Science Spotlight

These pregnant females will bolster the population of a newly established herd as well as provide an infusion of fresh genetic material to helps ensure their new herd’s health and long-term survival.


Outfitted with an ear tag and two tracking collars, this ram awaits delivery to a new herd where it’s hoped he will infuse the population with fresh genetics


Among the goals of the Sierra Nevada Bighorn Sheep Recovery Plan is the establishment of 12 viable herds across their historic range. CDFW’s capture and relocation efforts over the years have helped establish 14 herds today across 150 miles of their historic range.


These Eastern Sierra bighorn sheep are being prepared for their flight to a new home and new herds.

Seven animals.

Can just seven Sierra Nevada bighorn sheep really make much of an impact on the species’ future?

CDFW scientists believe so, which is why they came away pleased with the results of their annual spring helicopter capture this past March. Limited to three days of work due to strong winds and bad weather, the effort resulted in the capturing, collaring and relocation of seven sheep to new herds high in the Eastern Sierra.

Although the final chapters have yet to be written, the saga surrounding the Sierra Nevada bighorn sheep, one of the rarest large mammals in North America, is shaping up to be a 21st century wildlife success story.

A unique subspecies found only in the Sierra Nevada, historic populations numbered in the thousands. Their steep population decline began in the 1800s as a result of competition from livestock grazing, unregulated hunting and the transmission of disease from domestic sheep. Drought and predation further hammered their numbers, which dwindled to about 100 animals in just three herds by the mid-1990s. State and federal officials declared them endangered in 1999.

Today, less than 20 years removed from those dramatic listings, there are 14 different Sierra Nevada bighorn sheep herds spread across 150 miles of the iconic mountain range. About 600 bighorn sheep are now eking out a living atop the Sierra’s highest peaks. Sierra Nevada bighorn sheep are present once again inside Yosemite National Park and Sequoia National Park after a 100-year absence.

CDFW’s role is itself unique as a state agency tasked with leading the recovery of a federally listed endangered species. Sierra Nevada bighorn sheep are recolonizing their historic range – with a major assist from CDFW’s twice-yearly captures, collaring and strategic “translocations.”

This spring, three males and four pregnant females were captured from two established herds and translocated to two newly reintroduced herds – one along their western range inside Sequoia National Park and another herd in Inyo County at the southernmost extent of their range.

“Whenever we start these new herds, we like to move a minimum of 20 females as well as additional rams over time,” explained Tom Stephenson, a CDFW senior environmental scientist based in Bishop and the leader of the Sierra Nevada Bighorn Sheep Recovery Program. “At that point, we feel the population has enough animals to begin growing at a high enough rate and also has sufficient genetic diversity.”

Before the animals are relocated, a CDFW team records their vital statistics. Ultrasound machines are used to measure body condition and determine pregnancy status. The animals are outfitted with identifying jewelry – color-coded ear tags, VHF and GPS collars that allow biologists to identify them and track their movements for years in some cases.

All the high-tech, intensive monitoring has paid dividends with new appreciation and understanding. Once believed to always migrate to lower elevations in the winter, CDFW scientists have learned that many sheep ride out the Sierra Nevada’s inhospitable winters at 11,000- to 14,000-foot elevations.

“They are really tough,” Stephenson said. “But they’re able to do that because they put on large amounts of body fat in the summer when they’re on quality habitat. They are essentially hibernating standing up in the alpine. They’ve got an environment up there that is wind-scoured so they can find some food. They’re not having to move around much, and they’re relatively free from predators when they’re up in those altitudes in the winter time.”

Not every sheep captured is relocated.

Helicopter crews this spring attempted unsuccessfully to capture rams in the northernmost part of their range, collar them and return them to their same herds. CDFW biologists are keeping close tabs on the Mount Warren Herd near Lee Vining in Mono County in particular and its proximity to domestic sheep grazing on public land. Sierra Nevada bighorn sheep are disease-free and CDFW biologists want to keep them that way.

While populations have met or exceeded some recovery goals, eliminating disease – or the risk of disease – remains a significant benchmark and key to delisting or down-listing the species from endangered status.<

“There are a lot of bighorn sheep populations throughout the West that continue to struggle with disease,” Stephenson said. “So we’ve worked really hard with public land managers as well as private individuals in the Eastern Sierra to try and ensure our bighorn sheep don’t come into contact with domestic sheep.”

