ST. GEORGE — Despite Southern Utah’s dry summer and extreme heat, biologists say the region’s tortoises appear to be doing OK.
Mojave desert tortoises are listed as threatened under the Endangered Species Act and habitat throughout Washington County has been set aside for their protection in the form of the Red Cliffs Desert Reserve.
Population numbers inside the reserve and Red Cliffs National Conservation Area have been stable since about 2007 to 2009, said Adam Kavalunas, the Utah Division of Wildlife Resources’ Southern Region outreach manager, via email.
“There is no evidence of recent declines in tortoise densities,” he wrote. “We are having an unusually hot summer, but tortoises have evolved strategies to tolerate periods of intense heat. In the summer, tortoises aestivate (meaning they will retreat into a deep shelter and be inactive, often for weeks) so that they can survive these very hot and dry periods.”
Red Cliffs Desert Reserve biologist Mike Schijf said tortoise monitoring isn’t planned for this year. But while the region has been hot and dry, it’s unlikely to be a “major concern” unless it is prolonged.
“If we get some monsoon rains, there should be some decent tortoise forage later this year,” he said. “However, the most important season for precipitation is winter, which ensures tortoises have food when they emerge from their burrows during springtime.”
Surveying tortoises
The division has been monitoring tortoises in the reserve since the late 1990s to “understand long-term population trends and assess the overall health of populations in Washington County,” Kavalunas said, adding that this information helps biologists determine if a population is vulnerable.
The most recent survey was last year and conditions were considered “ideal,” Kavalunas said. Record-high precipitation and lower temperatures encouraged plant growth – a boon for desert tortoises.
“During the 2023 surveys, tortoises appeared healthy, with green around their mouths, indicating that they had recently eaten,” he said. “We attribute the low annual adult mortality rate to an ideal spring, with lots of plant growth and plenty of food available for tortoises.”
During field surveys, the DWR conducts health assessments for each tortoise staff encounter, checking for signs of upper respiratory tract disease – a bacterial infection. Surveyors also check for nasal discharge, mouth abscesses and overall shell health. They assess whether they’ve been captured before and when by looking for indicators previous staff may have left on the shell, like file marks.
The survey was conducted from April 3 to June 13, 2023, and 178 tortoises were observed, most of which appeared healthy. There were about 20.7 tortoises per square kilometer in three areas of the reserve, according to a survey report written by the DWR’s Ann McLuckie, Richard Fridell and Tyson Victor.
Approximately 9% showed signs of upper respiratory disease and six had burn injuries. Surveyors calculated a 1.4% annual mortality rate, which the report states is the “lowest recorded mortality since monitoring was initiated in 1998.”
Schijf said the population densities recorded during the survey were the highest since 2005.
“While we don’t want to put too much weight into any single year of data, those findings indicate that the Reserve population is doing quite well, and that the large wildfires from 2020 may not be having as much of an impact on the population as we had previously feared,” he said.
At the July Washington County Habitat Conservation Advisory Committee meeting, St. George resident Richard Spotts spoke during the public comment period, asking, “Is the glass half-full or half-empty from the tortoise conservation perspective?”
According to a report issued by Conserve Southwest Utah, the Upper Virgin River Recovery Unit, which includes Washington County, has the densest tortoise population in the range. However, the number of tortoises per kilometer in the reserve declined by nearly 40% between 1999 and 2023, with an annual mortality rate of 3.2% from 2004 to 2014, with a “slight recovery” between 2015 and 2023.
This recovery is “not to a level that matches density observed pre-2007,” the document states. “Rangewide, there were an estimated 336,393 adult tortoises in 2004 and 212,343 in 2014, representing a decline of 124,050 (-37%) over this 10-year period. Within Red Cliffs Reserve, the estimated abundance of adult tortoises declined from an estimated 3,482 in 1999 to an estimated 2,425 in 2023, an estimated loss of 1,057 (-30%).”
Spotts said the county could lose its tortoise population in less than 35 years if this trend holds.
“And I’m 72, so three and a half decades, actually, it just doesn’t seem that long a period,” he said. “So, I guess from my standpoint, we’re doing a lot of great things, but the question is, ‘How can we stop and then reverse the decline in this recovery unit, which is probably the key recovery unit for the tortoise range?'”
The Red Cliffs Desert Reserve’s administrator, Cameron Rognan, said the higher percentage is a long-term rate that includes periods of drought, which were responsible for much of the species’ decline in the area. But reiterated that recent surveys have found lower mortality rates.
“If we can, you know, have a trend where we can avoid these long-term droughts, I think tortoises are actually recovering right now,” he said. “It just takes them a long time – they’re a long-lived species, and it takes them a long time to recover.”
Reducing threats to the species
Kavalunas said the division expects tortoise populations to be stable going forward, barring “significant random events.”
