ST. GEORGE — Despite its small size, the young tortoise doesn’t escape the eagle-eyed raven’s notice. The large black bird swoops in, sharp beak at the ready with talons extended and gets a mouth full of … plastic?

The Red Cliff Desert Reserve is using 3D-printed “techno tortoises” as part of its effort to track raven predation and potentially mitigate the risk to juvenile tortoises.

Juvenile Mojave desert tortoises are vulnerable to predation and ravens are a high-ranking threat to the reptiles range-wide, Mike Schijf, a biologist for the reserve told the Habitat Conservation Advisory Committee.

Because of this, the reserve has been studying the birds since 2015 as part of its raven monitoring program and has observed predation each year since, he said.

“There is possibly a larger threat to local tortoise populations than what is currently known,” Schijf said.

Ravens thrive near human populations due to “subsidies” such as landfills, artificial reservoirs and power lines, which benefit ravens, and Schijf said their numbers may grow as Washington County does.

Previously the reserve focused on raven nest and power line surveys, finding 53 nests in total and 20 unique nesting territories inside or adjacent to Red Cliffs Desert Reserve. Additionally, two predation attempts and approximately 40 carcasses attributed to ravens were observed, with nearly 50% found in the Ivins/Toe Trail area.

After receiving feedback from the U.S. Fish and Wildlife Service and local partners, Schijf said it was important to collect more data on population densities and predation rates before implementing raven-reduction measures.

The reserve worked with Kerry Holcomb from the USFWS to analyze the results.

To measure population density, the reserve conducted point count surveys across 108 sites between April 8 and May 18, 2022, over approximately 176,000 acres, with a 2-kilometer buffer between each point, Schijf said. Survey sites overlapped tortoise habitat and each survey lasted about 10 minutes.

Surveys were conducted by reserve staff, Bureau of Land Management biologists and interns, and volunteers from the Habitat Conservation Plan and Friends of Snow Canyon, Schijf said.

Ravens were observed at 42 sites — approximately 39% of the total sites, he added.

There were approximately 2.7 ravens per square kilometer, which exceeds the suggested maximum target density of 0.89 ravens per square kilometer to avoid raven-tortoise conflict. Raven observations were generally higher outside the reserve, and highest in the Warner Valley and Sand Mountain areas, Schijf said.

To measure predation rates, 23 decoy stations were set up between April 13 and June 19, 2022, across the point count survey sites — 21 one these hosted a decoy techno tortoise. The final two points served as control sites; one was set up with no decoy and the other with a random juvenile tortoise-sized object.

The 75-millimeter techno tortoises are lifelike, 3D-printed juvenile tortoises produced by Hardshell Labs in Joshua Tree, California, Schijf said.

“They’re pretty lifelike,” he said.

Ravens attacked the decoys 10 separate times at five of the 23 sites, Schijf said. The two sites that boasted the most attacks were at opposite sides of the county — one near Virgin and one west of Zone Six and south of White Hills.

An “attack” was defined as anytime ravens were captured investigating the decoys, Schijf said.

“If it’s not attacking, it’s probably realizing it’s not a real tortoise at that point,” he said. “We can imagine that if it was a real tortoise, it was probably going to be attacked.”

Holcomb estimated that there is an 18.4% annual chance of attack for Washington County’s juvenile tortoises, which is “well above” the suggested threshold of 7.8% for sustainable conflict level, Schijf said. The statistics presented were for 0 to 10-year-old tortoises.

Schijf said the data indicates that tortoise-raven conflicts are unsustainably high in the Upper Virgin River area and that there is a potential risk of “localized to widespread functional; extinction.”

Additionally, any juvenile tortoise within 2 kilometers of a raven’s nest is at risk for predation, but the “problem appears to be more severe outside of the reserve,” he said.

“Ravens are a native species,” Schijf said. “Some level of predation is expected, but there does come a point, that a native species can actually become invasive if its population explodes to a certain degree. And it’s looking like that may be what we’re seeing.”

Because the results appear to indicate a need for management solutions, Holcomb is expected to offer suggestions and further analysis to the Habitat Conservation Advisory Committee as early as March, Schijf said. But the timeframe has not yet been set.

Ivins City Mayor Chris Hart expressed frustration about the length of time it has taken to implement solutions.

“We’re great at doing surveys,” he said. “We’re great at diagnosing the problem. We’re terrible at actually doing something about it. Here we’ve gone on — it’s been at least five years we’ve been discussing this and taking subsequent actions — each one takes another year. And my question is: How many tortoises have we lost in that five years?”

One potential complication in mitigating raven predation is that the birds are protected under 1918’s Migratory Bird Treaty Act, which prohibits the killing, capturing, selling, trading, and transporting of protected migratory bird species unless authorized by the USFWS.

Schijf said that the reserve is working toward obtaining any federal and state permits required to implement depredation measures.

Various raven-control strategies have been considered, such as egg oiling, St. George News previously reported. The practice involves covering raven eggs with vegetable oil to suffocate the embryos inside and is considered a humane way to control bird populations.

Additionally, egg oiling could potentially trick ravens that typically prey on juvenile tortoises into believing the area isn’t viable for egg-laying, the article reads.

To learn more about the surveys, view Schijf’s presentation. To learn more about the Red Cliffs Desert Reserve, visit its website.

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