MOJAVE NATIONAL PRESERVE, Calif. –A few hours had passed since we left a sandy trail winding up the north flank of Clark Mountain and trudged up a steep slope of broken rock, flowering cactuses and creosote bushes, pinyon pine, and juniper. By early afternoon the sky was getting dark as thunderclouds closed in.

It was late May, and I was tagging along with Lori Hargrove, an ecologist with the San Diego Natural History Museum and part of a team of researchers. They were retracing the steps of scientists who 79 years ago had surveyed birds, small mammals, and their habitats at Clark Mountain in southeast California.

Hargrove, who specializes in bird monitoring and ecological analyses, had wanted to scout a route to a forest of white fir trees hugging treacherous terrain near the 7,933-foot summit. Detailed field notes from scientists there in the late 1930s told of at least one researcher who had hiked up and over the summit, joining companions at their 6,100-foot campsite on the south side of the mountain. But we couldn’t see a way up, not that day.

The fir forest at Clark Mountain contains what biologists call a “sky island” – a habitat defined both by its high-altitude biodiversity and physical isolation from the expansive desert below (also see here and here). It’s also where birds and small mammals may help tell the story of climate change’s impact on California’s wildlife.

“In ’39, they spent only one night trapping in the fir forest,” Hargrove said. “If we can spend a whole week, maybe we’ll have new discoveries.”

Retracing the steps of 20th century biologists

The work at Clark Mountain is part of the Grinnell Resurvey, a research project launched in 2003 to cover the same transects across California that U.C.-Berkeley zoologist Joseph Grinnell and his colleagues had surveyed a century ago.

Between 1904 and 1945, biological surveys had been completed of the Mt. Lassen area in the northern Sierra Nevada; coastal regions north of San Francisco; Yosemite in the central Sierra; Kings Canyon and Sequoia national parks in the southern Sierra; and the state’s deserts including Joshua Tree, Death Valley and Mojave. Resurvey work in California’s deserts marks some of the last phases of the entire Grinnell Resurvey.

During those early decades of the 20th century, Grinnell and his team documented and collected mammals, birds, amphibians, and reptiles from more than 700 locations throughout California. In all, the Grinnell survey amassed more than 100,000 specimens, 74,000 pages of meticulously detailed field notes, and 10,000 photographs.

Grinnell, the founding director of the Museum of Vertebrate Zoology at Berkeley widely considered a pioneer of modern ecology, knew that his early 20th century survey would help future biologists better understand the impact of a rapidly growing California, its changing land use, and loss of natural habitats.

“This is a guy who was writing in 1910 and recognizing that things were changing,” said Steven R. Beissinger, a professor of conservation biology and wildlife ecology at Berkeley who has led the Grinnell Resurvey around the state. As Grinnell and his colleagues collected specimens and built their museum at Berkeley, Beissinger said, they knew they were also establishing a baseline scientific record of wildlife in California. Grinnell personally wrote in 1910 that the full value of the survey would not “be realized until the lapse of many years, possibly a century.” For many years, Grinnell’s quote hung on the museum wall at Berkeley to inspire students, Beissinger said.

The Grinnell Resurvey

The Grinnell Resurvey has been a collaborative effort by Berkeley, the San Diego Natural History Museum where Hargrove and scientist Philip Unitt work, U.C.-Santa Cruz, the University of New Mexico, and the National Park Service. Grants secured in 2015 from the National Science Foundation and the National Geographic Society are funding the final phase of the resurvey in California’s deserts.

Warmer temperatures in California deserts, the greater American Southwest, Australia and other arid regions are already pushing many tortoises, lizards, birds and other animals to their physiological limits, researchers have found.

On August 6, the Grinnell Resurvey published a paper on a widespread crash in the number of bird species throughout the Mojave Desert. The study, in the Proceedings of the National Academy of Sciences (PNAS), was based on a resurvey of 61 sites across the desert that Grinnell and his team first surveyed in the early 20th century.

Beissinger and his colleague Kelly J. Iknayan found that on average, the 61 sites had lost 43 percent of the bird species seen there a century ago. “Climate change, particularly decline in rainfall, was the most important driver of avian community dynamics in the Mojave Desert,” they wrote. Sites that had received less rain in recent decades, compared with the early 20th century, had a higher probability of local extinctions, they added. Most of the 61 sites became drier over the past century, receiving up to 20 percent less precipitation.

