Science Spotlight

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  • March 19, 2020

Some of the 160 people who assisted Fish and Wildlife with it's March 1 desert bighorn sheep survey. CDFW photo.

man and woman using binoculars and a spotting scope to find sheep
Charles and Nicole Lozano of Chino Hills using binoculars and a spotting scope to locate sheep. CDFW photo.

mountains with shrubs in the fog
The San Gabriel Mountains, north of Ontario, where the sheep survey took place. CDFW photo.

The San Gabriel Mountains, north of Ontario, are a spectacular location for those who enjoy steep hikes and beautiful scenery. But one Sunday each year, those mountains are visited by people with a more specific agenda. They’re there to assist environmental scientists from the California Department of Fish and Wildlife in determining the number of desert bighorn sheep living there.

On March 1, 2020, about 160 volunteers gathered near the rugged terrain for the annual sheep count. Their goal was to use spotting scopes and binoculars to locate sheep, and determine and record their gender and approximate age. The volunteers attended a mandatory training session the night before in which CDFW staff briefed them on the purpose, counting techniques and best gear and supplies to bring for what can be a long day in tough elements. And as it turned out, March 1 was the one day in a stretch of about 20 that included a forecast of rain, and the forecasters nailed it. Between the fluctuating poor conditions – including a steady rain, low clouds, strong winds and even hail – nearly every volunteer struck out on being able to locate any sheep.

Fortunately, the annual count also includes an aerial survey the day before the boots-on-the-ground effort, and the weather was cooperative on Feb. 29. Eight CDFW employees took turns that Saturday flying in a Bell 407 helicopter over the locations where they’d likely find the sheep groups. Flights were limited to 2.5 hours before refueling was necessary. The crew of three on each flight was responsible for taking notes and guiding the pilot, using a handheld GPS to drop a waypoint at each observed sheep location, and capturing the animals with camera gear. The doors of the aircraft were removed to improve visibility for the spotters.

CDFW Senior Wildlife Biologist and survey coordinator Jeff Villepique said a key element of the effort is determining the health of the younger animals.

“One of the things we look at is how many lambs from last year have survived to this year,” said Villepique. “We did get some decent numbers that will help us determine the recruitment ratio and give an indication that the population is growing and doing well.”

When CDFW first started conducting these counts in 1979, the desert bighorn sheep in the San Gabriels numbered about 740. That dropped to fewer than 200 in the late ‘90s, and currently the population is back up to about 400.  Villepique said the numbers rise and fall based on food availability, habitat loss, weather patterns and the history of wildfires.

One group that enthusiastically supports the survey is the Society for the Conservation of Bighorn Sheep. Volunteer Debbie Miller Marschke has joined the effort multiple times, and despite the lousy weather conditions, was happy to be out in the mountains once again.

“When you get out in the environment and you’re with positive people, it’s not a wasted day, it’s a memorable day,” Miller Marschke said, smiling as she braved the downpour. “If I stayed home, I wouldn’t remember what I did a month later. I’m going to remember this day all year long.”

Categories: Wildlife Research
  • April 12, 2018

CDFW wants to know if, when and where you’ve seen an elk in California – and they’ve just created a new online reporting tool that makes it easy for members of the public to share this information.

CDFW scientists will use the raw data to help guide their efforts to study statewide elk distribution, migration patterns and herd movement, population size estimates, habitat use, health and diseases, and causes of mortality.

“We have limited resources and our scientists cannot scan the entire landscape,” explained CDFW Senior Environmental Scientist Pete Figura. “This tool provides a way for us to leverage the many sightings of the wildlife-watching public. People often get excited when they see elk, and hopefully now they will channel that excitement by reporting the location and time of their sighting to our department.”

There are three subspecies of elk in the state – tule, Rocky Mountain and Roosevelt -- and all three have expanded their range in recent years according to Figura.

CDFW has elk studies underway in the northern part of the state: one is focused on Roosevelt elk in Humboldt and Del Norte counties, and the other is focused on elk in Siskiyou and Modoc counties. Tracking and studying such a large mammal is a complex undertaking as elk herds are wide-ranging, and often graze and browse in areas that are not easily accessible, and there are only so many scientists to monitor their movements.

The launch of the reporting tool is just the latest effort to enhance the management of elk in California. Last year CDFW released a public draft of the Statewide Elk Conservation and Management Plan that addresses historical and current geographic range, habitat conditions and trends, and major factors affecting elk in California.

