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.

Five agencies in two states recently partnered to help a tiny population of Greater Sage Grouse avoid extinction along the California-Nevada border. Biologists from the California Department of Fish and Wildlife, the U.S. Fish and Wildlife Service, Los Angeles Department of Water and Power, the Bureau of Land Management and the U.S. Geological Survey are working together in this first-of-its kind study. On April 22, the bi-state team of scientists captured, inseminated, transported and released 17 of these female upland birds to a new habitat where they will hopefully flourish and repopulate. Eight male birds were also transported to Bodie Hills as part of the study.

The birds were captured near Bodie and moved to Parker Meadows, about 30 miles south. CDFW scientists have been tracking the number of Greater Sage Grouse in Parker Meadows for years, and it was evident that human intervention would be necessary to keep the group alive. Between 2002 and 2010, the number of males had dropped from about 17 to only four, and CDFW estimated that the entire population had a 70 percent chance of going extinct in the next five years.

Translocation was chosen as the best option to save them, as it would not only boost the number of birds in the area, but also immediately widen the gene pool.

The birds were captured at night, measured and radio-collared. The hens were also artificially inseminated with sperm from the males in the Bodie population before being transported and released to integrate into their new home. (Watch video of the capture, insemination and release.)

Although biologists from the U.S. Geological Survey will be doing most of the hands-on work with the birds, CDFW biologists played an important role as well. Environmental Specialist Tim Taylor worked for months to obtain the proper land access permissions and assess the habitat near Bodie. Taylor identified several potential problems (including conifers, where raptors would likely perch while in search of prey, and barbed wire fencing) that needed to be removed prior to the relocation. And Senior Environmental Scientist Scott Gardner, in Sacramento, was instrumental in securing grant funding – without which, this partnership project would not have been possible.

“It’s a long term thing – it’s going to take about five years to get results we are hoping for,” Taylor said. “But we’ve got a great crew and I’m confident we’re going to have success and keep that little population going.”

Read more about the Greater Sage Grouse study.

Photos by Dan Hottle/USFWS