A new study that used satellite imagery to monitor the movements of cows and tule elk in the Point Reyes National Seashore could help the park manage grazing conflicts and monitor the spread of Johne’s disease.
Researchers from the University of California, Santa Barbara, collected satellite images along with GPS collar data and in-person observations from 2010 to 2017 to track the animals. They found that cattle were the primary drivers of the elks’ choice of habitat, and that the elk avoided cattle and tended to stick to their own grazing areas on and off ranchland.
Still, the study’s lead author, Lacey Hughey, a former U.C. Santa Barbara researcher who now works for the Smithsonian Conservation Biology Institute, said that won’t necessarily always be true. “That can always change as you get major climate change, or more cattle, or a lot more elk,” she said.
Ms. Hughey worked for the seashore for five years, first as a wildlife technician and then as a biological technician on a trail crew. As a Ph.D. student, she first used the satellite study method on herds of wildebeest in East Africa.
David Press, the seashore’s wildlife ecologist, called the study “a robust analysis of what we observe in the field on a regular basis,” like the fact that elk instinctually congregate on ridges. The study was helpful, he said, in identifying the characteristics of the elks’ preferred grazing areas, so the park can try to guide the animals toward similar areas outside of ranchland. He said the findings provide a hope that, as long as the elk population is managed, “there is a way to make this all work out there.”
Ranchers in the areas where the Limantour and Drakes Beach herds were introduced have reported grazing conflicts with their animals, as elk and cows tend to graze on the same plants. Although the study found that elk avoided cattle, it did not monitor the forage itself. Mr. Press said it’s possible that as drought conditions continue, elk could spend more and more time on pastures where they can find hay, or better grass.
“If we were to have conducted this study at a time when the elk were really getting into the hay a lot more, there might be some different results to discuss in this paper,” Mr. Press said. “The potential for conflict is still present, despite the findings of this study,” he added.
The two free-ranging elk herds in the park, which can enter pastures by jumping fences or walking through damaged portions of fence, are stable or growing. The Limantour herd only lost nine animals last year—a drought year that left the park’s fenced Tomales Point herd with poor forage—and the Drakes Beach herd grew by one.
Zoonotic disease can also affect interactions between elk and cattle. Johne’s disease, a bacterial interaction that attacks the intestines of both species, was found in the park’s elk in 2016. Ms. Hughey is optimistic about the potential for using satellite images to monitor the spread of diseases like Johne’s, but she said no one has yet studied transmission with this data.
The park service’s plan to cull members of the Drakes Beach herd and allow longer ranching leases was accepted by the California Coastal Commission last week.