Raven control programs see reduced numbers, depredation in southwest Wyo
Evanston – “Ravens have been an economic and ecological problem causing damage,” says Dan Madsen, a certified crop adviser in Fremont County. “We have a five-county raven control program that was spurred by larger entities and weed and pest districts.”
With municipalities, large companies, livestock producers and more expressing concerns over the detrimental impact seen by ravens, particularly in southwest Wyoming, efforts have been put in place to attempt to control the populations.
“I’ve been dealing with predators most of my life,” says Rod Merrell of USDA Wildlife Services. “In southwest Wyoming, in my opinion, ravens are probably as damaging as any vertebrate that we have, as far as their impacts on livestock production, wildlife and human health and safety.”
“Raven populations have increased in Wyoming, especially in southwest Wyoming, by as much as 1500 percent since 1960, this sharp increase is likely due to these highly-adaptable birds taking advantage of human made resources.” Merrell says, noting that area sheep producers in particular have seen dramatic impacts.
Beginning in the 1990s, Merrell notes the first documentation of predation by ravens on lambs occurred.
“Predation has escalated considerably over the years,” he continues.
Ravens kill livestock by pecking at the eyes and umbilical cords of newborn lambs and calves.
“The newborn animals either bleed to death or die of shock,” Merrell says. “The first documentation of depredation in calves was in 2005 in Uinta County. It has become an even bigger problem now.”
While losses are difficult to quantify, Merrell says they are considerable, and complaints from cattle producers have escalated dramatically in recent years.
In addition to depredation, ravens create health and human safety issues at industrial facilities because they congregate in such large numbers.
“Ravens have escalated in industrial facilities, and their roosts are huge in some places,” Merrell says. “We’ve seen roosts with as many as 300 birds.”
The resulting fecal matter creates bacterial concerns, among other safety issues. At the same time, removal efforts are both expensive and time-consuming.
Because ravens are regulated under the National Migratory Bird Act, state wildlife agencies have very little control over populations.
“In April 2012, the Wyoming Game and Fish Department requested lethal control of ravens at four locations in southwest Wyoming,” Merrell notes.
The U.S. Fish and Wildlife Service has the authority to grant permits to control migratory birds, such as ravens, for a variety of reasons, including reducing incidence of livestock depredation and to reduce the risk of livestock disease.
“The other reason we went after this project is to help alleviate human health and safety concerns from raven roosts and nests,” Merrell explains.
“We started a control project encompassing Fremont, Sweetwater, Sublette, Lincoln and Uinta counties,” he adds.
The project includes 10 large roosts and locations at landfills across the southwest part of the state with the goal of reducing populations.
“We aren’t trying to eradicate the species,” Merrell clarifies. “We are just trying to bring population numbers back down to normal levels.”
Using a site-specific methodology, Merrell notes that ravens were targeted with an avicide called DRC-1339.
“We went out to landfill sites prior to placing bait to count the ravens,” he says. “Then, we take high-speed photographs and count the birds on the computer. It works quite accurately.”
After counting birds, appropriate avicide levels are determined.
“We acquired supplemental label use so we could use dog food as the carrier,” Merrell also notes, adding that typically, meat baits are utilized as the carrier. “Meat baits are extremely labor intensive and not as effective.”
Additionally, FWS also approved the use of DRC-1339 for human health and safety, whereas in the past it was only available for use for livestock depredation.
After applying the bait, the remaining population of ravens was estimated by the same method to calculate initial populations. Take numbers must be reported to FWS.
“It is difficult to calculate take because it takes 24 to 72 hours for the ravens to expire,” Merrell says. “Take numbers are also reported by environmental specialists at industrial sites, so we can get an accurate reflection of take.”
In the first year of the project, Merrell notes that numbers were reduced.
For example, in the Rock Springs landfill, 330 ravens were counted in 2013. The following year, approximately 130 birds were counted. In the Green River landfill, 65 birds were noted in 2013, and 60 were counted in 2014.
“There is an interesting phenomenon between Green River and Rock Springs,” Merrell explains. “I’m quite certain the birds were utilizing both landfills.”
In Kemmerer in 2013, well over 200 birds were counted, and only 20 were identified in 2014.
“We can’t attribute the entire population decrease to the avicide,” he continues.
Numbers nearly halved in the Big Piney landfill, and decreased from 150 to 90 in Farson.
In Fremont County, raven populations were more consistent from 2013-14, but Merrell also notes that retention of young ravens was very good following treatments.
Additionally, bait application was later in the year as a result of permit delay times, which may impact effectiveness.
“These numbers represent reductions of the population from 31 percent in 2013 to as high as 68 percent population reduction in 2014,” Merrell said. “If we count the overall number of birds surveyed, there was a 40 percent reduction in populations. We believe this is a very conservative estimate.”
Merrell also notes that direct benefits were seen as a result of the project.
“Livestock depredation dropped 79 percent in 2013, and depredation was almost non-existent in 2014 compared to what had been seen in the last 15 years.”
Additionally, complaints from the industry about human health and safety concerns dropped 100 percent as a result of the project, with no complaints in 2014.
With the hope of continuing to positively impact raven populations, Merrell says they hope to be consistent with their treatment to bring birds back in line with acceptable numbers.
“I’m confident we are going to have to continue treating because of the prolific nature of ravens,” Merrell comments. “We will continue to apply at some level or another.”
Sage grouse benefits
Raven control is suspected to benefit sage grouse populations, as well, says Rod Merrell of USDA’s Wildlife Services.
“Studies have shown that overpopulation of ravens can have negative impacts on sage grouse populations,” he says, noting that most studies are relatively recent. “It is proven that ravens definitely have an impact.”
“We are doing studies now on the benefits for sage grouse,” Merrell says.
A study is currently being conducted in Fremont County using 40 artificial nests.
“We use brown chicken eggs in the same habitat as sage grouse nests, and we place trail cameras to identify what destroys the nests,” he says. “Out of the 75 percent of nests that were destroyed, ravens were 80 to 85 percent of the problem.”
Magpies were the next leading cause of nest destruction.
“After we started treating Fremont County’s landfills, we saw a 64 percent decrease in nest destruction in 2013 and 68 percent reduction in 2014,” Merrell adds.
Madsen and Merrell addressed the 2014 Wyoming Weed and Pest Annual Convention in Rock Springs.
Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at firstname.lastname@example.org.