Science Spotlight

Rocky Mountain elk in Modoc County taken during a CDFW survey in 2019.


Scientists at UC Davis analyzed scat to determine where the elk originated.


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

Veterinary staff assess deceased deer


Veterinary staff take samples of deceased cervid


Veterinary staff take samples of deceased cervid

CDFW scientists, wildlife officers and other staff are pulling out all the stops to fight a wildlife disease of major concern from crossing state lines and infecting native deer and elk populations.

Chronic Wasting Disease (CWD) is a contagious, always-fatal neurological disease that affects cervids (deer, elk and moose). In North America, the disease is currently found in captive and wild cervid populations in 24 U.S. states and two Canadian provinces. It has been detected in captive elk and sika deer in South Korea and free-ranging reindeer, moose, and red deer in Norway and Finland.

To date, a combination of legislation and geography have kept this disease at arm’s length from California, but the threat is still very real.

“All of us – scientists and wildlife managers, landowners and hunters – need to join forces and work together to keep this disease out of California, or the future could be disastrous for our native herds,” said CDFW Wildlife Veterinarian Brandon Munk, who participates in a multi-agency task force to fight CWD.

For California, this means two things: continuing to enforce strict cervid (animals and parts) importation and movement regulations, and ramping up disease surveillance efforts. This deer season, CDFW will be setting up voluntary check stations for deer hunters throughout California. Here trained staff will collect lymph nodes from the neck of harvested deer – a process that takes only minutes and is minimally invasive to the surrounding tissue. While waiting, hunters can get their tags validated and learn more about how to help prevent the introduction of CWD to California.

Once established, CWD is notoriously difficult to fight. The disease is spread by direct contact with infected animals or environments contaminated by the infectious agent called “prions.” Environmental contamination seems to play a very important role in the spread and maintenance of this disease. Once the environment is seeded with these prions, eradication is difficult – if not impossible – as prions are extremely difficult to remove from the environment or to disinfect. Prions can also remain infectious in the environment for years. Even controlled burning and freezing temperatures do not remove the threat. Most attempts to eradicate this disease have failed, and scientists in other states have had limited success in their efforts to control its spread.

CWD is also difficult to detect, in part because the outward signs often do not manifest until several years after initial infection. Currently, there is no effective live-animal test and there is no vaccine. Systematic testing of hunter-harvested deer is one of the most widely used surveillance methods available. Additionally, it is one important method to help ensure the disease has not entered the state and will help ensure CDFW can detect CWD early should it ever reach California. Early detection of CWD is the first and most important step to effective management of this disease.

CDFW has established a Chronic Wasting Disease Task Force to lead efforts preventing the spread of CWD to this state. Members include CDFW staff (biologists, veterinarians, communications officers and wardens), Fish and Game Commission employees and California Animal Health and Food Safety veterinarians. The task force is reaching out to the public and other local, state, and federal agencies to help with surveillance efforts, educating sportsmen about how they can do their part to prevent the spread of CWD and preparing a comprehensive management plan to allow for rapid response if the disease ever does make it to California.

“We are very lucky that to date, no California deer or elk has tested positive for CWD – but we’re not taking it for granted,” Munk said. “We urge hunters to educate themselves about this very real threat, and to do their part to make sure that we keep it out of California.”

CDFW has produced a short video on preventing the spread of CDFW, including a demonstration on antler removal and proper butchering techniques. You can also find background information, additional links and updates on California’s efforts to fight CWD at www.wildlife.ca.gov/CWD.

To find a CDFW check station to get your deer or elk checked, please visit www.wildlife.ca.gov/CWD or call (916) 358-2790.

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CDFW Photos. Top Photo: Veterinary staff takes and examines samples from deceased deer.

CDFW Environmental Scientist Brian Ehler measures the hind-foot length on a fawn captured near Medicine Lake for a mule deer study.


CDFW Environmental Scientist Brian Ehler measures the hind-foot length on a fawn captured near Medicine Lake for a mule deer study.

Driving up Interstate 5 through Siskiyou County in northern California, one cannot help but take notice of the looming, majestic land mass of Mount Shasta, the largest volcano in the Cascade system.

In this rugged region of the Golden State, mule deer are an iconic species, valued by recreationists and required by wild carnivores who prey upon them for nourishment. Mule deer are considered a “foundation species” because the large landscapes that are necessary for their survival can also be home to a vast array of other wildlife and plant species. But mule deer populations have dramatically declined in recent decades across many western ranges, and in Siskiyou County, this decrease has prompted researchers from CDFW and the University of California, Santa Cruz to partner on a multi-year effort to investigate the population dynamics of this high-profile species.

Since 2015, 51 adult female mule deer and 37 fawns have been captured in the Mount Shasta region. Biological samples, including blood and parasites, have been collected, physical measurements of body condition and age recorded and telemetry collars attached to each subject. Collars on adult deer provide a GPS location every hour and alert researchers when a mortality occurs. The collars also document movement details, including migration routes and the location of critical winter and reproductive ranges. The fawn collars feature location beacons that allow researchers to monitor both general movements and when a mortality has occurred. Once a mortality alert is sent from a collar, a search of the site and an examination of the carcass ensues to determine if the deer died from predation or other causes, such as disease or malnutrition. The collars have timed releases and are set to drop off the animal after 18 months. Researchers can then reuse the collars after retrieving them by following a GPS signal. This high-tech, high-resolution documentation of deer behavior is vital for prioritizing the conservation value of landscapes so they may be better protected in the future.

With the recent arrival of gray wolves to northeastern California, predators are a key focus of the mule deer project. Understanding the influence this large canid will have on natural prey species begins with establishing baselines of how current predators -- including mountain lions, bears, bobcats and coyotes -- are affecting prey in this region. Mountain lions, which rely on deer as the primary component of their diet, are a major focus of this study. Researchers have captured and affixed five adult mountain lions with GPS telemetry collars, allowing them to track and study rates of predation, feeding patterns and diet composition.

