As bighorn sheep herds continue to face disease and die-offs across the West, those that live in a specific area in Idaho are thriving. With more than 1,000 bighorn sheep populating the canyons of the John Day River and its tributaries, researchers at the University of Idaho are trying to determine why they seem to flourish there while other populations elsewhere struggle, according to a news release.

Graduate students Emily Lowrimore and Alexis Means are working with Ryan Long, associate professor of wildlife sciences, to collect and analyze data on the herd in an effort to understand why it remains healthy and stable.

“We’re trying to understand the different contributing factors that make this population of bighorns so healthy, and to learn if we can apply those qualities to other populations that may be struggling with disease or just population numbers in general,” said Lowrimore.

Specifically, Lowrimore and Means are studying how food sources may influence behavior and survival without focusing on the influx of pneumonia, which is a major factor in healthy wild sheep herds. To do this, they’re looking at whether the type of forage is “keeping the herd fit and resilient” as well as “behavioral factors such as group dynamics.” 

For instance, Lowrimore thinks bighorn sheep that congregate in larger groups “may have an advantage against predation,” which includes larger nursery groups compared to the lower survival rates of smaller nursery groups – that is groups comprised mainly of ewes and lambs. John Day bighorn sheep nursery groups include about 80 bighorn sheep while the healthy herds along the Snake River only contain about 20 members.

“In larger nursery groups the more eyes there may be more eyes looking out for danger,” said Lowrimore. “Individual sheep can feed more freely as other sheep stand guard which allows sheep to alternate between keeping watch and eating.”

Food also plays a factor – both in availability and nutritional value. Cheat grass is a big staple of the John Day’s herd’s diet.

“Grasses, grasses and more grasses,” said Means, who is tracking what foods the John Day herd prefers during different seasons. “Much of the area is overrun with invasive plants such as cheat grass. When it’s small and green this grass can provide a really good food source before it dries up.”

While this study focuses solely on the John Day herd, the hope is that the research and analysis will be able to be applied to other bighorn sheep herds across the West.

“It’s useful to understand what are the factors that limit populations like this in the absence of disease,” said Long.