Tracking Grazing Impacts on Sage Grouse Food
Biologists Learn That Livestock Increase Bug Numbers
They crawl or fly, buzzing, seemingly extraterrestrial, sometimes around a head and lights. And many animals eat them, making insects an important part of the diet of everything from snakes to greater sage grouse.
Every insect has a story going.
— Henry Trujillo, Entomology student
These characteristics and more make the creepy crawly interesting to entomologists Grace Overlie and her lab assistant Henry Trujillo.
The duo has been sorting insects — as well as arthropods such as scorpions and spiders — into their prospective families as they count, measure and identifying bugs captured in traps and nets, and bagged, as part of a years-long sage grouse study being conducted by University of Idaho.
Researchers wanted to know if spring cattle grazing reduces the number of insects available to young sage grouse, a food chicks rely upon in the first several weeks of their life.
The study was part of a bigger project that investigated factors that may be linked to sage grouse population declines throughout the Rocky Mountain West. As part of the study, scientists investigated whether cattle grazing reduced the abundance of insects. Arthropods are a key food source for greater sage grouse chicks. Research shows that more than 90% of the diet of one- to four-week-old chicks is composed of arthropods.
Overlie, who is compiling data as part of her U of I master’s research project in entomology learned that more insects and arthropods are found in sage lands grazed by cattle.
“Spring grazing resulted in more abundant insects as well as more groups of insects,” Overlie said. “Insects found under the spring grazing treatment generally have a larger biomass, which could provide more food for sage-grouse.”
Arthropods collected in pastures grazed by cattle weigh more, and there are more of them, she said. The findings will become part of the sage grouse research literature going forward, but the work continues as Overlie and Trujillo work in a lab in the basement of the College of Natural Resources.
“We have identified more than 270,000 specimens,” Overlie, who grew up in Lowman, Idaho, said. “We’re at sample 3,212 right now.”
Trujillo, U of I’s Entomology Club president, became interested in insects as member of the Meridian FFA chapter.
“Every insect has a story going,” he said. “There’s always some surprise the further you look at it.”
In Overlie’s lab, Trujillo uses a stereo microscope to get an up-close-and-personal look — right down to the number of spines on an insect’s legs, which distinguish it from another species — at the bugs that have been collected.
“The work I’m doing is going toward conservation. It’s going to make an impact,” he said. “Having that experience in undergraduate level is very valuable.”
Master’s student Grace Overlie made a key to help assistants identify insects caught in pitfall traps.