A line of pitfall traps extends out of sight in the field area of a study of how land-management strategies affect ground-dwelling arthropods. (Photo credit: Hayes Goosey)

By Paige Embry

Paige Embry

In dry parts of the west dominated by sagebrush and grasses, Greater sage grouse (Centrocercus urophasianus) males strut and jockey for mates. Between 2012 and 2015, the grouse strutted around that frat party staple, plastic Solo cups, which scientists had buried in the ground as pitfall traps. The scientists wanted to learn more about the terrestrial arthropods that provide needed protein for sage grouse and other birds, particularly the young chicks. The paper on this research was recently published in Environmental Entomology.

The grouse’s range, which extends over parts of 11 states, has shrunk by nearly half. Chunks of the rest have fragmented and degraded, putting the grouse and some of the 350 species of animals that live in this sage-steppe habitat in peril.

Hayes Goosey of Montana State University led a study focused on how different land-management strategies affect insects available for sage grouse chicks’ consumption on the ground. (Photo credit: Hayes Goosey)

Much of that same land is used by ranchers for grazing, and in 2015 the Obama administration adopted the Sage Grouse Initiative (SGI) as an alternative to placing the sage grouse on the Endangered Species list. The SGI brings together all the stakeholders—the federal government, states, ranchers—in an effort to find ways to support both the grouse and the grazing. Such research tends to focus on the birds themselves or plants—how tall should they be to provide cover, for example—but this study takes a different approach.

Hayes Goosey, a research assistant professor at Montana State University, is the lead author on the Environmental Entomology paper and says that even for people heavily involved in sage grouse conservation, the study “shed a whole new light on how to look at insects in terms of conservation of grouse and rangelands as a whole.”

Sage grouse chicks can’t fly, so they scurry around, gulping down whatever arthropods they can get their beaks on. For the youngest chicks, that is mostly ground-dwelling insects in only a few orders: Orthoptera, Coleoptera, Hymenoptera, and Lepidoptera. The researchers set out to find how different kinds of land use management affect this food supply.

Between 2012 and 2015 the researchers sampled plots in three different management situations: grazed, resting, and idle. The first two were plots being managed as part of a rest-rotation scheme meant to aid various conservation goals by mimicking the movement of wild herbivores. Ranchers create a series of pastures and move the animals through them so that each area gets a rest period of around 15 months. The researchers collected arthropods from pastures while they were actively being grazed as well as “resting” plots. They also collected specimens from a nearby wildlife refuge that hadn’t been grazed in more than 10 years, the “idle” plot.

If you’re studying arthropods, one of the key questions is how to collect them to get the needed information. Sweep nets? Vacuuming? Traps? The researchers chose pitfall traps—those Solo cups buried in the ground. These traps collect whatever happens to walk into them and so provide only a small window into the overall insect population. Goosey says that since they were interested in what a flightless sage grouse chick could potentially eat, “The pitfall traps were by far the best choice.”

One of the biggest surprises in this study for Hayes Goosey was coming across a Lycosid spider in a pitfall trap. (Photo credit: Hayes Goosey)

Over the four years of the study, the researchers captured 37,000 arthropods from 54 families. They collected twice as many arthropods in the long-ungrazed wildlife refuge than on the the managed land—but that didn’t translate into more sage grouse food. The wildlife refuge had three times as many detritivores and twice as many predators as the managed lands, likely due to higher levels of plant debris on the ground. The managed land, conversely, had twice as many arthropods that fell into the “food” category.

Goosey isn’t surprised by this finding. He says it’s important to remember the historical context. This land was routinely grazed before livestock arrived—only by bison and other native grazers—so it makes sense that sage grouse tend to eat the kinds of arthropods that thrive in a sage-steppe habitat that is moderately grazed. Goosey says, “Grazing is a tool … grazing itself is not inherently bad. Through that evolutionary context, it is a part of these native landscapes.”

Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.