“The harsh nature of desert environments makes them more likely to become less suitable for life and offers a prescient warning for biodiversity loss as future climates are pushed further toward extremes,” Iknayan and Beissinger wrote. (For more on this new study, see coverage from KQED public radio and Smithsonian magazine.)

In Joshua Tree National Park, previous survey work has found that excessive heat and drought has caused a die-off of pinyon pine and juniper trees, and a subsequent crash in populations of chipmunk and black-chinned sparrow, said Philip Unitt, Curator at the San Diego Natural History Museum and a specialist in subspecies identification of California birds. Unitt also was a leading member of the team at Clark Mountain.

Resurvey work in Yosemite, begun in the mid-2000s, has revealed shifts in animal populations as a result of warmer temperatures. A 2008 study based on a resurvey of wildlife in Yosemite at 3,000 meters (9,842 feet) found that half of the 28 animal species examined had expanded their range upslope about 500 meters (1,640 feet) – a shift consistent with a documented rise of about 3 degrees C (5.4 degrees F) in average minimum temperatures at that elevation in Yosemite over the past century.

Another study in 2013, also written by Beissinger, found an overall decline in the biodiversity of bird species over the past 80-100 years in the Sierra Nevada.

A complicated picture for California’s deserts

Climate change, of course, is not the only factor affecting the health, distribution, and movement of wildlife in California – including the state’s deserts. Just because it’s getting warmer doesn’t mean all species are packing up and moving north, or upslope. The impacts of climate change in California’s deserts are especially difficult to disentangle from other changes.

One reason is that development in urban areas of California has been good in many respects for birds and small mammals. Many bird species have thrived in suburban neighborhoods landscaped with trees, shrubs, flowers, bird feeders and other sources of food. Small mammals also have prospered. Hargrove and her colleagues call these animals “urban adaptors.”

Some coastal species, including the American Robin Anna’s Hummingbird, and Raven, have done so well in urban regions of California that they’ve expanded their historic range into remaining wilderness areas far inland. There’s evidence that these range expansions of urban adaptors have displaced other species in wilderness areas.

Another factor complicating the climate change picture has to do with wildfire, Hargrove said. For example, some bird species the biologists have seen in recent years in the San Jacinto Mountains in Riverside County have migrated there from points north over the past century. Displaced by wildfire, they’ve expanded their range southward – not northward, as one would expect in a warming world.

Why the San Jacintos? Because the mountain range had not experienced a major wildfire like those repeatedly seen during the 20th and early 21st centuries in the San Bernardino Mountains and the Southern Sierra Nevada (that is, until a fire ignited by a suspected arsonist this past July charred thousands of acres near Idyllwild in the mountain range). And so the observed changes in geographic ranges have been exactly the opposite of what scientists would expect in a warming world – when no other factors are at play.

Unitt also sees wildfire, which has wreaked havoc up and down the state this summer, as a huge driver of species dislocation. At San Gorgonio Pass, a gap on the rim of the Great Basin between the San Bernardino Mountains to the north and the San Jacinto Mountains to the south, numerous bird species have retracted their ranges because the area has burned so frequently, Unitt said. “These species have not been able to re-establish themselves, so they’re moving upslope as a result,” he said.

Setting up camp

Back at Clark Mountain, the small group of scientists in May set up a base camp on its southern slope at about 6,100 feet. Believed to be the same site used by Grinnell’s team eight decades ago, the primitive site appeared little improved since their day in the late 1930s. A few picnic tables, an old barbecue, and a few fire pits marked the site. Shotgun shells littered the area, a sign that researchers are not the only ones who venture there.

During breaks between survey trips, Hargrove and her colleagues flipped through a thick binder that Hargrove had prepared, full of copies of field notes prepared by Grinnell team biologists back in the 1930s. In May of 1939, the Grinnell team wrote of hiking to a snow bank on the mountain.

In high desert habitats like those found at Clark Mountain, the availability of water is extremely important to the survival of wildlife already living on the edge, Clark says. “Everybody knows that, but maybe it’s still under-appreciated. A lot of springs have dried up, and those are the sites that we see the strongest changes in composition of birds present.”

