Fish and Wildlife (CDFW) is collaborating with NOAA’s National Marine Fisheries Service (NMFS), the U.S. Army Corps of Engineers (USACE), and other partner agencies and non-governmental organizations to develop and implement recovery actions. The tricky part is that there is no one-size-fits-all approach to saving the species.

Eric Larson, Fisheries Program Manager for CDFW’s Bay Delta Region, has monitored the decline of Coho on the Central Coast over the past three decades. As he sees it, an effective conservation strategy will do two things: prevent local extinction events, and implement specific recovery actions in streams that once functioned as Coho strongholds. “But,” says Larson, “each stream is a unique geographic and ecological system. In each watershed, any recovery actions -- including captive rearing and release efforts -- must be custom-tailored to that system to be successful.”

To date, some of those custom-tailored approaches include the following:

Captive breeding and monitoring (Sonoma County). Since 2001, CDFW has been working with NMFS, USACE and others to restore Coho populations in the Russian River basin in Sonoma County. A captive breeding program was developed at Warm Springs Hatchery, situated at Lake Sonoma Dam, to help re-establish populations in Russian River tributaries and other regional streams where Coho once flourished. The hatchery program relies on a genetically informed breeding matrix to minimize inbreeding and conserve genetic diversity. The program produces up to 200,000 Coho annually, which are released primarily as juveniles into tributaries of the Russian River and other streams, although some smolts and adults are also released in a few regional streams.

Concurrently, scientists from the University of California Sea Grant and Sonoma Water have been link opens in new tab or window actively monitoring juvenile Coho and adults returning to the Russian River system since the hatchery program began. The number of adult Coho returning to the river each year to spawn has gradually increased from just a handful in 2009, to more than 700 in 2017-2018.

Watershed restoration work and hatchery rearing of juveniles (Marin County). CDFW is collaborating with the National Park Service, USACE, State Parks and others to restore Coho salmon in Redwood Creek, which flows through the picturesque Muir Woods National Monument. The prolonged drought from 2013-2016, along with other factors, had brought Coho in Redwood Creek to the brink of local extinction, with fewer than 10 fish returning annually to the creek as adults to spawn.

From 2014 to 2016, approximately 200 juvenile Coho per year were collected in Redwood Creek and taken to Warm Springs Hatchery for rearing. The young salmon were grown to adulthood in the hatchery and, as three-year-old fish, released back into Redwood Creek in the winters of 2016 to 2018 to spawn. Tissue samples taken from juvenile Coho in summer 2017 and genotyped at the NOAA Southwest Fisheries Science Center in Santa Cruz confirmed that several of the fish released as adults in winter 2016 had spawned successfully and contributed to the persistence of this population in Redwood Creek.

Captive rearing (Mendocino County). Farther north, Coho populations are also declining in coastal watersheds such as the Garcia, Gualala and Navarro rivers. In recent years, the numbers of adult Coho returning to the Garcia and Navarro rivers have been below the threshold necessary to maintain viable populations, and no Coho have been detected in the Gualala River at all for several years. This low abundance raised concerns at CDFW and NMFS that without intervention, populations were likely headed towards local extinction.

For this reason, CDFW, NMFS and other partners developed a population recovery plan similar to those used for restoring Coho in the Russian River and Redwood Creek. As a first step, approximately 200 juvenile Coho were collected in October 2018 and again in 2019 in the Garcia and Navarro Rivers and taken to Warm Springs Hatchery. There the juveniles are being reared in captivity under the watchful eye of experienced hatchery staff. Meanwhile, CDFW and NMFS are developing plans for release of these fish, preferably as adults, back into their natal streams to spawn naturally. Although the fish could hypothetically be spawned at the hatchery and their offspring released back into the Garcia River, this option is unlikely due to hatchery space limitations. Releasing the Coho as adults also has the advantage of providing the released mature fish with free mate choice and exposing their offspring to natural selective pressures from the earliest life stage. Importantly, appropriate monitoring activities, including genetic parentage analysis, will be implemented to evaluate the success of the fish releases over the coming years.
The development and implementation of recovery programs, such as those outlined here, are urgently needed to conserve Central California coast coho salmon for future generations to enjoy and to make progress towards population recovery.

You can read more about efforts to conserve California’s Coho in the following documents:

CDFW Photos. Top Photo by Manfred Kittel. Warm Springs Hatchery, adjacent to Dry Creek. Picture taken from the top of Lake Sonoma Dam.

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Media Contact:
Harry Morse, CDFW Communications, (208) 220-1169

Categories: Science Spotlight
  • June 1, 2020

overhead view of 7 elk running in the snow with trees
Rocky Mountain elk in Modoc County taken during a CDFW survey in 2019.

