In 2003, experiments showed wolves refuse to cross a line of fluttering flags, so ranchers now string 'fladry' around calving pens as a cheap, non-lethal way to keep the predators off herds

If you've driven past a cattle pasture in Montana, Idaho, or Wyoming and noticed a rope along the fence line with little flags flapping in the wind, you've seen fladry in action. According to the 2023 study published in Conservation Biology by researchers from the University of Calgary, the University of Rome, and the U.S. Fish and Wildlife Service's National Wildlife Research Center, that strip of fabric can genuinely make a wolf think twice before crossing.

Where the idea actually came from
Fladry is nothing new. Flag lines have been used for centuries by hunters in Eastern Europe and Russia to funnel wolves into traps. In 2003, a research team decided to turn that old trick on its head: what if, instead of using flags to herd wolves towards danger, the same visual cue could be used to keep wolves away from livestock?

Why this matters for American ranchers today
Since reintroduction efforts began in Yellowstone National Park and central Idaho in the mid-1990s, wolf populations across the northern Rockies have been rebuilding, and that recovery has been a conservation success. But it also means more overlap between wolves and working cattle and sheep operations throughout Idaho, Montana, and Wyoming. Lethal control is limited in many areas by federal protections, and many ranchers would prefer not to kill a wolf if there’s an alternative to protecting a herd.


What the 2003 experiments actually found
The research team tested fladry on nine captive wolves in large enclosures in Italy and on wild wolves in Alberta and Idaho. The flags themselves were simple: strips of plastic sewn onto a nylon rope, strung approximately knee-high off the ground on posts some 30 meters apart.

The 2003 study, titled ‘Wolf Depredation Trends and the Use of Fladry Barriers to Protect Livestock in Western North America,’ found that the barrier kept captive wolves away from a food source for as long as 28 hours before hunger won. Out in the wild, the results were even more striking, at least for a while. During 60-day trials around two 25-hectare cattle pastures in Alberta, wolves approached the flag line 23 separate times, sniffing, pacing, clearly wary, but never crossed it, and no cattle inside those pastures were touched.

Idaho had a slightly different story. On a much larger 400-hectare ranch, four radio-collared wolves eventually crossed the fladry line and killed cattle, but only after 61 days of exposure to the barrier. The flags did not work indefinitely; they provided about two months of protection before the wolves figured out how to get around them.

The flags buy time, they don't solve the problem
The study found that wolves near the flag line spent significantly more time sniffing the air and pacing close to it than they did under normal conditions, suggesting wariness rather than indifference. The most likely explanation is that wolves are naturally suspicious of unfamiliar objects, and it is the wariness, not any physical barrier, that prevents them, at least until hunger overcomes it.

There’s also a more troubling finding in the same paper: wolves on neighboring, unprotected ranches continued to kill livestock throughout the trials, both before and after the experiments. Fladry seemed to save the specific pasture it surrounded rather than the wolves’ hunger in general.

A Michigan study backs up the pattern
The results from Alberta and Idaho weren’t a fluke. The follow-up study, ‘Testing fladry as a nonlethal management tool for wolves and coyotes in Michigan,' published in Human–Wildlife Interactions in 2010, found that, in the eastern Upper Peninsula of Michigan, the inside of flag-protected pastures was visited far less often by wolves than the open land just outside those same fences, but did not find such a difference for pastures without flags. Coyotes were not deterred by the same flags, suggesting that the wariness fladry induces may be specific to wolves rather than predators in general.

Electrified fladry takes it a step further
Researchers eventually wondered if adding a mild electric charge to the flag line, nicknamed “turbo-fladry,” might bridge the gap that plain fladry leaves open. In the 2010 study in Wildlife Research, electrified fladry was found to be two to ten times more effective than standard fladry at protecting a food source from captive wolves. In a Montana field trial across a dozen pastures, wolves avoided every electrified pasture, while they crossed into ordinary barbed-wire pastures twice. No livestock was lost on either type of pasture during that trial.

The bottom line for ranchers
None of this makes fladry, electrified or not, a permanent fix. It takes real labor to install and maintain; flags get chewed or tangled, and determined, hungry wolves do eventually test their limits. What the research does show is that fladry buys you real, measurable time, weeks to months, and that happens to coincide nicely with how ranchers actually use it: around calving pens, lambing grounds, and overnight holding areas during the particular weeks when livestock are most vulnerable.

For an animal that was hunted to near-extinction across the Lower 48 within living memory, a cheap line of flags that can genuinely change its behavior, even temporarily, could be a tool worth keeping in the shed.