In the San Jacinto Mountains, biologists with the original Grinnell Survey had written of frequent encounters with a bird called the Bell’s Vireo, a bird that thrives in riparian habitats, Hargrove said. “They like to be near water, and that’s one of the species we found strongly declined at many of our sites because now there’s no longer riparian habitat at a lot of sites and less water,” she said.

Other things have been slow to change. At Clark Mountain, some of the biologists said they were surprised to find very few invasive species of grasses and other vegetation; the rugged high desert habitats of Clark Mountain were much the same as in Grinnell’s day. That was a bit surprising to hear. At our camp, modern civilization never seemed that far off; you could hear the drone of cars and trucks on Interstate 15, and all day long jetliners passed over Clark Mountain on their way toward Las Vegas 60 miles to the northeast.

Those who pay attention can see that Clark Mountain is brimming with wildlife, from bighorn sheep and black-tailed jackrabbits to kangaroo rats, pinyon and deer mice, and other small mammals. And everywhere you can hear the chirping of birds – Juniper Titmouse, Black-chinned Sparrow, Black-throated Sparrow, Rufous-crowned Sparrow, Gray Vireo, Wilson’s Warbler, Western Tanager, Warbling Vireo, Bushtits, Anna’s Hummingbirds, and many more.

Hargrove has had a special interest in the Black-throated Sparrow, a desert bird that lives in a variety of dry open habitats. “If it’s getting hotter and drier we’re going to be having longer droughts, (and) then that desert habitat that they prefer may become unsuitable,” Hargrove says. “So we’ll have to see what happens. Are they going to adapt, or move, or become more rare?”

Joining Hargrove and Unitt in late May were half a dozen other researchers, among them Scott Tremor, a small mammal specialist with the museum who led the trapping of small mammals, primarily rats and mice. Also joining the group was Howard Thomas, a retired professor from Fitchburg State University in Massachusetts who for a decade has enjoyed joining the San Diego biologists on their field expeditions. In his retirement, Thomas also has traveled to Kenya, where he’s working with a former graduate student to compile an atlas of small mammals in the East African country.

As the global climate continues to warm and wildlife finds it increasingly challenging to make a living, biological surveys like the Grinnell Resurvey will help government agencies, and the courts, decide what habitats should be protected, Thomas said.

“By going out and sampling these things periodically, over a hundred years or so, we’re able to get a temporal sense of how a species exists out here,” Thomas said. “And, in order to be able to document this in court, in land court or anyplace else, you need voucher specimens. These are actual pieces of evidence that are used by the law to decide whether the land should be protected or modified (in) use. So without them, we really don’t know what we’re doing.”

Back on the north slope of Clark Mountain, as Hargrove peered through her binoculars at the high-elevation fir forest, she set her sights on next year’s return to Clark Mountain and finding a route to Clark Mountain’s highest sky island habitats.

There, she and her colleagues hope to find the wildlife that make it their home – and uncover more clues to how climate change is affecting wildlife across California.

More to read

Studies:

* Grinnell Resurvey studies and reports
* Southern California desert habitats: Climate change vulnerability assessment summary
* Climate change effects on southern California deserts
* Desert-adapted species are vulnerable to climate change: Insights from the warmest region on Earth

News stories:

* California’s birds are testing new survival tactics on a vast scale. Retracing the steps of a century-old wildlife survey, ecologists find that birds are making remarkable adaptations to climate change.
* In California, climate change is an ‘immediate and escalating’ threat
* The Cal EPA report referenced in the news story above.
* Climate scientists see alarming new threat to California
* Climate change may be as hard on lizards as on polar bears
* The California desert is dying, and people seem to think that’s ok
* How climate change is affecting the desert landscape
* Struggle for survival: Some animals moving, vanishing as deserts grow hotter
* What climate change will mean for the California desert

More:

* Across a century of change, the gift of a baseline
* 2017 TED Talk by Steve Beissinger on the Grinnell Resurvey near the California/Oregon border
* A backpacker’s account of summitting Clark Mountain:
* Mammals, Mojave National Preserve, National Park Service
* Birds and climate change, Joshua Tree National Park, National Park Service