The plan will provide guidance and direction for setting priorities for elk management efforts statewide. CDFW is reviewing public comments on the plan and will incorporate appropriate changes into the final document prior to its release, which is expected soon.

CDFW Wildlife Branch Chief Kari Lewis has termed the plan an “important milestone” and explained that public feedback is a critical part of shaping the effort, which emphasizes a sharing of resources and collaboration with all parties interested in elk and elk management. This, she said, is essential to effectively managing California’s elk populations.

For more information about elk in California, please visit CDFW’s elk management webpage.

CDFW File Photo. Top photo: Group of Tule Elk.

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Categories: General
  • January 26, 2018

For residents of Humboldt and Del Norte counties, the majestic Roosevelt elk is a common sight. Although Roosevelt numbers were dwindling in California by the 1920s, conservative management strategies and limited hunting opportunities have helped them to rebound. Today, researchers have identified more than 20 distinct groups of elk in these two counties, many of which consist of well over 50 animals.

This conservation success story doesn’t come without a downside, though. Elk require large amounts of food to survive, and they tend to graze where food is most plentiful – often in agricultural areas and residential neighborhoods, where they cause damage to crops, landscaping, fencing and other private property.

Partly in response to rising concerns about property damage caused by the Humboldt and Del Norte herds, CDFW scientists are working on a wide-ranging, long-term study of Roosevelt elk population size and growth, herd movements, habitat use, disease and causes of mortality. The project, which is a collaborative effort with researchers from Humboldt State University, will collect critical baseline information about the animals that will help CDFW develop more robust and efficient methods for monitoring the herds, set future hunt quotas, inform local agencies about elk management and manage depredation issues. CDFW initiated this project in 2016 and expects to continue data collection efforts through 2018.

Tracking and studying one of the largest mammals in California is a much more complex undertaking than one might think. Roosevelt elk herds are wide-ranging and tend to graze in areas that are not easily accessible. Traditionally, CDFW relied on aerial surveys to monitor population trends of big game species such as elk, but such surveys are only feasible in a small portion of northwestern California because visibility is limited by steep terrain and dense vegetation. Ground surveys have similar constraints and are further limited by the small amount of occupied habitat that can be easily accessed from roads.

Given these constraints, CDFW scientists are employing multiple survey methodologies for the current study. Different techniques will be used in different habitat types. For example, in hard-to-reach areas, trail camera footage will be compared to visual surveys and used to collect herd composition data and estimate population size. Estimates will also be derived from analyzing the DNA contained in elk droppings.

CDFW also monitors the movement of the Roosevelt elk via electronic collars. There are currently 20 collared elk in coastal Del Norte and northern Humboldt counties and researchers hope to extend this project into central Humboldt County this winter, with plans to collar as many as 30 additional elk. Captured animals are also marked with ear tags, which allow for individual identification.

These survey efforts, and similar efforts elsewhere in the North Coast Roosevelt Elk Management Unit (EMU), are outlined in California’s Draft Elk Conservation and Management Plan, which is available for public review and comment through Monday, January 29. The plan provides guidance and direction to help set priorities for elk management efforts statewide.

CDFW photo: Environmental Scientist Carrington Hilson monitors a Roosevelt elk during a survey of the population.

Categories: General
  • January 19, 2018

An audio recording device in a semi-clear, plastic container on dark brown ground
The automated recorder model the scientists used. (CDFW photo by Brett Furnas)

Two avian researchers recently completed a groundbreaking study on the effects of climate change, based on the calls of California’s songbirds. By recording the sounds made by eight different songbird species, and tracking the dates they are most vocal and how frequently they sing, the scientists were able to develop a method to measure how the birds are adjusting to climate change.

CDFW Wildlife Ecologist Dr. Brett Furnas and William Jessup University’s Professor Michael McGrann analyzed data from two bird surveys, one done by CDFW and another led by William Jessup University, in the Klamath Mountains and Southern Cascades of northern California. Both studies used automated recorders to monitor bird sounds between 2009 and 2011. The results of their analysis, detailed in a research article entitled Using Occupancy Modeling to Monitor Dates of Peak Vocal Activity for Passerines in California, were published this month in a peer-reviewed, international journal of ornithology, The Condor: Ornithological Applications.

Furnas and McGrann’s study was prompted by the scientists’ concern that climate change could throw bird’s reproduction cycles out of sync with the seasons. Their work, which represents the first comprehensive assessment of songbird occupancy over approximately 15,000 square miles in California, earned high praise from Steve Beissinger, an expert on avian phenology at the University of California, Berkeley.

