Researchers track cows to determine riparian area impact

A cow and calf drink from Catherine Creek in Union County. Using GPS tracking collars over five grazing seasons on federal land, researchers determined cows spend 1 to 2.5 percent of their time in streams.

A five-year study of cattle grazing on federal rangeland showed they spend only 1 percent to 2.5 percent of their time in streams or in riparian buffer areas, a finding that may prove important as debate continues over the impact of cattle on public land.

Researchers at Oregon State University outfitted cows from three ranches with homemade GPS tracking collars and mapped their positions during spring to fall grazing seasons over five years. The collars reported the cows’ positions about every five minutes and compiled more than 3.7 million data points over the course of the study. The technology was able to pinpoint when the collared cows were within 30 meters of streams.

The study took place on federal grazing allotments in the Wallowa-Whitman and Umatilla national forests. The findings are potentially significant because critics of public land grazing practices have long contended cattle trample and erode streambanks and pollute water.

But John Williams, an OSU Extension rangeland expert in Wallowa County, said cows enter riparian areas for two reasons: “One is to drink, the other is to cross,” he said.

The cows typically did not rest or graze near streams. Instead, they spent most of their time grazing on higher ground or resting in dry areas away from streams, according to Williams.

Not surprisingly, the location of good forage was the primary factor in their movement. Water sources, fences, and previous logging or fires also influenced cattle movement, as did topography and the herd’s point of entry at the beginning of the season. Cows used 10 to 25 percent of the stream area in each grazing allotment.

Williams said the findings could be important to livestock management. The cattle impact on riparian areas “isn’t for very long, and it isn’t for all of the stream,” he said. “What might we look at in management options that let us be more efficient?”

Cows were more likely to enter stream areas during the heat of summer, but in the cool spring showed little interest in riparian areas, Williams said. That suggests adjusting management practices across the seasons may be appropriate.

“If talking about riparian pasture grazing in April, maybe it isn’t a big issue,” he said. “But in August, maybe you take a look at it in a different light.”

Williams said he’s shared the study findings with the U.S. Forest Service, which manages grazing allotments in the national forests.

“I believe it’s real straight forward in terms of, here’s where cows go,” he said.

The study had some quirks. Researchers selected cows at random from among the 300 to 400 in each of the three herds, and kept some of them collared for several years. About a third of the collared cows were new each year as older participants were sold or disappeared, or collars wore out.

Williams said funding for the research was tight, and the team chose to make their own GPS collars to save money. They bought plastic boxes to hold the electronics, made leather collars to fit around the cows, bought motherboards and “soldered, taped and glued” the devices for about $450 apiece in material. Williams said he was told pre-assembled GPS units would have cost $2,000 to $3,000 each.

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