A study showed that lizards at a US Army facility ate under stress during bridges

The lizards may be small, with only one auditory bone compared to our three, and without ear folds, but their hearing is usually quite good. Most lizards can hear frequencies between 100 and 5,000 Hz (although they are more sensitive between 400 and 1,500 Hz), compared to between 20 and 20,000 Hz in humans. How do lizards react to noise pollution?

Here, scientists studied the effect of noise from low-flying military aircraft on the behavior and well-being of an unfamiliar lizard, the Colorado checkered whiplash (Aspidoscelis neotesselatus). This was done at the US military facility Fort Carson near Colorado Springs, where Apache, Chinook and Black Hawk helicopters fly regularly, and occasionally F-16 transport planes and fighter jets fly over the whiptails’ habitat.

The results are published in Frontiers in amphibians and reptiles. The authors stress that the study could not have been completed without the active cooperation of the US military.

“We show here that noise disturbance has measurable physiological effects on Colorado tails,” said first author Megyn Kebas, Ph.D. student at Utah State University.

Females only

A. neotesselatus is considered a “Vulnerable Species” by the US Army, and a “Species of Special Concern” by Colorado Parks and Wildlife. This species is native to the shrubs and mixed grasslands along the dry creek beds in southeastern Colorado, and consists exclusively of triploid females that reproduce asexually. It is about 30 cm long, including the long, thin tail that gave it its common name.

Numerous A. neotesselatus populations are present on the 550 square kilometers of land belonging to Fort Carson, including 0.05 square kilometers of “Training Area 55” (TA55), the site of this study. Airplanes regularly fly over TA55 at altitudes less than 6 km.

Kebas, Sermersheim, and colleagues conducted a pilot study in 2021. They coordinated with US Army pilots to fly over TA55 at specific times of day between June 23 and 25, 2021, but refrained from flying over this area earlier during the same week. On dates for the bridge, noise readings at ground level ranged from 33.9 to 112.2 decibels—up to the level of an orchestra or electric saw. On the non-bridge dates, it ranged from 30.1 to 55.8 decibels—up to the noise level of a two-ton refrigerator.

Each morning and afternoon, the researchers caught as many unknown individuals as possible, after observing their behavior for three minutes. Each female was captured only once.

The researchers weighed and measured the lizards, drew blood for hormone measurements, and took ultrasounds with a portable device to determine the pregnant females and, if so, the number and size of the developing eggs. Captured females were marked following approved Institutional Animal Care and Use Committee (IACUC) protocols.

Back in the lab, the researchers measured the concentration in preserved blood samples of the stress hormone cortisol, which is secreted by the adrenal glands—under the control of the pituitary gland—within three to 10 minutes after the onset of the disorder. They also measured the concentration of glucose, ketones, and reactive oxygen metabolites (ROMs), such as alkoxy and hydroperoxy free radicals, that are released by mitochondria under oxygen stress.

As expected, serum cortisol concentrations increased sharply immediately after the bridges. However, glucose, ROM, and ketone concentrations were not affected by the upper bridges.

“We found that Fort Carson whiptails exhibit a stress response to plane bridges, after accounting for individual differences in body size and reproductive investment, particularly the number of developing eggs,” said Layne Sermersheim, master’s student at Utah State University. and co-first author of the study.

Noisy whiptails eat more

The results showed that the lizards responded to the noise of the bridge by increasing the level of cortisol and ketones in the blood, indicative of a stress response that rapidly mobilizes more energy resources. Females with developing eggs tend to have a higher increase in cortisol, suggesting that reproductive females may be more susceptible to noise disturbance.

The most obvious effects were on whiptails’ behavior: they spent less time hopping, but more time eating when exposed to noise from bridges.

“Compensatory eating will allow individuals to maintain their energy levels during a stressful event. This is important because metabolism, physical activity, and investment in reproductive and hormonal responses require energy,” said Sirmersheim.