There’s been a mysterious drop in the number of endangered black footed ferrets in Arizona. They are the only ferret species native to North America, and researchers think disease, drought and other environmental factors could be affecting their populations. As Arizona Public Radio’s Aaron Granillo reports, the ferrets might not even be around today if it wasn’t for a dog named Shep.

35 years ago, on a ranch in Mettetse, Wyoming, Shep brought a dead animal back to his owner. It looked like a weasel, except for the curious black markings on its face, tail, and feet.

"The rancher had no idea what it was, and took it to the taxidermist and they found out it was a black-footed ferret,” says Jennifer Cordova, a wildlife specialist with the Arizona Game and Fish black footed ferret recovery project.

Cordova says Shep’s discovery revealed the country’s last remaining population of the native ferrets, which were thought to be extinct. A federal effort was launched to protect them, and in 1996, Arizona’s Aubrey Valley near Seligman became a re-introduction site for the animals.

"Aubrey Valley has the highest population of Gunnison’s prairie dog in the state," says Cordova. "Because prairie dogs are the ferret’s main diet, that’s why they chose it for our reintroduction site."

Of the 24-sites in the West, Aubrey Valley is one of only two where prairie dogs haven’t been wiped out by plague. Researchers are now trying to determine if the disease has finally infiltrated the area. Drought, wildfire, the effects of grazing could also be factors as to why the ferret population has plummeted over the last three years.

"And there is a lot of research being done," says Sharon Biggs, who runs a captive breeding program for black footed ferrets at the Phoenix Zoo.

"We have a canine distemper vaccine for them. We have a plague vaccine for the ferrets, and we’re in trials right now on a plague vaccine for prairie dogs," says Biggs. "We’re looking at other carnivores to see what disease they might have. I think all the steps that can be taken are being taken."

Counting them is one of those steps. About 35 people took part in this spring’s black footed ferret survey in Aubrey Valley. It’s called spotlighting because they count them at night. Ferrets are nocturnal, so volunteers use high powered flashlights to catch the emerald green reflection of the animal’s eyes.

Joseph Ortega Junior has been spotlighting ferrets for three years, helping to count and catch them so they can be vaccinated. He’s seen their decline first hand.

"There’s people everywhere, and nobody’s seeing anything," says Ortega.

By 2 am, he still sees nothing. Then, Ortega’s flashlight lands on bright, green eyes in the distance.

"It's still acting like a ferret," says Ortega. Then, the animals stands up. "Oh, It’s a pronghorn. Doggonit."

Just a few years ago, volunteers like Ortega would have “spotlighted” dozens of black footed ferrets by now. So far this year, they’ve only counted two. They'll head out again tonight to Aubrey Valley to search for one of North America’s most endangered animals, while researchers search for answers to their decline.