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Outdoors: Winter takes toll on feral pigs in state

Tim Eisele
Special to The Capital Times  —  3/19/2008 7:20 am

This winter wasn't fit for man nor beast, but it did help to put a dent in the population of one non-native pest: feral pigs.

Feral pigs are exotic, non-native wild animals that are found in the wild most likely because they escaped from farming operations and became established or were intentionally released. They pose significant threats, according to the Department of Natural Resources, to the environment and to agricultural operations.

Feral pigs have been found in at least 12 counties of the state, including Crawford County in southwestern Wisconsin.

There the DNR and USDA Animal and Plant Health Inspection Service (APHIS) Wildlife Services Division concluded a successful winter trapping effort that reduced feral pig numbers by at least two dozen.

APHIS Wildlife Services assists the public and other agencies with agricultural damage and wildlife conflict issues.

Past programs have included a combination of activities, including working with landowners to have them report feral pig activities and shoot feral pigs, organized hunts on properties where landowners request assistance, and trapping.

But the agencies learned that in order to have a successful trapping effort, they can't have a lot of human disturbance on the land. Any human activity sends feral pigs scurrying for undisturbed areas.

Mike Cross, DNR conservation warden in Prairie du Chien, explains that USDA APHIS Wildlife Services is operating under a special permit that allows them to bait and trap feral pigs.

"It is closely scrutinized to determine if the site is active with pigs, so that it is a known site that pigs are using," Cross said. "The landowners cooperated and allow the trapping to take place."

Baiting is closely monitored with a trail camera. Trail cameras are put on trees and take photos whenever an animal passes by, confirming that the site is being used by feral pigs and what times they are coming in to feed.

"The trail cameras told us that the hogs were coming in and nothing else was using the bait," Cross said. "It seems like when the pigs are active in the area, deer and turkeys don't seem to use the same site."

A corral trap was assembled over the course of several days while monitoring the trail cameras to be sure the pigs were still coming in to the bait.

The first catch in the trap, Cross said, caught nine feral hogs. The pigs were all in the 90-pound range, not real huge, but they were comprised of four sows (females) and six boars (males).

At a second site, the same approach was used and four more feral pigs were caught, including two boars and two sows.

In total at least 25 feral pigs were eliminated, and some of the sows were carrying fetuses.

"It's a little like deer management, if you remove the females, the sows in this case, the reproductive capability is gone," Cross said. "The property owners were very supportive of these efforts, because a lot of this area was on cropland. In fact last year one farmer had substantial feral hog damage to crops and had to replant between 15 and 30 acres of corn."

It also appears that deer have now moved back into the areas once the feral pigs were gone, which seems to indicate that competition exists between the feral hogs and wildlife.

Part of the reason for the success was the hard winter and abundant snow, which Cross believes had the feral pigs almost "yarded up." They moved back and forth from where they bedded down to where they fed, and did not travel as extensively as they normally do other times of the year.

The other key component was that landowners were willing to curtail other uses of the land in order to allow the trapping efforts to be carried on. Any human disturbance in the area could have moved the feral hogs out to other areas.

Cross credits USDA Wildlife Services for spending a lot of time, effort and research on the problem.

"We monitored and checked traps daily and when we felt the time was right we set the traps," said Barb Bodenstein, wildlife disease biologist with USDA APHIS wildlife Services in Sun Prairie. "We'll be primarily monitoring again during spring, summer and fall, and encouraging landowners to report any observations of feral pigs or damage to the DNR."

Wildlife Services took blood samples from the feral pigs and is having them tested for pseudo-rabies, swine brucellosis, and classical swine fever. So far, Bodenstein said that all of the blood samples have come back negative.

Tim Eisele
Special to The Capital Times  —  3/19/2008 7:20 am