Steven Hogg grew concerned when he realized it had been awhile since he had seen — or smelled — a dead skunk.

Not everyone would consider that a problem. But to Hogg, wildlife supervisor for the Plymouth-based Three Rivers Park District, a lack of contact with striped skunks in the parks could suggest a decline in local populations of the aromatic mammals.

“I wondered, are striped skunks a part of our parks anymore?” he said. “Anytime you’re missing something from the environment, I think that is at least a reason for concern.”

So Hogg decided to conduct what’s called a camera trapping program. Launched in 2017, the project uses digital cameras, rather than physical traps, to capture images of animals in the wild.

The cameras are equipped with motion detectors that trigger their shutters, so they photograph anything that crosses their lenses. They also are equipped to take pictures in the dark.

Volunteers, or “citizen scientists,” regularly venture deep into seven Three Rivers park reserves around the west and south metro area, strap the cameras around trees and return every three weeks to collect the images and move the cameras to different locations. The project covers wide swaths of territory and produces tens of thousands of photos a year.

Over the program’s three years, the cameras have captured coyotes, raccoons, wild turkeys, two kinds of fox, three kinds of squirrels, opossums, minks, owls, bats, a 4-foot-tall sandhill crane and its baby (called a colt) and thousands of deer — bucks, does and fawns.

Hogg was particularly interested when a photo was shot of a fisher, a member of the weasel family, because historically the animals have lived in northern Minnesota.

The citizen scientists enjoy the project, Hogg said. “A lot of them are retired, very fit, and want to get outside,” he said.

Cheryl Batson, a volunteer from Brooklyn Center, is a nurse by profession but loves working outdoors.

“When I was having to make my career choice it was like, do I want to do something that is outdoors or do I want to help people? In the end I chose people,” she said. “But that doesn’t mean I can’t have this as my hobby.”

Mike Sweet, a biologist who retired from the U.S. Fish and Wildlife Service in 2012, was so interested in recording wildlife that he already had been setting out his own cameras before becoming involved in Hogg’s project. He said he’s hoping for “one of those rare instances of a mountain lion coming through, or a bear.”

Hogg is interested in mammals in general. Birds, amphibians and reptiles are relatively easy to track without cameras, he said, but “mammals are very secretive.”

For instance, he can identify birds by their songs. But when he hears coyote howls at night, other coyotes don’t always respond — perhaps desensitized to noise coming from housing springing up around the parks.

Pictures have been taken of a few members of the ape family — specifically, humans — wandering off the trails against the rules, sometimes grinning boldly into the camera lens.

As for striped skunks, the numbers captured on camera have sharply declined. The first year, there were 24 skunks spotted on almost 20,000 photos. The second year, though the total photos more than doubled as more volunteers participated, just one skunk was found. Last year, the number was zero.

Though that would seem to confirm Hogg’s fears, he stressed that it’s too soon to draw conclusions. Numbers of all the animals photographed swing up and down from one year to the next, so fewer photos don’t necessarily indicate a declining population overall; that could have more to do with camera placement or other factors. Larger patterns can’t be detected without comparing figures over many years or even decades.

“We need to be very careful with trying to interpret anything,” he said “This is very short-term data.”

Rather than measuring what’s not there, the project is better for finding what is. Some critters appear unexpectedly, like the fisher. Hogg is hoping a bobcat will pop up someday. Without the cameras keeping watch, he said, “We don’t know if we have rare species here.”