Predator poop tells researchers about diet, but it’s not all about carnivores in the scat world. Ungulates like elk and mule deer leave data-rich pellets for scientists to collect across the landscape. It is possible to determine food items from ungulate scat, but when I started working in the University of Missouri’s Wildlife Physiology Lab, we were using scat samples for a different reason: to determine stress levels.
To understand how we’re getting to those stress levels using a couple of scat pellets, let’s take a step back. Ungulates (and lots of other animals, including humans) have something called the hypothalamus-pituitary-adrenal axis (HPA axis) that, among other things, responds to stressors. One HPA axis reaction to stress is an increase in glucocorticoid production. Glucocorticoids, also known as stress hormones, signal the body to produce glucose faster than normal and distribute it primarily to the heart and brain, resulting in a fight-or-flight response.
Researchers can find these stress hormones in scats, and a higher concentration means a more stressed animal. It isn’t a big deal for occasional spikes in stress hormones. For example, we might see an increase in glucocorticoids in an elk as it notices and runs from a predator or in a human before a big speech. But, a long-term increase in stress hormone production can have negative results, including immune system suppression, issues with reproduction, and ulcers, all of which reduce the overall fitness of an individual. It is important to understand if and why ungulates are chronically stressed so we can better manage the herd.
After we received scat samples in the lab, we mushed together the pellets in each sample and collected a small subsample in a vial. We completely dried the subsample and I then had the glorious job of turning that clump of dried poop into what I referred to as “poop dust” using a small mesh sieve. We mixed the poop dust with an ethanol solution that pulled those stress hormones from the samples. Then, we used a special kit to determine the glucocorticoid concentrations in each sample.
We can use those concentrations to get an idea of how stressed the herd is as a whole. Take the Missouri elk herd as an example. Elk were recently reintroduced into the state from Kentucky (you can read more about Missouri’s elk here and here). We can imagine that the move was a high-stress time for the elk. But after spending several years in Missouri, we would expect their stress levels to be lower overall. They might still experience seasonal changes in stress, however. For example, the increase in disturbance caused by humans during white-tailed deer hunting season might trigger an increased stress level that time of year.
Researchers can use these same methods to test various potential stressors in other ungulate herds, too. So, the next time you come across a deer scat, skip the “Ew!” and consider how cool that pile of pellets really is!