Lizards living near loud military base comfort eat to cope with stress: study

By Stephen Beech via SWNS

Lizards living near an American military base comfort eat to cope with stress caused by noisy aircraft, according to new research.

Colorado checkered lizards invest in maintaining energy levels to compensate for sound stress, say scientists.

They explained that while lizards may be small, with only a single hearing bonelet compared to our three, and without earflaps, their hearing is typically good.

Most can hear frequencies between 100 and 5,000 Hz, compared to between 20 and 20,000 Hz in humans.

Scientists studied the impact of noise from low-flying military aircraft on the health and behavior of Colorado checkered whiptails at the Fort Carson US military Installation near Colorado Springs, where Apache, Chinook, and Blackhawk helicopters regularly fly over.

Large transport aircraft and F-16 fighter jets also sometimes fly over the whiptails’ habitat.

The research team said their study, published in the journal Frontiers in Amphibian and Reptile Science, couldn’t have been conducted without the active cooperation of the US Army.

First author Megen Kepas, a doctoral student at Utah State University, said: “We show that noise disturbance does have measurable physiological impacts on Colorado checkered whiptails.

"We also show that they are somewhat resilient and may compensate for this to some degree by altering their feeding and movement behaviors."

The species is considered 'at risk’ by the US Army, and a ‘species of special concern’ by Colorado Parks and Wildlife.

It is native to shrubland and mixed grassland along dry creek beds in southeastern Colorado and consists exclusively of triploid females that reproduce asexually.

They are about 30 cm (12 inches) long, including the long, thin tail that gave them their common name.

Several populations of checkered whiptails live on the 550 square kilometers (212 square miles) of land belonging to Fort Carson, including the 0.05 square km of ‘Training Area 55’ (TA55), the site of the study.

Aircraft regularly fly over TA55 at low altitudes.

The research team coordinated with US Army pilots to fly over TA55 at pre-chosen times of the day between 23 and 25 June 2021, but to abstain from flying over the area earlier during the same week.

On flyover dates, the noise readings at ground level ranged from 33.9 to 112.2 decibels – up to the sound level of an orchestra or a power saw. On non-flyover dates, they ranged from 30.1 to 55.8 dB – up to the noise level of a humming fridge.

Each morning and early afternoon, the researchers caught as many unmarked lizards as possible, after observing their behavior for three minutes. Every female was caught only once.

The researchers weighed and measured the lizards, drew blood for hormone measurements, and took ultrasounds with a portable device to determine which females were pregnant, and if so, the number and size of their developing eggs. Caught females were marked following approved protocols.

In the lab, researchers measured the concentration in preserved blood samples of the stress hormone cortisol, which is typically released by the adrenal glands – under control by the pituitary – within three to 10 minutes after the onset of disturbance.

They further measured the concentration of glucose, ketones, and reactive oxygen metabolites (ROMs), such as alkoxy and hydroperoxy free radicals, released by the mitochondria under oxygen stress.

As expected, the blood concentrations of cortisol sharply increased immediately after flyovers.

However, glucose, ROMs, and ketone concentrations weren’t affected by flyovers.

Study co-first author Layne Sermersheim said: “We found that whiptails at the Fort Carson show a stress response to aircraft flyovers, after we accounted for individual differences in body size and reproductive investment, in particular the number of developing eggs."

The results show that the lizards reacted to flyover noise by increasing their level of blood cortisol and ketones, indicative of a stress response that rapidly mobilizes more energy resources.

Females with more developing eggs tended to have a higher increase in cortisol - indicating that reproductive females may be more susceptible to noise disturbance, according to the research team.

The clearest effects were on the whiptails’ behavior: they spent less time moving about, but more time eating when exposed to noise from flyovers.

Ms Sermersheim, a master’s student at Utah State University, added: “Compensatory eating would allow individuals to maintain their energy levels during a stressful event.

"This is important because metabolism, physical activity, investment into reproduction, and hormonal responses require energy."