JACKSON — Though mule deer on winter range have sagebrush shoots poking through the snow to munch on, the nutrients they offer are essentially unavailable to them around Wyoming gas pads.
That’s one conclusion of a just-published University of Wyoming study, research that helps explain why the deer population in the Pinedale Anticline dropped by 36% over a 15-year period during which the field was being drilled out.
UW research scientist Samantha Dwinnell is the lead author of the paper “Where to forage when afraid: Does perceived risk impair use of the foodscape?” She said that the role of food was a “missing link” in past research that investigated how energy development affects deer.
“Are they no longer using the landscape the way that they would be, without that disturbance present on it?” she asked rhetorically in an interview with Jackson Hole Daily. “And that’s what we found with this research. ... We’re seeing they’re not really taking that risk and using that food that’s available to them there.
“Instead,” Dwinnell said, “they’re just not using it.”
Because deer winter ranges are finite areas dependent on vegetation, topography, snow cover and other variables, they have definable carrying capacities for the number of animals that can survive on them till spring. When gas pads, roads, pipelines and other industrial infrastructure share those landscapes, Dwinnell found, the ranges functionally shrink.
She put numbers to it. Overall she found that there was a 4.6-fold “indirect habitat loss” multiplier that extends beyond the actual footprint of disturbed areas, but results varied significantly one gas field to the next.
The most damaging in terms of mule deer’s use of their range was the Anticline, a nearly 200,000-acre expanse of Bureau of Land Management property south of Pinedale where about 20% of sagebrush shoots were being left on the stem.
At the opposite end of the spectrum, only 4.3% of mule deer forage was eschewed on Wyoming Range winter habitat that overlaps the Labarge Oil and Gas Field. Wyoming Range deer that winter further south were functionally losing around 11% of their habitat.
Although variable, impacts were documented across the board.
“Across three winter ranges and different development scenarios,” the researchers wrote, “mule deer avoided areas close to disturbance, tended to move away from disturbance, and increased vigilant behavior near disturbance.”
While mule deer were more on alert — and thus less likely to be eating — near disturbed areas, the nutritional effects of their vigilance are likely negligible relative to habitat that’s going unused, Dwinnell said.
More research, she said, could help explain why deer were more displaced in some places than others.
The dense and more bustling nature of the Anticline, which wasn’t developed until the 1990s and has significant “infill” drilling on already occupied pads, could partly explain the difference.
But another factor, Dwinnell said, appears to be topography: The least-affected habitat, in the northern Wyoming Range, is rugged and hillier, while the Anticline is the flattest landscape and also where the most mule deer forage goes unused.
“I wish we knew why,” Dwinnell said. “It’s probably a combination of a lot of things. It’s hard, because these animals, they use senses that we humans aren’t quite as in tune with.”
Collaborators on the research include Hall Sawyer, Jill Randall, Jeff Beck, Jennifer Forbey, Gary Fralick and Kevin Monteith. The Ecological Application paper that just published was a chapter from Dwinnell’s graduate thesis. It took two years to navigate the journal’s submittal and peer-review processes.
The findings, Dwinnell said, corroborate the effectiveness of some steps the oil and gas industry is already taking to minimize habitat degradation, like directional drilling.
“Development is occurring on these landscapes — it’s inevitable, a needed resource and a huge part of the state’s economy,” she said. “Really what this research is providing is a more realistic understanding of what we can expect when this development happens.”