Elk scat in weeds and dirt next to a sharpie pen for size reference
Scientists at UC Davis analyzed scat to determine where the elk originated.

A map of the elk’s journey from Tahoe to Sonora Pass
A map of the elk’s journey from Tahoe to Sonora Pass.

About a dozen years ago, California Department of Fish and Wildlife (CDFW) biologist Nathan Graveline heard rumors that a sole elk had been spotted in a highly unusual location – the Stanislaus National Forest, between the Clavey and Tuolumne rivers. At the time, scientists didn't have the technology to confirm the reports.

“Nobody knew where the elk came from. We weren't able to piece any of that together,” said Graveline.

Last September, scientists got word of another unexpected elk sighting, this time just south of Lake Tahoe in the Crystal Basin Recreation Area. “When I heard there was possibly an elk back in the area, I thought, ‘We’ve got to jump on this. If we can get a good DNA sample, we can figure out where the elk came from,’” said Graveline.

They set up trail cameras and were able to get a photograph of the elk. They also collected scat samples, which they sent to Dr. Benjamin Sacks, director of the Mammalian Ecology and Conservation Unit at the University of California, Davis’ Veterinary Genetics Lab. Through DNA analysis, Dr. Sacks and Ph.D. student Taylor Davis determined that the elk probably originated from a herd in the northeastern part of the state.

“We first estimated likelihoods of the observed genotype originating from each potential population based on the frequency of the alleles in those populations. We then obtained a probability or origin for each population by dividing its likelihood by the sum of all likelihoods for all populations,” said Dr. Sacks.

The report of an elk near Lake Tahoe was unusual in and of itself — but six weeks later the story got even more interesting. Scientists conducting a helicopter survey reported seeing a bull elk near Sonora Pass. 

Scientists went to the location of the reported sighting and were able to collect scat samples, which they sent to Dr. Sacks’ lab for analysis.

“We did the genotyping and it turns out it was the exact same elk that was tracked south of Lake Tahoe,” said Tom Batter, a Ph.D. candidate in Dr. Sacks’ lab. 

It appears scientists had on their hands a trailblazing elk — a Rocky Mountain elk that traveled 40 miles in six weeks and ended up farther south in the Sierra than had previously been reported.

“That boy was on quite a quest,” said Shelly Blair, a unit biologist in El Dorado County. “He likely traveled over some pretty rocky terrain, depending on which route he took. He probably had to cross over Interstate 80 or the 395 corridor at some point. Without the DNA, it would have been a total mystery as to where the elk came from.”

Kristin Denryter, coordinator of CDFW’s Elk and Pronghorn Antelope Program, said the bull’s journey is likely evidence of population growth among elk or herd densities that exceed the carrying capacity of the habitat.

“We know there’s great potential for expansion by bulls, and this means there could be recolonizations happening. We want our elk to be expanding and figuring out new habitats and going to new places. A bull elk like this might be figuring out new migratory routes and allowing for migration to persist. If he’s taking this route, then other elk and wildlife could be doing the same in the future,” said Denryter.

As to what motivated the bull elk to travel so far off the beaten path, Graveline says it may have been looking for a mate or new territory.

“He went farther south than he would need to for food, so I don’t think he was driven by that. This is a younger bull, and sometimes they get pushed out of a herd by a more mature bull,” he said.

Denryter added, “Younger males that are not competitive for mates are more likely to go off on their own or get pushed out of the herd. There’s absolutely a chance he could turn around and head back the way he came, but he’ll likely keep moving to find a mate.”

Although the elk is described by scientists as young, its exact age is unknown. Elk typically live 10-13 years in the wild. As far as threats in the wild – mountain lions hunt elk, but deer are their preferred prey. This elk’s biggest threat would likely be poaching, said Denryter.

Scientists are excited about the possibility that elk are expanding their range, but it’s also their job to prepare for corresponding conflicts.

“It’s kind of a double-edged sword,” said Denryter. “There’s risk of disease if elk come into contact with livestock while creating new migratory routes, and they can compete with livestock for forage. They can also cause vehicle accidents. Understanding the movements of elk and other wildlife is important so we can address these potential conflicts.”

CDFW would like help from the public in tracking the movements of elk populations statewide. Elk sightings can be reported online on the department’s website.

“If you see an elk — especially in places where you don’t normally see one — definitely take a photo with your smartphone and let us know,” said Denryter. “Smartphone photos are geotagged which will help us confirm the location. The online form allows you to upload photos and share any interesting observations. It’s really helpful to have this information so when there are conflicts or regulatory changes proposed we have data to help make informed decisions.”

CDFW Photos. Top Photo: A bull elk

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Media Contact:
Ken Paglia, CDFW Communications, (916) 322-8958

Categories: Science Spotlight