WILDLIFE RESEARCH: Wolves take toll on deer in GPS study
Wolves took an early bite out of a pilot study to monitor the travels of white-tailed deer in a farmland-forest transition area of northwestern Minnesota, but the project now is back on track.
According to Dr. Michelle Carstensen, wildlife health program coordinator for the Minnesota Department of Natural Resources, wolves killed six of 16 deer fitted in mid-January with GPS satellite collars; the collar of another deer malfunctioned within days of the capture.
DNR staffers were able to retrieve the collars of the six wolf-killed deer and a seventh deer that died of unknown causes, Carstensen said. The collars also emit a VHF radio signal that can be detected as far as two miles away.
"It was scavenged by predators," she said of the seventh deer. "It could have been poached but we're not sure."
The DNR and the University of Minnesota are partnering on the pilot study in an effort to learn more about the movements of deer in an area with a mix of farmland and forested habitat. The 140-square-mile area near Fourtown and Grygla, Minn., is similar to the core of a minor bovine tuberculosis outbreak that occurred in 2005 near Skime, Minn., a few miles to the north.
Carstensen said the discovery of bovine TB in wild deer raised concerns that a better understanding was needed of how deer use this "transitional" habitat and how they interact with cattle.
That knowledge could reduce the risk of bovine TB and other diseases if it's found that deer have too much access to hay and other cattle feed supplies.
"We're looking at how often deer come in contact with unprotected feed and trying to learn more about that interaction and how much time deer spend directly on farms," Carstensen said.
A helicopter crew rounded up and captured the deer in mid-January, and research crews fitted four bucks and 12 does with the satellite collars. When working properly, the collars log the deer locations every 90 minutes, transmitting the data to a satellite every three days. Carstensen then downloads the data once a week.
The U of M funded the GPS collars at a total cost of about $50,000, Carstensen said.
Carstensen said the first wolf kills occurred in mid-February, after a warm snap followed by cold put a crust on the snow. She said the mortality rate was higher than she was expecting.
"But it was a tougher winter," she said. "We had high snow depths in the woods, and then that crust forms and wolves get the advantage. The deer started breaking through and they just got hammered."
Carstensen said the DNR used baited "clover traps" to catch and collar five new deer in early March, so she now is tracking 12 deer.
Despite the early mortality, Carstensen said the study has provided some surprising insights into deer movements in the area. Some deer stayed within a couple of miles of where they were captured, she said, while others ventured nearly 20 miles to heavily wooded parts of Beltrami Island State Forest.
The females, she said, made the longest moves. With the onset of spring, the deer left the big woods and have returned to more agricultural country.
"Two of the adult males stayed within three miles of where we caught them," Carstensen said. "They'll move more during the rut. I thought it was interesting over the winter that we saw these bigger movements in females."
Carstensen said the study is charting new ground because previous Minnesota studies have focused on deer that live exclusively in forested or farmland habitats. Studies have documented long-distance movements in forest deer, she said, while farmland deer generally stay closer to home.
The deer in this study, Carstensen said, are doing some of both.
"Some are actually following the farmland model and staying within two or three or four miles, and others are making bigger movements," she said. "It's skewed. I think that's interesting, and they make their moves really fast, too -- two days, and they're 14 miles away."
Joao Lima, a University of Minnesota graduate student, will be making occasional trips to the research area throughout the summer to get a closer look at farming activity and how it might be influencing where the deer spend their time. Carstensen, along with Eric Nelson, assistant area DNR wildlife manager in Thief River Falls, will monitor the deer.
Carstensen said the collar that malfunctioned in January, along with a replacement unit that went on the blink in March, may be logging data even though they're not transmitting GPS locations, providing the deer are still alive.
All of the collars are programmed to fall off next April, she said, at which time the DNR will send up a plane to track the VHF signals so the units can be retrieved.
There's no doubt, Carstensen said, that wolves took a heavy toll on the research deer, but the sample size isn't large enough to draw any conclusions about the predators' impact on the area's deer population.
"I would be cautious to say that, just because it's only 16 animals," Carstensen said, "This is a small study that might not reflect mortality in a broader area, but for this area, deer definitely took a hit."
Carstensen said the DNR hopes to eventually post regular updates about the deer and where they're going on its website.
Dokken reports on outdoors. Reach him at (701) 780-1148; (800) 477-6572, ext. 148; or send e-mail to firstname.lastname@example.org.