“Furnas and McGrann provide a textbook example of how to detect differences in the timing of nesting among bird species using information on the peak date of singing derived from surveys and automated recorders,” Beissinger said. “Their results support recent findings of a five-to-twelve day shift forward in the timing of peak singing by California birds in the nearby Sierra Nevada and coastal ranges in response to climate change.”

Because birds’ songs are correlated with their breeding behavior and are easily identifiable to species, the scientists found them to be a useful tool to provide new baseline data for the birds of northern California. Working together, they identified the precise dates of peak vocal activity for eight songbird species: Hutton’s vireo, hermit thrush, dark-eyed junco, Nashville warbler, MacGillivray’s warbler, yellow warbler, western tanager and black-headed grosbeak. In addition to gathering baseline data, Furnas and McGrann developed a method to track advances in the timing of vocal activity in the coming decades.

Male songbirds sing for several reasons -- including to advertise their territory or to find a mate with which to breed. When birds are at their most vocal, they are usually near the height of their breeding season, Furnas explained.

Much like the call of the imperiled “canary in the coal mine,” changes in the frequency or timing of these native birdsongs can serve as barometers of the cumulative impact of climate change.

“When the canary starts singing you know that there is a danger, such as a buildup of dangerous gasses in a mine,” Furnas explained. “When the birds in our study start singing earlier in the season, they are warning us that climate change is starting to disrupt complex ecological cycles that developed slowly over millions of years of evolution.”

One of the most interesting findings of the study so far is a hint in the baseline data that migratory birds may be at greater risk than non-migratory birds. “We found the highest singing activity for migrant birds spanned a shorter number of days than the highest singing activity for non-migratory birds,” Furnas said. “This could be because migratory birds have less flexibility to shift the timing of their breeding cycle. If they are prompted by increasing temperatures to migrate earlier in the year, they may arrive at their breeding grounds to find they don’t have enough insects to eat.

“Migratory birds have to compress a lot of activities into a shorter time period with less margin for error,” Furnas explained. “Think of it like scheduling a short holiday somewhere nice, but when you show up, bad weather cancels out a lot of your itinerary.”

This, in turn, negatively affects the very biodiversity that CDFW is responsible for monitoring.

“If all the species adjusted their ecologies similarly, perhaps that would be OK, but unfortunately, we expect that different insects and birds will react in different ways leading to a mismatch of conditions,” Furnas said.

Both CDFW and William Jessup University plan to continue bird surveys over the long term so that California has the information to support effective management of climate change and other conservation challenges.

Top photo: Singing hermit warbler, one of the species addressed in the study. (CDFW photo by Michael McGrann)

Categories: Wildlife Research
  • November 8, 2017

a white-spotted fawn lies in straw as its leg is measured
CDFW Environmental Scientist Brian Ehler measures the hind-foot length on a fawn captured near Medicine Lake for a mule deer study.

four deer are suspended in the air, in safety harnesses, from a red helicopter
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.

Categories: Wildlife Research
  • August 15, 2017

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 link opens in new windowentire Winter Issue 103 (PDF) in high resolution, or browse individual articles in low resolution.

Categories: California Fish and Game Journal, Wildlife Research
  • July 25, 2017

Five deer wade knee-deep in blue lake water
cute face of a mule deer

Three people check and attach a collar to a doe
doe on a hillside wears a research collar
Mule deer buck in a dry meadow
Two people collect deer pellets from a trail
Doe and fawn look out from a dry-grassy ridge

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.”

Categories: General
  • June 13, 2017

A buck with a collar walks through brush on a hillside
A young woman attaches a trail camera to a dead tree trunk.

Deer population estimates are an important element of the California Department of Fish and Wildlife’s (CDFW) management decisions regarding the species – including setting quotas for deer-hunting seasons, acquiring land and identifying habitat improvement projects. Historically, CDFW has relied upon helicopter surveys to obtain these population estimates, but such surveys can be problematic. While they are effective in open and largely flat areas, they are less so in tree-laden areas where deer are hidden from sight. They can also be extremely expensive.

Now, thanks to emerging DNA technology, scientists are exploring a less invasive, cost-effective alternative: Analysis of what the deer leave behind.

The use of DNA is not new, of course – CDFW has used hair or tissue samples to extract DNA and identify individual animals for years. But scientists are finding that the painstaking collection and analysis of deer droppings is particularly useful because it allows them to gather the necessary information without physically touching (or stressing) the animals. And that, one might say, is the “bottom line.”

