By: Sam Cook, Duluth News Tribune
A gray wolf walks through an opening in the forest north of
Duluth on Wednesday morning. A pilot with the Minnesota Department of
Natural Resources located the wolf from the air after listening to its
radio-collar signal. The DNR uses aerial observations to provide data
for a wolf population survey in progress this winter. (Bob King /
rking@duluthnews.com)
He knows what he’s up against. “Trying to count wolves is a challenging thing,” Erb said. “When you’re talking about 30,000 square miles (of wolf range), and it’s a secretive animal, there are always going to be uncertainties.”
But he believes the DNR’s survey methods are sound and that the state’s wolf population estimates are good. “I do believe it’s been a very useful and reasonably accurate method,” Erb said.
Some Minnesotans aren’t as comfortable with the DNR’s last estimate of 3,000 wolves, within a range of 2,200 to 3,500. “The last survey indicated a range of 2,200 to 3,500. They give us a broad range,” said Howard Goldman, Minnesota state director of the Humane Society of the United States. “We’re saying this is much too imprecise a process.”
The Humane Society opposes wolf hunting and trapping in Minnesota. Mark Johnson of the Minnesota Deer Hunters Association believes the DNR is “still on the learning curve with its population estimates and surveys” of wolves. “I think it’s a pretty good process,” Johnson said. “They’re using the best science available, but could it be better? Yeah.”
The deer hunters’ group has been a strong advocate for wolf hunting and trapping seasons in Minnesota.Public interest in the current wolf population survey is high, especially now that the state is holding an annual wolf hunting and trapping season. And the Minnesota Legislature is considering a bill that would put a five-year moratorium on wolf hunting and trapping.
Last fall, hunters and trappers took 413 wolves in the state’s first season after the gray wolf was removed from the federal Endangered Species List in January 2012. Opponents of the wolf hunt are concerned that the combination of hunting harvest, wolves killed in depredation cases and illegal taking might not be sustainable in the long term.
Determining wolf range
Minnesota’s method for counting wolves includes three elements.
First, biologists try to determine the boundaries of Minnesota’s wolf range, especially how far south and west wolves live in the state.
To do that, the DNR relies on the field observations of natural resources employees from the DNR, U.S. Fish and Wildlife Service, U.S. Forest Service, tribal biologists and others. Observations start in November and continue until the snow melts.
Observers are looking for any sign of a wolf or wolves — an actual wolf, wolf tracks, wolf scat, a wolf or wolves howling, a wolf-killed deer. The observer notes where it was and how many wolves were estimated to be there. A pair or more is considered a pack.
After total wolf range is delineated, DNR biologists then estimate what areas within that range are occupied by wolf packs. If winter wolf observations confirm a wolf pack within a township, it is considered occupied.
Not all areas can be searched due to access and other logistics, so the DNR uses a wolf habitat model to evaluate whether wolves are likely to occupy some other townships where surveying did not take place. Collectively, this provides an estimate of the number of square miles used by wolf packs. From the 2007 survey, that was estimated to be about 28,000 square miles.
How many packs are there?
Once biologists estimate the volume of wolf range occupied, they try to determine how many packs occupy the area. Erb compiles data on wolf pack territory size using signals from wolves collared throughout the state by the DNR and others such as University of Minnesota researcher L. David Mech. Going into this past fall, about 50 wolves were radio-collared, representing about 40 packs. (Sometimes more than one wolf from a pack is collared.)
Some collars transmit GPS locations of wolves to satellites, while locations from others are obtained from aircraft. Erb and others can then plot the locations on maps. By tracking a pack’s movements, biologists can learn the size of a pack’s territory.
The most recent surveys indicated an average territory size of about 40 square miles, just more than the size of a typical township. Deer density and competition among wolves are key factors that determine how much space a wolf pack needs or can defend.
“If we know the occupied range (of all wolf territory) was 30,000 square miles, and we know each pack uses so many square miles, that’s how we get our estimate of the number of packs,” Erb said
The estimated number of packs for the past two surveys has been about 500, Erb said.
How many wolves per pack?
The last piece of the puzzle is learning how many wolves live in each pack. To determine that, researchers in airplanes make repeated flights through the winter to locate the radio-collared wolf (or wolves) in each pack. Researchers then see how many other wolves are traveling with the radio-collared wolf. The average for these radio-collared packs is then used as the estimated pack size for all packs. “If the average pack size is five and we have about 500 packs, then you’d have about 2,500 wolves,” Erb said.
But researchers know that not all wolves are in packs. Always, some lone wolves are roaming the wolf range looking for another wolf to pair up with, Erb said. Research in several areas has indicated that 10 percent to 20 percent of any wolf population is made up of these lone wolves. “So we add an additional 15 percent to whatever our total was,” he said.
The agency conducts a wolf population survey every five years, and the population has been relatively stable for the past 10 years, Erb said. Other annually collected track survey information is used to assess population changes in between periodic population estimates. Preliminary results of the current survey will be available by early summer, he said.
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