New research shows drought conditions drive deer populations to croplands, urban environments

LOGAN — Utah’s drought conditions are far from a secret, and the impacts are widespread.

Currently, most of the state is in a moderate or severe drought, according to data from the U.S. Drought Monitor. While droughts can have far-reaching impacts on water infrastructure, they can also affect wildlife habitat conditions.

Utah’s extreme drought from 2020 through early 2023, which ended with a record statewide snowpack, was a double-whammy for deer populations, Dax Mangus, big game coordinator for the Utah Division of Wildlife Resources, told KSL in July.

Drought impacts the species by gradually reducing food and habitat options in wild spaces, ultimately leading to deaths from malnutrition. The record snowpack that saved the state from drought also produced large-scale die-offs, prompting some emergency feeding measures at the time.

However, new research out of Utah State University tracked movements of mule deer during drought and found that when water content in plants dropped to a specific low, it triggered the animals to abandon their natural habitat, often in favor of irrigated croplands and urban landscaping.

The research team, led by extension specialist David Stoner, used data from the ECOSTRESS sensor, a new, experimental instrument carried on the International Space Station that measures evapotranspiration — how much water moves through plants in response to heat and sun. The satellite imagery allowed them to track how dry natural habitats get compared to nearby irrigated lands like alfalfa fields and home gardens.

Tracking deer across Utah, Sevier and San Juan counties, the team compared ungulate movements during an average water year like 2019 to extreme drought conditions the state faced in 2021.

Researchers determined drought conditions drove mule deer to change habitat when the water content of plants they eat reached the low threshold.

During a typical year, Stoner said, mule deer used shrub habitat 57% of the time and spent only 6% in croplands. During acute drought, use of natural habitat dropped to 44%, and time in irrigated croplands doubled.

“The quality of natural habitats can vary tremendously,” Stoner said in a statement. “But irrigated landscapes offer food for wildlife even during the hottest, driest parts of the year. When we produce a veritable garden of Eden in a drought, it can be hard for deer to resist.”

Stoner added that deer rely on plants for both food and water during the summer. When those plants don’t have the necessary moisture content, deer are forced to take additional risks to seek alternatives.

Unsurprisingly, the journey from the wildlands to more urban environments pose a big risk for deer populations, as they run the risk of being hit by cars, caught in fences, chased by dogs and harassed by landowners.

This migration can also impact farmers and gardeners, with the ensuing crop damage being a costly issue for agricultural producers in the state.

Stoner hopes the ECOSTRESS sensor can serve as a tool for land and wildlife managers alike to better predict when deer might be on the hunt for more moisture-rich food sources and employ safety measures like temporary fencing to direct wildlife away from high-risk croplands.

“The big goal is to minimize conflict and keep deer and people safe,” Stoner said in a statement.

The full study can be found here.