Across a Century of Change, the Gift of a Baseline

For an ecologist, Sarah MacLean has found herself in some unlikely places over the past three summers. Binoculars in hand, she has navigated highway overpasses and garbage-littered lots, prowled suburban streets around Los Angeles, and explored farmers’ yards in the Central Valley. 

Wherever she went, MacLean maintained the same daily routine. Starting before dawn, she would make her way along a predetermined route, stopping at 10 fixed points. For seven minutes she’d count every single bird she could see or hear. “In some places, there’d just be one house finch. In other places, I couldn’t write fast enough, so I kept a mental list and caught up when they all stopped flying by.”

A graduate student in the Department of Environmental Science, Policy, and Management (ESPM), MacLean is part of a community of scientists who are retracing the steps of Joseph Grinnell, the pioneering naturalist and founding director of UC Berkeley’s Museum of Vertebrate Zoology (MVZ). They’re searching for insights into how a century of change—both in the climate and in the way humans use the land—has affected the biodiversity of California. Between 1904 and 1940, Grinnell and his colleagues surveyed birds, mammals, reptiles, and amphibians across the state’s length and breadth, from Mount Lassen to Death Valley to the hills above his native Pasadena. They brought back more than 100,000 specimens and filled more than 74,000 pages of field notes with detailed counts and descriptions of every creature they came across. 

Their efforts yielded a trove of information for future scientists, just as its primary author intended. Steve Beissinger, an ESPM professor of conservation biology, has led the 15-year-long project of resurveying Grinnell’s sites throughout the state. This work has been made possible entirely by the rich archive of data housed in the MVZ. 

Grinnell’s efforts were largely motivated by the human encroachment into wildlife habitat that he was already witnessing. In a 1910 article in Science, he described what he believed would prove to be the greatest value of his museum. “This value will not, however, be realized until the lapse of many years, possibly a century, assuming that our material is safely preserved. And this [value] is that the student of the future will have access to the original record of faunal conditions in California and the west, wherever we now work.” 

That quote, which has long hung on the wall of the MVZ, inspired the resurvey. “Grinnell definitely had a sense that he was giving us a record of what California was like in the early 1900s,” Beissinger says. “He gave us the gift of a baseline.”

To make full use of that gift, contemporary researchers had to do some detective work to retrace Grinnell’s steps. Fortunately, his specimens provided key clues. They searched the museum’s public database to find out where and when certain specimens were collected, then cross-referenced that information with descriptions in the field notes. Grinnell often made annotated maps, but not all of his students were as exacting. 

“Sometimes they’d say, ‘We walked the Yosemite Falls Trail,’ and you’d know exactly where to go,” Beissinger says. “Sometimes it would just say, ‘Horse Mountain.’ Well, there are three Horse Mountains in California. So you’d have to look at the verbal description to figure it out.”

Having spent so much time buried in Grinnell’s notes, Beissinger has developed a sense of the man. “He was very much a workaholic,” he says. “He would go on vacation with his wife and still be writing field notes. God only knows what he would have done if he had a computer.” 

Grinnell’s philosophy was simple: Record as many sights and sounds as possible. That included seemingly ancillary details, such as weather conditions and vegetation types. 

“He never traveled one inch but what he had that notebook open,” recalled the late Ward Russell in a 1992 interview. Russell served as the MVZ’s preparator for 40 years, gathering specimens with Grinnell all over the state. “He said over and over, ‘Put it all down! You may not think it’s important, but somebody may.’” 

An excerpt from Grinnell’s notes from May 5, 1907, in Glendora shows that philosophy in action. He jots down everything he notices in an extremely detailed narrative: the types of bushes birds alight on, the swoops and swerves of their mating performances, the exact interval in seconds of a male valley quail’s hollering call and a lazuli bunting’s “hurried shrill song from the top of an oak.” 

More than a century later, the picture of change captured by the resurvey is both sobering and complex, even as Grinnell’s methods have proved, in a sense, to be timeless. Resurvey participants have replicated his omnivorous approach to information gathering. “The Grinnellian method is the gold standard,” MacLean says, “so we’ve tried to emulate that note-taking style.” But they’ve also updated it, incorporating modern data-collection methods.

Beissinger, MacLean, and their colleagues have also benefited from the use of new, sophisticated statistical methods called occupancy models, which allow them to account for improvements in modern researchers’ observational capabilities relative to Grinnell’s. “He was an amazing naturalist, but technology has progressed,” MacLean notes. “We have better, clearer binoculars. I’m out there with my smartphone. If I hear an unfamiliar birdcall, I can use an app to identify it.” These aids increase the likelihood of their detecting birds; the models help them establish the probability of detecting a species independent of the probability that the species is actually there (technically known as “occupancy”). 

While the resurvey has examined the occupancy of both birds and small mammals in every eco-region of California, the most recent wave of findings to emerge from the project has to do with how the avian species of the deserts and the Central Valley have fared since Grinnell’s day.  