Fecal DNA analysis is being used by wildlife biologists in the North Central Region as part of a six-year region-wide study of mule deer (Odocoileus hemionus) that will provide population estimates in areas where data has previously been lacking. CDFW scientists, in cooperation with UC Davis, will use the deer pellets to take a genetic “fingerprint” designed to help estimate deer populations.

Starting in 2016, a crew began setting transects for pellet collection in the standardized sampling locations (known to hunters as deer zones X6a/b, X7a/b and X8) which are located in Lassen, Plumas, Sierra, Nevada, Placer and Alpine counties. After starting points were randomly selected, habitat information and pictures were collected along with fresh pellets. After the pellets were removed from the area in an initial sweep, scientists revisited the transect once a week for three more weeks to collect new samples. Between July and September of 2016, biologists visited 43 different transects in the summer range and collected and analyzed 458 fresh pellet samples. Staff also captured 20 does and seven bucks and fit them with satellite collars that produced data that helped identify summer home ranges.

CDFW will also use DNA to identify individual deer to help gather buck/doe/fawn ratios. Biologists will then combine the DNA data with home range data from collared deer to calculate the estimated number of deer in the population. This year staff have already completed another 36 plots and collared 18 more deer. Another series of pellet collections is scheduled next year, with a goal of continuing until all 17 counties in the region have been sampled.

Although several DNA projects are occurring across the state, this project is the largest landscape-level study for deer in California. The study is funded through CDFW’s Big Game Account, a dedicated account that provides research and management funds for game species. The University of California will conduct the laboratory work and statistical analysis.

Categories: Wildlife Research
  • May 17, 2017

A fisher climbs a tree trunk at night

Scientists with the California Department of Fish and Wildlife (CDFW) and Oregon State University recently published the results of a population study on fishers (Pekania pennanti) in northern California and southern Oregon. Led by CDFW Wildlife Statistician Dr. Brett Furnas and three coauthors, CDFW Senior Environmental Scientist Richard Callas, CDFW Research Analyst Russ Landers and Dr. Sean Matthews of Oregon State University, the study produced the first-ever robust estimates of density and size of the fisher population in northern California.

“This is the first time we’ve come up with a solid number of fishers, which is a starting point for tracking and monitoring populations,” Furnas said. “One of the most important tools we have used so far to help this species is reintroductions, so now -- with a baseline established and ongoing surveys planned -- we’ll be able to see if the population is really rebounding over time.”

Fishers in northern California and southern Oregon represent the largest remaining population in the Pacific states. The species once ranged from the state of Washington southward through Oregon and California. Currently, fishers occupy only a small portion of their historical range in that region. In California, fishers are found in the northern areas of the state and a small, isolated population occurs in the southern Sierra Nevada Mountains.

CDFW and the U.S. Fish and Wildlife Service have been petitioned on several occasions to list fishers as threatened or endangered under their respective Endangered Species Acts.

In 2016, while considering fishers in the southern Sierra Nevada Mountains of California, the California Fish and Game Commission voted that the petitioned action was warranted in part, choosing to accept the petition in the context of the Southern Sierra Nevada Evolutionarily Significant Unit, and adopted findings to that effect, which were published on May 6, 2016. Although fishers are relatively well-distributed in northern California and in portions of southern Oregon, data from existing surveys and prior studies was used to estimate abundance. This information is critically important to assess the status of fishers and serve as a baseline for conservation efforts.

Furnas and his coauthors used data from camera traps, hierarchical modeling of detections and non-detections of fishers from the cameras, and information about fisher home range size to develop their estimate of population size. They estimated that approximately 3,200 fishers occur within the northern California and southern Oregon study area, with an average density of 5.1 to 8.6 fishers per 100 square kilometers.

Estimating the sizes of wildlife populations is challenging, particularly for species such as the fisher that are difficult to observe and occur over large areas. A final population estimate for the fisher would not have been possible without the cooperation of a variety of federal and tribal agencies, universities and private landowners who shared datasets that were combined to complete the modeling. With these data, Furnas and his coauthors demonstrated that estimating the population size of the fisher at large geographic scales is feasible. They also suggested that the methods used in their research could be used to estimate the abundance of other carnivores, including black bear, gray fox and coyote.