The analysis of fecal DNA combined with new statistical techniques is another way to study population density and composition across broad landscapes. DNA analysis allows researchers to determine the sex and identity of an individual deer, which is used to estimate densities and gender ratios. Researchers are collecting fecal samples throughout the mule deer’s summer range, in the hopes of reliably extrapolating estimates of density and sex ratios across the entire region.

This project, which began in 2015, is scheduled to continue into 2019, as researchers strive to gain further insight into the lives of mule deer and predators across this ecologically complex and breathtakingly beautiful region of the state.

California Department of Fish and Wildlife photos.
Top photo: Mount Shasta in winter.

The latest issue of California Fish and Game, CDFW’s scientific journal, is now available online. This century-old quarterly journal contains peer-reviewed scientific literature that explores and advances the conservation and understanding of California’s flora and fauna.

The endangered salt marsh harvest mouse (Reithrodontomys raviventris) graces the cover of California Fish and Game, Volume 103, Issue I. Researchers ventured into the pickleweed to study the tiny mouse, which is endemic to the marshes surrounding the San Francisco Estuary Bay and its tributaries. The mice were fitted with tiny radiotelemetry collars and tracked for three years. Researchers documented some curious behavior in the resulting paper, “Potential evidence of communal nesting, mate guarding, or biparental care.” The accompanying photos provide a fascinating glimpse into an active nest.

Another paper, “Documentation of mountain lion occurrence and reproduction in the Sacramento Valley of California,” explores the potential for mountain lions to exist in fragmented habitats if there is adequate connectivity with larger blocks of suitable habitat and sufficient prey. The study used camera traps to document populations of mountain lions in the Sacramento Valley’s Butte Sink, which is made up of relic riparian habitats interspersed with managed wetlands. The photos show healthy mountain lions moving through habitat that has long been considered unsuitable due to extensive agricultural and urban development.

The article, “Mussels of the Upper Klamath River, Oregon and California,” reports on sampling efforts that expand existing baseline population data on freshwater mussels in the Upper Klamath River. The sampling efforts may ultimately assist with protection, mitigation and enhancement efforts for large bi-valve species.

The final paper provides insights into the benefits deer and elk derive from licking mineral rocks. Researchers took samples of “lick sites” that were used by California black-tail deer (Odocoileus hemionus columbianus) and Roosevelt elk (Cervus canadensis roosevelti) in the Klamath Mountains, Siskiyou County. After performing a detailed analysis of the elemental content of each lick site, the researchers concluded that each lick site offers a different smorgasbord of minerals, and in varying concentrations. The study’s objective is to begin identifying, classifying, and analyzing important mineral lick sites to benefit future ungulate management efforts.

As it has for the past 103 years, California Fish and Game continues to publish high-quality, peer-reviewed science that contributes to the understanding and conservation of California’s wildlife. We look forward to witnessing the contributions of the next installment.

Download the entire Winter Issue 103 (PDF) in high resolution, or browse individual articles in low resolution.

As California deer hunters head to the fields, forests and mountains this summer and fall, their experiences will provide wildlife biologists with key data on the health of the state’s deer herds. Wildlife biologists are already seeing the benefits of a 2015 regulation change requiring all deer tag holders to report how they did – successful or not – along with how many days they actually spent hunting, even if they never made it out at all. A record 84 percent of deer tag holders submitted harvest reports for 2016.

“We’re getting more accurate and precise numbers for harvest than we’ve ever had before, which is critical for calculating the tag quota for the next year and conserving our deer populations for the future,” said Stuart Itoga, a senior environmental scientist with CDFW and the state’s deer program coordinator.

Until recently, accurate deer harvest data had proved elusive. Prior to 2015, only successful California deer hunters had to report their take and only about 30 percent of those actually complied. CDFW supplemented the harvest data with numbers collected from game processing facilities, an inefficient process that still left an incomplete picture.

“It’s Wildlife Management 101,” Itoga said. “You have to know what your population is, what’s coming in and what’s going out. We needed to have better numbers.”

Following the mandatory reporting requirement in 2015, submittal rates for deer tag harvest reports jumped to 50 percent. In 2016, a $21.60 non-reporting penalty took effect, which applies to the purchase of future tags, and boosted reporting to the all-time high.

Mandatory deer tag reporting data is just one of a number of new tools that has CDFW deer biologists excited about their ability to better assess California’s deer herds. An innovative DNA study of deer feces promises to give biologists new information about the size and characteristics of the state’s deer population.

CDFW has also greatly expanded the use of deer tracking collars, thanks to improved technology. Since 2016, CDFW has affixed the relatively lightweight, remotely programmable, GPS tracking devices on 350 deer to learn more about their preferred habitat, in-state and out-of-state migration routes and sources of mortality other than hunting. Advanced camera technology also promises to improve the data collected from CDFW’s aerial and ground-based population surveys. A new computer model is being developed to incorporate all of these new data sources into more sophisticated, accurate and precise deer population estimates.

“It’s really an exciting time to be doing this type of work,” Itoga said. “We’ve always used the best available science, but with technology moving at the pace it’s moving now, we have tools available to us now that we didn’t have even five years ago.”

Management changes can happen more quickly as a result. For the upcoming 2017 deer hunting seasons, for example, deer tag quotas were cut in half in three highly desirable, Eastern Sierra X Zones – X9a, X9b and X12 – as a result of new data and field work that showed that migratory deer in these areas suffered from the long, intense winter.

“Winter survival was poor,” Itoga said. “Our hope is that if we reduce the harvest this year, the populations will have a chance to rebound and increase next year.”