Looks like humans aren’t the only ones who stress-eat.

A new study published in Frontiers in Amphibian and Reptile Science by Utah State University found that lizards at a Colorado Army post change their eating habits when bombarded by noise pollution such as helicopters and planes.

“Here 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,” said first author Megen Kepas, a doctoral student at Utah State University.

The research was conducted at Fort Carson near Colorado Springs, Colorado, where Apache, Chinook, and Blackhawk helicopters regularly fly along with the occasionally transport aircraft and F-16 fighter jets.

The whiptails’ behavior showed when exposed to flyover noise, they spent less time moving around and more time eating.

The US Army classifies the whiptail as a “species at risk,” and Colorado Parks and Wildlife classifies it as a “species of special concern.” The species only consists of triploid females that reproduce asexually and is native to shrubland and mixed grassland along dry creek beds in southeast Colorado. The 30-centimeter tail gave them their common name.

Their hearing is excellent, which is part of the problem. Most lizards can hear frequencies between 100 and 5,000 hertz (though they are most sensitive between 400 and 1,500 hertz), whereas humans can hear frequencies between 20 and 20,000 hertz.

The research was conducted in ‘Training Area 55’ (TA55). Aircraft regularly fly over TA55 at altitudes below 6km.

An experiment was performed in 2021 by Kepas, Sermersheim, and fellow researchers. In coordination with U.S. Army pilots, they flew over TA55 on the 23rd, 24th and 25th of June, at predetermined times of the day. On flyover dates, the noise readings at ground level ranged from 33.9 to 112.2 dB – 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.

Stress eating

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

To determine which females were pregnant and the number and size of their developing eggs, the researchers measured and weighed the lizards, drew blood for hormone measurements and performed ultrasounds with a portable device. Protocols approved by an IACUC were used to mark the captured females.

Back in the laboratory, the 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 disturbance onset. Under oxygen stress, they also quantified the release of glucose, ketones, and reactive oxygen metabolites (ROMs) like alkoxy and hydroperoxy free radicals.

As expected, the blood concentrations of cortisol sharply increased immediately after flyovers. However, flyovers did not affect glucose, ROMs, or ketone levels.

The findings demonstrate that the lizards’ increased blood cortisol and ketones levels in response to flyover noise are signs of a stress response that quickly releases more energy reserves. Cortisol levels increased more frequently in females with more developing eggs, suggesting that these females may be more sensitive to noise disturbance.

“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,” said Layne Sermersheim, a master’s student at Utah State University and the study’s co-first author.

Humans also fall prey to stress eating (or emotional eating). While this is commonly a coping mechanism term commonly refers to eating as a means of coping with negative emotions, it is sometimes linked with positive emotions, such as overeating when celebrating an event or enhancing an already good mood. The link between pollution and stress eating is imperfectly understood.