The study was published in the journal Ecosphere. link opens in new windowMore information / view publication

Categories: Wildlife Research
  • March 29, 2017

Pronghorn antelope (Antilocapra americana) were once one of the most numerous large mammals in California, with populations estimated to have been as high as 500,000 prior to the Gold Rush era. In the mid-1800s, pronghorn were nearly extirpated by market-shooting to feed California’s rapidly expanding human population.

The remaining population of pronghorn has long been understudied. Prior data collected on the species have been limited to herd counts and habitat selection. In recent years, there has been growing concern over pronghorn populations, particularly in northeastern California. During the harsh winter of 1992, the number of pronghorn dropped almost 50 percent to an estimated 5,000 individuals. The northeastern portion of the state currently supports a population of approximately 4,500 animals that occur primarily in Modoc, Lassen, Siskiyou and Shasta counties and has been fairly stable, with slow declines, since about 2000. The herd’s inability to rebound has prompted scientists to try to understand the specific conditions leading to the declines.

In 2016 the Institute for Wildlife Studies (IWS) completed a two-year study, with funding from CDFW’s Big Game Management Account, which explored aspects of the pronghorn population on the Modoc Plateau. The study involved 48 does (adult females) and 42 fawns that were radio-collared and followed until their deaths or the study’s end. The researcher’s objectives were to learn more about the pronghorn use of habitat, aspects of their reproduction and factors affecting survival of does and fawns.

The researchers found that for most of the year, pronghorn used open areas with less shrubby and more herbaceous vegetation within their sagebrush-steppe habitats. But during fawning, when does need to hide their young, they shifted to spending more time in areas with greater densities of shrubs and juniper trees. The annual survival rate for does in the study was 69 percent, which is low compared to other pronghorn populations. Mountain lions accounted for 80 percent of predator-related mortalities, most of which occurred during and just after the peak birthing period when does are most vulnerable. Fawn survival averaged 44 percent, a higher-than-typical figure, with unknown causes (37.5 percent) or suspected coyote predation (21 percent) accounting for most fawn mortalities.

The adults’ increased use of shrubby areas and conifer woodlands during fawning suggests an important factor in the population’s continued decline. Juniper woodlands have been encroaching on the sagebrush-steppe habitat in the Modoc Plateau for decades, and these juniper trees provide areas of concealment for ambush predators such as mountain lions. Most ungulate studies demonstrate that adult survival plays a more critical role in population stability than juvenile survival. CDFW may be able to reduce adult pronghorn mortality through habitat restoration – the removal of encroaching junipers could help to reduce predations by lions, and potentially increase the Modoc pronghorn population.

link opens in new windowRead complete report.

Categories: General
  • February 14, 2017

Arborimus albipes, a CA Critically Imperiled Species of Special Concern

The white-footed vole is one of the least-studied (and most difficult to catch!) mammals in North America. CDFW Environmental Scientist Dr. Scott Osborn, his collaborator Dr. Tim Bean of Humboldt State University’s Wildlife Department, and a small team of field biologists know that better than anyone – they spent the summer of 2014 setting traps for them in Humboldt and Del Norte counties. Designated a Species of Special Concern by CDFW, only nine records of the species were known in California prior to their study, which was aimed at determining how environmental conditions, such as climate (and future climate change), might affect their distribution.

Habitat modeling by Bean (based on the previous records) identified areas with high habitat suitability for the white-footed vole. Ten study sites were chosen along the North Coast for the field study, including three where voles had been successfully trapped in the 1990s. Using live traps (both pitfall traps made of two coffee cans taped together and Sherman live traps baited with oats and peanut butter), the team successfully trapped three voles. Notably, one of these was the first recorded capture of a white-footed vole in Del Norte County. All three voles were returned unharmed to their capture site after basic measurements and assessments of food plant preferences were made.

Although three voles might not seem like a large return on the investment of many hours of field work, the team actually had one of the highest capture rates of white-footed voles of any small mammal study in its geographic range, which includes coastal Oregon and the North Coast of California. Vegetation plots suggest that white-footed voles are tightly associated with stands of red alder trees – so now the biologists know that’s a likely place to find them. The habitat modeling work indicates that suitable habitat may currently exist as far south as Mendocino County, which is outside the known geographic range of the vole. On the other hand, it is possible that this species’ range may contract northward in a warmer and drier future. link opens in new windowOpen the Full Report (PDF)

bucket sunk into ground under shrubs   A tiny brown vole sits on green leaves in a metal bucket

Categories: Wildlife Research
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