Additionally, the species could be rebounding, Schijf said, adding that whether this continues depends on various factors, such as drought, wildfire and disease. Still, the reserve is “optimistic” about the future.
“If we can effectively protect unburned habitat, limit the overall impact of wildfires, reduce or mitigate habitat fragmentation, and minimize the impact of predation, then there is continued reason for optimism that local tortoise populations will remain stable,” he said.
Washington County’s tortoises appear to do well in Snow Canyon State Park, particularly on the park’s south side, where the DWR observed some of the highest densities in the reserve, Kavalunas said. The reptiles also appear to do well in Zone 6 – nearly 7,000 acres of land located west of Bloomington.
Much of this land features unburned habitat, where tortoises appear to fare better and the highest densities are typically found. Intact ecosystems boast higher plant diversity and fewer invasive species, Schijf said. Habitat loss is often considered the “largest threat” to the species locally, particularly as the result of wildfires.
Additionally, Kavalunas said the reptiles have done well in areas where they’ve been translocated from parcels slated for development.
“We have translocated over 500 displaced tortoises taken from developed areas around the County and placed them in a designated area in the Reserve,” he wrote. “The tortoise population in this area has increased in density the last few years, and there have been observations of hatchlings, indicating successful reproduction.”
Tortoises struggle in areas “dominated by nonnative plants,” such as cheatgrass, and where their habitat has been degraded, Kavalunas said.
“Tortoises have high site fidelity, meaning that they will stay in an area that they are familiar with even though it might be poor quality with few food choices,” he said. “So it is important for us to actively improve and restore critical habitat.”
The DWR completed several surveys to better understand the impacts of nonnative plants on tortoise habitat in the reserve and conservation area, finding some invasive species present across the region, such as cheatgrass and red brome, and others that have expanded their reach, like Sahara mustard plants.
“Their presence has been attributed to an increase in the size and spread of wildfires across the West. … We continue to work with our habitat biologists and our agency partners to address the control of these exotic, invasive plants and implement projects to restore habitat for tortoises and other wildlife in the area, which is an ongoing challenge.” Kavalunas said.
Schijf said tortoises that must eat nonnative plants due to less native forage being available may experience health issues that “negatively impact their body condition, increase susceptibility to disease, and reduce resiliency to stressful environmental events.”
Habitat fragmentation can also put the species at risk by reducing gene flow.
“This can present many problems, especially over a long time horizon,” Schijf said. “Generally speaking, a tortoise population will be healthier if it is more genetically diverse. Without thoughtful design, roads and other projects bisecting tortoise habitat may impede the ability of a tortoise to reach neighboring habitat (and neighboring tortoises).”
The Habitat Conservation Plan, which oversees the reserve, has been monitoring culverts and underpasses on Red Hills Parkway with game cameras since 2022 to document how often tortoises use them, he added.
“Last year alone, at least 66 individual tortoises used five different culverts, including 31 tortoises that crossed beneath the roadway (plus numerous crossings from other wildlife),” Schijf said. “These findings are important because until recently, the frequency in which tortoises used culverts was widely unknown. This elevates the importance of culverts as mitigation for future roadways, and there are plans to install culverts along existing roadways that currently lack connectivity.”
Additionally, common ravens prey on juvenile tortoises, and recent surveys showed “concerning results” regarding population densities and predation rates, Schijf said. Earlier this year, the U.S. Fish and Wildlife Service issued a permit to Washington County, enabling it to reduce local raven populations using egg oiling, where raven eggs are coated with oil.
“Which is essentially a raven birth control method that does not involve any direct killing of ravens,” he said. “These efforts are expected to continue next year and will be ongoing, along with population surveys to help determine egg oiling effectiveness. Our goal is to reduce raven populations to a threshold where there is no longer a significant risk to juvenile tortoise survivorship.”
Schijf said he feels encouraged by the progress that’s been made to reduce threats to the species.
“We definitely have more management tools available now compared to 7 years ago when I began working in this position,” he said. “I am most encouraged by the strategies we have begun to implement to reduce wildfire impacts, as well as our progress with raven management.
“These efforts have been made possible by collaborating with our local partners, and receiving great input from experts who work elsewhere in the range of the tortoise. There are still plenty of challenges that remain, and plenty of work to be done to protect this species. However, some of these threats facing the tortoise seem less overwhelming when you see progress being made on the ground.”
Photo Gallery
A juvenile tortoise wanders through the Red Cliffs National Conservation Area, June 11, 2016 | Photo courtesy of John Kellam/Bureau of Land Management, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News The Utah Division of Wildlife Resources conducts a survey of Mojave desert tortoises, Washington County, Utah, date not specified | Photo courtesy of the Utah DWR, St. George News
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