As elk head for winter grounds, wolf-related moose mortality spikes, researchers find.
By Mike Koshmrl, Jackson Hole, Wyo.
February 13, 2013
Wolves roaming the north end of Grand Teton National Park have developed an appetite for moose during the wintertime, a study shows. Some 43 moose, including 25 cows, were found wolf-killed by Grand Teton and U.S. Fish and Wildlife Service researchers during the winters of 2010 and 2011. Preliminary data shows another 13 were killed during 2012, Grand Teton biologist Steve Cain said.
Wildlife officials have been dealing with a Jackson Hole moose herd in decline for years.
An exchange of emails between Park Service and Wyoming Game and Fish Department officials shows the study findings surprised biologists. “Wow, I don’t think anyone can argue that wolf depredation on moose is not additive and that they are not having an effect on moose numbers,” Game and Fish large carnivore biologist Bob Trebelcock wrote in a May email.
Grand Teton biologist Sarah Dewey responded: “I agree that the number of moose kills is interesting. I think it reflects what is available to these packs and what in at least one heavy snow year was vulnerable. In 2011, emergency feeding was done in Buffalo Valley, which pulled a lot of the wintering elk up there.” The two packs studied were the Phantom Springs and Pacific Creek packs, which each numbered 13 animals in year-end 2011 counts.
The packs were chosen because their home ranges are free of elk feedgrounds.
In addition to the 43 moose killed during the first two winters of the study, the packs killed 58 elk and four deer. Predation dynamics in the summer differ significantly because of prey availability and risk, Dewey said in an interview.
“We’re close to the population objective for elk and have a lot fewer moose,” she said, referencing the 11,900 elk last tallied in the Jackson herd. “Elk are easier for them to go after. They’re both still risky for them to attempt to kill, but being a little bit smaller animal, there’s a little bit less risk with the elk.” The two packs subsisted almost entirely on the smaller species during the summer, eating a diet of 93 percent elk.
Elk occupy the northern reaches of Grand Teton National Park and surrounding national forest in high densities during the warm seasons, but they migrate south when the snow flies. They mostly winter on the National Elk Refuge and on state-run feedgrounds in the Gros Ventre drainage.
The Jackson Hole moose herd is less than a fifth the size it was 20 years ago, Game and Fish “job completion reports” show. The population, estimated at 919 at the last count, is about quarter the department’s objective of 3,600.
Reasons for the local decline are a matter of debate, but they are thought to include climate change, wildfire-scarred landscapes, parasites and increased abundance of large predators. “There’s a lot of pressures on moose right now,” Dewey said. Moose getting hit by vehicles has been one factor in the decline. Nine moose were killed on park roads last year, and Highway 390 has been a hotspot for moose deaths over the past several winters.
Herdwide road kill counts are not currently available, but they are being assembled by the Jackson Hole Wildlife Foundation, executive director Leigh Work said. Game and Fish officials in charge of managing the moose herd weren’t dismissive of the effects of wolf predation. “Any mortality on the reproductive sector [of the moose herd] is something that we have to contend with,” Game and Fish biologist Doug Brimeyer said.
In mild winters, Brimeyer said, the feedground system could be a cause of increased wolf predation on moose. “Feedgrounds do pull elk down onto localized areas,” he said, “but if they didn’t pull the elk down we’d be dealing with other problems. In a more severe winters, those elk would leave those areas also,” Brimeyer said. “Before wolves were there, I witnessed mass movements out of the the Buffalo Valley.”