Kelly Iknayan, another ESPM PhD student in Beissinger’s lab, has led the resurvey of birds in the Great Basin and Mojave Deserts. Where Grinnell maneuvered his Ford Model T, Iknayan drove a Ford Explorer. In addition to the field notebooks that she compiled using Grinnell’s exacting standard, she lugged around 75 pounds’ worth of audio-recording equipment. “We have a record of anything singing at these sites,” she says. “That’s 10 terabytes of data that offers ample opportunities to anyone looking at it in the future.” And with a GPS unit, she digitized the precise coordinates of her survey locations, to assist future researchers retracing her steps.

While most of those desert sites have been relatively undisturbed by development, climate change is already making inroads—especially in the Mojave. “Across the board,” Iknayan says, “bird species are declining.” The result is a collapse of the entire bird community, to a new baseline with fewer species per site. At all but 3 of her 61 sites, Iknayan recorded a significant decline in the number of species found. And of 135 breeding species she surveyed, all but 3 showed a negative trend in occupancy compared with that observed by Grinnell and his team. The only bird that has increased in numbers is the common raven, which famously thrives on disturbance. 

Changes in precipitation best explain these declines for desert birds. With climate change likely to increase the frequency of heat waves, the outlook is grim for native birds of the Mojave. “Projections show many more days in the future when birds could experience lethal heat and dehydration,” Iknayan says.

Creatures in California’s other ecosystems are coping with these compounding changes in complex ways, but a common thread is emerging from the data. In this arid state, where water has long preoccupied people, early findings suggest it’s a dominant story for the resident birds and mammals, too. 

“Water is emerging as a key variable in how species are shifting their geographic range in relation to climate change,” says Beissinger. “One of the things we learned from our resurvey work in the Sierras was that temperature change and precipitation change can act as opposing forces.” Half of the 28 small mammal species resurveyed in Yosemite National Park have shifted their range upward, in response to warming temperatures. But as Yosemite is drying out and warming, climate change is making other places rainier. On Mount Lassen, for example, wetter conditions have resulted in many species moving downslope. Even in Yosemite, other species have moved downward, a sign that certain mammals might be responding more strongly to changes in precipitation than to rising temperatures. 

MacLean also found that water availability was the most important factor determining birds’ distributions in the Central Valley. “We saw a minimal effect of urbanization and agriculture in determining occupancy, which is surprising because the Central Valley is a hugely modified landscape. Water mainly exists where people allow it to, and where there’s water, there is greater richness of bird species.” 

In the Los Angeles Basin, however, the effects of urbanization have been more alarming. Some birds that were ubiquitous in Grinnell’s time, such as the house finch, are still around in huge numbers today. But others that were common characters in his notes, such as the yellow-breasted chat, are now almost completely missing. Exotics like red-crowned parrots, red-whiskered bulbuls from India, and peacocks proliferate instead. 

These changes have less to do with water and more to do with human tastes. Whereas many birds native to the Central Valley can still find habitats in native trees like cottonwoods and sycamores, around farmhouses and parks, the native birds of LA have seen their familiar roosts replaced by exotic trees such as date palms and magnolias. “This loss of a very diverse native bird community in LA is startling,” MacLean says, “because it’s such a hot spot for biodiversity.”

It’s impossible to predict what the “students of the future” will find when they resurvey California a century from now—or sooner. “I’m hoping they come back in 25 or 30 years, when climate change has really kicked in,” Beissinger says. Whenever they do, like his forerunner, he has a message for them. “Make sure you’re collecting data in a way that the next generation will be able to use it beyond your specific study,” he says. 

He thinks that Grinnell’s approach to close observation will always be relevant to ecological research, even in the age of remote sensing and sophisticated spatial-mapping software. “Capture as much on-the-ground information as you can, and make sure to preserve it,” he adds. “With Grinnell’s data, it was like we were taking the field trip with him.” 

As she trekked through dramatically transformed landscapes, furiously taking notes, MacLean was ever mindful that she was collaborating with colleagues across eras, contributing to a collective effort to understand subtle but momentous shifts happening in the natural world. 

“Our main goal is to collect as much as we can and far more than we need for our current projects,” she says. “It’s a challenge, because we don’t know what people are going to need in the future, what questions they’ll be asking, what technology they’ll have at their disposal, what statistical methods they’ll develop. Grinnell was in the same place we are—he just knew it was important to create as robust a baseline as he could. We’re trying to mirror that, and hope it will be as much as they need.”

In the meantime, Berkeley’s new Institute for Parks, People, and Biodiversity will help draw lessons from the resurvey’s findings for park managers and wildlife conservation planners working to identify and connect “refugia”—places that are buffered from the effects of climate change, where unique physical or ecological conditions help species persist. 

Grinnell trained many of the first scientists who conducted pioneering research in the national parks. Today, his gift of a baseline is enabling their successors to understand how different species are managing in the face of climate change—and to help those species adapt and survive. It’s a legacy that even Grinnell could not have foreseen, but one he’d likely applaud.