jul18 2023
Tucked away in the stunning landscape of the Crimson Cliffs Desert Get, an unusual battle is unfolding between the cunning raven and the vulnerable juvenile Mojave desert turtle.
Despite its diminutive size, the young turtle is no match for the watchful eyes of the majestic black bird. With its sharp beak and extended talons, the raven swoops down, ready to feast on its prey. But instead of a mouthful of succulent turtle, it encounters something unexpected… plastic. Crimson Cliffs
To tackle the issue of raven predation and potentially mitigate the threat to young turtles, the Crimson Cliffs Desert Get has embarked on an innovative initiative. They are employing 3D-printed “techno turtles” as part of their efforts to map raven predation patterns. Crimson Cliffs
According to Mike Schijf, a biologist for the reserve who advises the Environmental Conservation Advisory Board, ravens pose a significant threat to juvenile turtles throughout their range. The reserve has been studying these birds since 2015 as part of their raven monitoring program and has observed predation every year since then.
Cliffs believes that the danger to native turtle populations is even greater than currently recognized.
Ravens thrive in close proximity to human populations due to human-made attractions like landfills, artificial reservoirs, and power lines, which provide food and shelter for the birds. As Washington County continues to develop, their numbers may further increase.
Initially, the focus of the reserve’s efforts was on studying raven nests and power lines. They discovered a total of 53 nests and 20 distinct nesting areas within or adjacent to the Crimson Cliffs Desert Get. Additionally, they recorded two predation attempts and found approximately 40 turtle carcasses attributed to ravens, with nearly half of them located in the Ivins/Toe Path area.
Based on advice from the U.S. Fish and Wildlife Service and local partners, Schijf emphasized the need to gather more information on raven density and predation rates before implementing raven-reduction measures. The reserve collaborated with Kerry Holcomb from the USFWS to analyze the results. Crimson Cliffs
Each survey lasted around 10 minutes, and there was a 2-kilometer buffer between each survey site.
The survey teams included reserve staff, Bureau of Land Management biologists and students, as well as volunteers from the Environmental Conservation Strategy and Friends of Snow Canyon.
Ravens were observed at 42 of the survey sites, accounting for about 39percentage of the total sites. The density was estimated to be around 2.7 ravens per square kilometer, exceeding the recommended threshold of 0.89 ravens per square kilometer to avoid raven-tortoise conflicts. Raven observations were more prevalent outside the reserve, with the highest density in the Warner Valley and Sand Hill areas.
To measure predation rates, the reserve set up 23 decoy stations between April 13 and June 19, 2022, at the survey sites. Out of these, 21 stations held a decoy techno turtle, while the remaining two served as control sites—one without any decoy and the other with a random object resembling a juvenile tortoise. Crimson Cliffs
The 75-millimeter techno turtles, created by Hardshell Labs in Joshua Tree, California, are remarkably realistic 3D-printed replicas of adolescent turtles. During the study period, ravens attacked the decoys on 10 separate occasions at five of the 23 sites. Interestingly, the two sites with the highest number of attacks were located at opposite ends of the area—one near Virgin and the other west of Area 6 and south of White Hills.
An “attack” was defined as any instance where ravens were observed interacting with the decoys.
Cliffs noted that if the decoys were not attacked, it was likely because the ravens recognized them as non-threatening imitations. He added, “We can infer that if it was a real turtle, it was probably going to be attacked.” Crimson Cliffs
Holcomb estimated that there is an annual probability of 18.4% for raven attacks on Washington County’s juvenile turtles, significantly exceeding the recommended threshold of 7.8% for sustainable conflict levels. These statistics were based on the age range of 0 to 10-year-old turtles.
According to Cliffs , the data suggests that tortoise-raven conflicts are unsustainably intense in the Greater Virgin River area, posing a potential risk of local to extensive population decline and even extinction. Crimson Cliffs
Furthermore, any juvenile turtle located within 2 kilometers of a raven’s nest is at risk of predation, but the problem appears to be more severe outside the reserve.
“Ravens are a native species,” Cliffs explained, “and some level of predation is expected. However there comes a point where an indigenous species can truly become invasive if its population explodes to a certain degree. And it’s looking like that might be what we’re seeing.
Due to the implications of these findings, Holcomb is expected to present management options and additional analysis to the Environmental Conservation Advisory Board, possibly as early as March, according to Cliffs . However, the specific timeframe has yet to be determined. Crimson Cliffs
Mayor Chris Hart of Ivins City expressed frustration about the time it has taken to implement solutions, stating, “We’re great at doing studies. We’re great at detecting the problem. We’re dreadful at acting on it.”