CDFW photos courtesy of Andrew Di Salvo. Top Photo: A helicopter crew delivers four bighorn sheep to CDFW's base camp where vital statistics were recorded, blood was taken, and the sheep were outfitted with identifying ear tags and tracking collars.

A dwindling population of a tiny owl in Southern California has a chance at a comeback, thanks to a collaborative effort by scientists from CDFW, the San Diego Zoo’s Institute for Conservation Research (ICR), Caltrans and the U.S. Fish and Wildlife Service.

The Western burrowing owl (Athene cunicularia hypugaea) is currently listed as a Species of Special Concern, and nongame scientists have long been concerned about their viability and survival. Breeding populations have especially declined in the central and southern coastal areas, due in large part to a combination of habitat loss and eradication of the ground squirrels that dig out the burrows where the owls make their nests. In San Diego County specifically, the once-widespread population has been reduced to a single breeding node in the Otay Mesa region, just north of the Mexico border.

Two groups in particular have been monitoring these owls carefully, in an effort to help. Biologists from Zoo’s ICR have spent seven years assessing owl population status and productivity, including assessing the feasibility and effectiveness of artificial burrows, refining techniques to help the ground squirrels thrive and disperse into new areas and developing a system of identifying potential new locations where the owls might thrive. Much of ICR’s owl research has been conducted at Brown Field, a small municipal airport near the border within the City of San Diego, and on an adjacent property owned by Caltrans.

Meanwhile, about 10 miles from the Brown Field study site, CDFW scientists have spent a decade working to create more suitable burrowing owl habitat at Rancho Jamul Ecological Reserve (RJER). Efforts there included installation of artificial burrows and mowing the tall grass to foster a low-growing grassland suitable for burrowing owls and ground squirrels. Despite their best efforts, CDFW scientists studying the Rancho Jamul site have experienced many years of disappointment -- although wintering owls have shown up every year, none have stayed and attempted to breed on the property. But conditions have been improving over the last four years, thanks to the implementation of a grazing program that reduced dense thatches of old grasses and expanded areas of open ground. As habitat changed at Rancho Jamul, CDFW scientists observed more squirrel burrows, and the conditions seemed just about right for the owls.

This spring, an approved development project at Brown Field began to take shape – and it became evident that the timing for an owl translocation project was ripe at last. Thanks to efforts by Caltrans, which incorporated burrowing owl habitat restoration as part of their mitigation effort for a nearby highway, CDFW staff believed the owl population to be strong enough to support a translocation effort. Also the spring season, just prior to egg-laying, is likely the optimum time to move the animals. After looking at many options, scientists decided to try to move five pairs of breeding owls to RJER in the hopes that they would establish a new population and thrive.

The full conservation team – which included CDFW, the U.S. Fish and Wildlife Service, the City of San Diego, Metro Air Park, Schaefer Ecological Solutions and the San Diego Zoo – was on board and ready to move the owls. In March 2018, the team caught five pairs and moved them to hacking cages at RJER. The owls lived in the cages for about one month to give them time to acclimate to their new surroundings. By the time the cages were removed, each female had laid at least one egg in the artificial burrow chamber.

CDFW Environmental Scientist Dave Mayer has worked on this project for years and is anxious to see efforts at RJER finally pay off. The presence of the eggs, he said, was thrilling to see. “More owls, and at diverse locations, is what it will take to conserve this species in San Diego County. This first step was a long time coming, but I have all my fingers crossed that it’s going to work.”

This successful multi-agency partnership will continue long past the actual translocation day. Scientists banded the owls and fitted some with radio transmitters. ICR staff will monitor the owls themselves, while CDFW staff will monitor the grassland and the grazing program, and perform inspections and repairs of the artificial burrows twice a year. After five years, CDFW will perform regular monitoring of the owls, the habitat and associated grazing practices, and the general status of the ground squirrel population.

Mayer is proud of the work achieved so far in this unusual project. “We built a better mousetrap, with the Zoo’s help,” he says. 

General information about California’s bird species of special concern can be found on the CDFW website, along with the species account (PDF) for the burrowing owl and information about Rancho Jamul Ecological Reserve.

