These uncommon reptiles, called Colorado checkered whiptails, are engaging in compensatory feeding behaviors when low-flying Apache, Chinook and Blackhawk helicopters — and sometimes F-16 fighter jets — swoop over their habitat, according to the study, published on Wednesday in Frontiers in Amphibian and Reptile Science.
Lizards tend to have excellent hearing and are sensitive to much lower frequencies than humans are, the study authors explained.
Colorado checkered whiptails are members of a species considered “at risk” by the Army and “of special concern” by Colorado Parks and Wildlife, the researchers noted. The species, which lives in shrubs along dry creek beds, consists exclusively of females who reproduce asexually.
As several populations of Colorado checkered whiptails inhabit the 212-square-mile tract of land that belongs to Fort Carson, the scientists coordinated with the U.S. Army to explore how these animals react to noise.
Army pilots flew over a 0.02-square-mile portion of the base known as “Training Area 55” at pre-selected times for three days in June 2021, after abstaining from doing so earlier in the week, according to the study.
During the flyover days, noise readings at ground level ranged from 33.9 to 112.2 decibels — what the authors described as “the sound level of an orchestra or a power saw.”
On non-flyover dates, noise levels hovered between 30.1 and 55.8 decibels, or about the range of a humming refrigerator, they explained.
The researchers observed the behavior of 82 lizards and then brought them in for weight measurements and blood tests, as well as ultrasounds to determine whether they were pregnant and the quantity and size of developing eggs, according to the study.
By evaluating the blood samples, the authors were able to ascertain levels of the stress hormone cortisol, which is typically released between three and 10 minutes after a disturbance.
Blood concentrations of cortisol rose sharply immediately after the flyovers, in what the authors described as “a stress response that rapidly mobilizes more energy resources.”
Lizards with developing eggs exhibited bigger surges in cortisol, indicating that reproductive females could be more vulnerable to noise, according to the study.
In addition to exhibiting such shifts in cortisol levels, the lizards also spent less time moving and more time eating following exposure to flyovers, the authors found.
“Compensatory eating would allow individuals to maintain their energy levels during a stressful event,” co-first author Layne Sermersheim, a master’s student at Utah State University, said in a statement.
“This is important because metabolism, physical activity, investment into reproduction and hormonal responses require energy,” Sermersheim added.
While the noise disturbance does have physiological impacts on the animals, they are also “somewhat resilient and may compensate for this to some degree,” according to first author and doctoral candidate Megen Kepas.
Nonetheless, Kepas and Sermersheim advised the Army to take certain “cautious management” steps that could help ensure the “local abundance” of the lizards at Fort Carson.
“We suggest that military aircraft operators attempt to avoid dense populations of [checkered whiptails] during the reproductive season or fly at altitudes that lead to decibel reads that fall below 50 [decibels] at ground level,” the authors added.