THE WISCONSIN DEPARTMENT of Natural Resources released this photo in April 2019 it said was poisoned ground beef balled up and intentionally planted to harm wildlife. (Wisconsin Department of Natural Resources photo)

Someone is leaving poison out along the roadside on public lands in northern Wisconsin, authorities say, killing pet dogs and wildlife.

Four dogs have died in the past month in Forest County near the Michigan border. Testing on two of the pets, a 4-year-old yellow Labrador retriever that died Friday and a 3-year-old German shepherd that died April 1, confirmed that they died from poisoning. Two more dogs died this past weekend and tests are pending.

Officials believe the deaths are related to the ongoing poisonings in Florence, Forest and Marinette counties that have been investigated for about a year, WLUK-TV reported. So far, seven pet dogs have died; all are thought to have been poisoned on public land.

The U.S. Fish and Wildlife Service is offering a $1,000 reward for information that leads to an arrest in the case. Tina Shaw, a public affairs officer with the U.S. Fish and Wildlife Service’s law enforcement division, said the poison also has killed other animals in the area including coyotes, weasels and wolves.

“What causes someone to do this is perplexing to all of us,” Shaw said.

Shaw said the poison is left near roads in public places. The dogs that died earlier in April both were being walked on a leash by their owners.

Before the most recent deaths, there had been at least two confirmed poisonings of hunting beagles in Forest County and more wildlife mortalities in Marinette County, Shaw said.

Shaw said she hopes the reward will help spur members of the public to come forward with tips. She also said it’s important for people in the area to be aware of the risks as they take their own pets out.

“Concerned citizens can crack cases,” Shaw said. “We definitely want to close the case, but we also really need to increase awareness about what’s happening right along the roadsides and on public land.”

Anyone with information about the recent wildlife and dog deaths can call the U.S. Fish and Wildlife Service’s Office of Law Enforcement at 608-221-1206.