• Steve Brown

New findings indicate Mojave bird populations have dropped by half over past century

Juvenile Cooper's hawks
Juvenile Cooper's hawks

Scientists from the University of California, Berkeley have resurveyed sites throughout the Mojave Desert from the Grinnell survey done during the early part of the 20th century. What they have found is disturbing.

Joseph Grinnell, founding director of the Museum of Vertebrate Zoology and Annie Alexander, the Hawaiian sugar heiress who endowed the museum and selected Grinnell as director, realized California was changing rapidly. Grinnell, his students, and Alexander became motivated to conduct inventories of terrestrial vertebrates throughout California and the west.

MVZ Party, 1938: Elmer Aldrich, Dale Avery, Dave Johnson, Tom Rodgers, J. Grinnell.  Photo courtesy of The Grinnell Resurvey Project.
MVZ Party, 1938: Elmer Aldrich, Dale Avery, Dave Johnson, Tom Rodgers, J. Grinnell. Photo courtesy of The Grinnell Resurvey Project.

Between 1904 and 1940, they documented and collected mammals, birds, amphibians, and reptiles from more than 700 locations. Their efforts resulted in a snapshot of early 20th century vertebrate diversity that includes more than 100,000 specimens, 74,000 pages of field notes, including bird count data and habitat descriptions, as well as 10,000 images. The data collected has been referred to as a "potential gold mine for investigations of species' responses to climate change, change in human land use, and other stressors."

Around a century later, museum faculty, students, and collaborators have been resurveying the sites covered in the Grinnell survey to assess how terrestrial vertebrates have responded to environmental change and to establish a contemporary benchmark for future comparisons.

Scientific American documented the Grinnell resurvey project in the Mojave Desert in 2017, noting that while the responses to increasing warmer, drier conditions vary among species, the trend does not bode well overall for desert wildlife. Steve Bessinger, a conservation biologist at UC Berkeley noted in the article that of 135 bird species surveyed at the time in the Mojave, only the common raven has significantly expanded its range since the early 20th century. Ranges of 38 other species have contracted.

The Grinnell resurvey showed that 62 sites in the Mojave lost on average 43 percent of their bird species, while 39 of the 135 breeding bird species studied in the initial survey were less likely to be found at a given site now than compared to a century ago, according to a story in Smithsonian.

It's not just increasing heat that is likely to be the problem, but rainfall. According to information about the resurvey in Smithsonian, rainfall at survey sites receive 20 percent less precipitation than at the time of the initial survey. This decline in precipitation results in less surface water and an impact on plants that birds rely upon for sustenance and hydration.

As desert birds seek food and water at higher elevations, they face a challenge as those areas are also drying. Research from the resurvey also noted no new bird species are replacing those lost in the Mojave.

“The deserts are in trouble,” Beissinger warns in the Smithsonian story, “and outside of the Arctic, they’re probably the next hot spot for climate change.”

According to the Smithsonian story, national parks and preserves weren't immune to the precipitous decline in bird populations. Some of the largest declines were found in Death Valley National Park.

The Grinnell resurvey of the Mojave Desert may show us that bird populations are the proverbial "canary in the coal mine." No parts of the desert are immune to the collapse, and projects such as the Cadiz Water Project, which could post a serious threat to the availability of surface water in seeps and springs for wildlife, are serious and unmitigable dangers to the future of biodiversity in the Mojave Desert. Utility scale renewable energy projects threaten bird populations as well, with solar projects like Ivanpah killing thousands of birds per year.

The Grinnell Resurvey Project

68 views0 comments

Recent Posts

See All