Rodents share the blame for the decline of three bird species found in sagebrush habitat near oil and gas wells in Wyoming, a University of Wyoming researcher has found.
Anna Chalfoun, an associate professor in zoology and physiology at the University of Wyoming, started studying the Brewer’s sparrow, sagebrush sparrow and sage thrasher in 2008. Chalfoun wanted to know what happened when energy development and infrastructure encroached on landscapes where songbirds nest in the cover of sagebrush.
About 50 percent of North America’s sagebrush steppe has disappeared with development, and few of the remaining lands are managed in a pristine state. Sage grouse garner most of the attention when looking at how change in that habitat has impacted species in Wyoming, Chalfoun said.
The three bird species she studied, which also live in the sagebrush steppe, are declining, and not just because of habitat loss. Their nests in the sagebrush are seeing increased predation.
Chalfoun began her research by looking at how the bird’s nesting success varied depending on proximity and intensity of development on the landscape.
She found nest survival decreased for all three birds as development increased. She also learned nests closest to reclamation areas had the highest failure rate, even when compared to nests near roads or well pads. But she didn’t know why.
“We knew there was something going on with reclaimed areas,” she said.
Chalfoun then set up 24-hour infrared cameras on the nests of three species of songbirds in the Jonah Field and the Pinedale Anticline. The cameras produced evidence that a suite of species attack the nests, but 90 percent of the predators were rodents.
Brewer’s sparrow nests were attacked mostly by deer mice, which are the same size or smaller than the nestlings they were killing.
“It was like ‘Whoa,’” Chalfoun said. “They were just so aggressive.”
Chalfoun hadn’t expected to see so many mice pillaging nests. She wanted to know why there were so many rodents in areas close to energy development.
She hypothesized first that predators, specifically hawks and eagles, were less abundant in energy fields, allowing mice populations to grow and thrive. But raptor surveys showed the birds weren’t avoiding the areas with more mice.
Next Chalfoun wondered if rodents find food subsidies in reclaimed areas. Russian thistle and smooth brome are the predominant plants found in some reclamation areas, which changes the structure and composition of the adjacent habitat, Chalfoun said.
That’s a harder question to answer, or even study, because there are so many variables. Chalfoun is getting help from Lindsey Sanders, a master’s student at the University of Wyoming. This spring, Sanders plans to complete a dietary analysis of the mice found in reclaimed areas, compared to other landscapes. The dietary research should tell them if food is playing a role, and maybe even specifically what food, in the abundant rodent population living in reclaimed landscapes, Chalfoun said.
But they are also looking at other reasons potentially responsible for so many mice in reclaimed areas. The rodents could be finding shelter and protection for nests in buildings and sheds used for energy development, Chalfoun said.
Sagebrush songbirds come from wintering grounds in the Southwest and Mexico to breed in the sagebrush landscape. That hasn’t changed. Development apparently doesn’t signal danger for nesting, Chalfoun said.
“As long as they find sage, they nest,” she said.
These patches of sage near development are like “ecological traps,” Chalfoun said.
Songbirds already face challenges to survival, Chalfoun said. Predators like raptors attack nests, but inadvertently many other species, from ants, to deer, to cows, degrade nesting areas. Chalfoun wants to provide specific information that can be used for songbird conservation and management.
The information Chalfoun has documented can help with management. If mice are thriving because they are finding safety in buildings at energy sites, setting traps in the buildings might decrease the population, she said. If reclamation is offering rodents food subsidies, land managers can change what species are planted near sagebrush habitat.
This article has been corrected to say Russian thistle is often found in some reclamation areas, not specifically used in reclamation— Ed.