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New study finds differences in bighorn sheep migrations

Bighorn sheep

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Does every bighorn sheep herd follow the same migration pattern? Not necessarily. A new Montana State University (MSU) study has discovered “diverse patterns of migration among different sheep populations,” ScienceDaily reports. The paper, which was published in the journal Ecology and Evolution in July, used data collected by the Greater Yellowstone Mountain Ungulate Project (GYMUP) and the Montana Bighorn Initiative (MBI) and included 18 different populations of bighorn sheep.

“This paper is the first to quantify migratory diversity in ungulates and start to ask questions about how our understanding of migratory diversity can influence sheep populations and their restoration,” said lead author Blake Lowrey. Lowrey is now a postdoctoral researcher in MSU's Department of Ecology in the College of Letters and Science. Lowrey completed his Ph.D. in November.

MSU ecology professor and co-author Robert Garrott, who leads GYMUP and MBI, says that this is the “largest coordinated research effort on bighorn sheep” ever started. According to ScienceDaily, between 2008 and 2017, 209 bighorn sheep ewes from the Rocky Mountains in Montana were outfitted with GPS collars to monitor their movements. Blood samples, nasal and tonsil swabs were also taken during that time to provide possible “insight for disease and pathogen work.” 

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"Putting that all together provides a really rich data set to address a number of important topics related to bighorn sheep management," Garrott said.

Using data collected from GPS collars, Lowrey was able to piece together migration patterns, identifying summer and winter ranges and measuring the elevation and geographic distances between them. He discovered that native bighorn sheep herds went on longer, more frequent migrations than those in restored or recovered populations that had short migrations or no migrations at all. 

“Migratory patterns in ungulates are thought to be learned,” Lowrey said. “If you remove animals from the landscape, you lose the herd memory needed to maintain a diversity of migratory patterns.”

Lowrey’s research shows why differences in migratory patterns are important to wildlife.

“Practically, it’s not putting all of your eggs in one basket,’ said Lowrey. “Without migratory diversity, an extreme winter event or other negative factors that could negatively impact all of the population. Migratory diversity may buffer bighorn sheep and not expose all of the population to the same harmful conditions.”

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