The San Diego Zoo has also issued a news release with more details about the burrowing owl translocation project.

All photos © San Diego Zoo Global, all rights reserved

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Wildlife Officer Pat Freeling replanting dudleya.


Wildlife Officer Will Castillo replanting dudleya.

Last week, a team of California Department of Fish and Wildlife (CDFW) staff and volunteers spent hours working to replant than 2,000 Dudleya succulents that were seized after a poaching investigation. The plants were meticulously returned to the Mendocino and Humboldt county cliffs from where they were stolen weeks before.

The sheer volume of plants made it necessary to put a call out for help from volunteer botanists. The response was overwhelming. More than 20 succulent experts from the California Native Plant Society and U.C. Santa Cruz arboretum, along with National Parks Service personnel, assisted CDFW wildlife officers and seven environmental scientists on the replanting project. The replanted succulents will be monitored over the next week to ensure the greatest chance for survival.

CDFW Environmental Scientist Michael van Hattem calls Dudleya “the botanical version of abalone,” in the sense that they are a sensitive species, dependent on a very specific habitat. Without a concerted effort to reverse the effects of such a large poaching operation, he says, the ecosystem would be irreversibly damaged.

In March 2018, CDFW law enforcement officers uncovered an international conspiracy to strip the succulents from sea cliffs and ship them overseas to other countries, including Korea and China, where they are prized for decorative purposes. So far, there have been three significant poaching investigations. In the first case, prosecuted in Mendocino County, the subject was found guilty and fined $5,000. A second case is also currently pending in Mendocino County. 

The third recent case was out of Humboldt County, where wildlife officers seized well over 2,000 succulent plants from three suspects. Prosecution of that case is also pending. This week, the Humboldt County District Attorney’s Office released all but 10 of the plants from evidence to allow the team to replant them at the location where taken. 

“Our wildlife officers and partners have gone to extraordinary length to investigate and stop a new poaching threat in California,” said David Bess, Deputy Director and Chief of the Law Enforcement Division. “We can't think of a better project to work on through Earth Day weekend.”

CDFW Photos. Top Photo: Wildlife Officer Will Castillo replanting a Dudleya succulent.

California’s drought emergency was officially declared to be over last year, but its deleterious impact on fish habitat is still being felt in many parts of the state -- especially in arid parts of Southern California. In order to help offset these effects at one site in northern San Diego County, CDFW biologists and other staff recently toiled to create spawning beds for rainbow trout.

The Sweetwater River is a second-order stream located within Cuyamaca Rancho State Park. The underlying rock is granite, which, as it erodes, creates sand that accumulates in the low-gradient portion of the river. Previous surveys in the Sweetwater River revealed a lack of high-quality spawning habitat for the rainbow trout population, which was reduced by 70 to 80 percent during the recent drought.

Seeing an opportunity to restore habitat to this waterway, South Coast Region fisheries biologists came up with a plan to place suitable materials into Sweetwater for the rainbow trout to use for new spawning grounds. Beginning on March 20, CDFW Environmental Scientist Russell Barabe, scientific aids Joseph Stanovich and Ken Sankary and volunteer Mark Berlin worked in the hot sun and dry conditions to rehab the streambed. Using a nearby dry stream channel, the team shoveled hundreds of pounds of rocks and materials through mesh screens to remove fine sediment and sand and clean the rock, called cobbles, to make them ready for placement into Sweetwater River. All the rock had to be moved one bucket at a time and poured into pool tailouts (the downstream end of a pool where the water gradually shallows) to create spawning beds about three feet square for rainbow trout.

Though similar work has been done in northern California – specifically two larger-scale projects in the American and Sacramento rivers, which served as the inspiration for this project – it had never been done in this small a stream before.

This small but important project could increase the spawning success of a drought-reduced population in a stream with easy public access. If successful, this project could be used as a model for future habitat restoration activities in other small trout streams. The fisheries team’s work is an example of how our scientists put the mission of CDFW – to conserve California’s fish and wildlife resources for the use and enjoyment of the public – into action.

CDFW Photos. Top Photo: CDFW Scientists hauling buckets of rocks to create spawning beds for rainbow trout.

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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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