Black-footed ferrets are back.

Well, almost.

They were once extirpated, or extinct in Canada. Thirty-five ferrets were released from captivity into Grasslands National Park in 2009, the first of a series of annual releases to try and reintroduce ferrets into the wild.

To check in on the lithe, weasel-like creatures, experts look to black-tailed prairie dogs. These creatures make up 90 percent of the ferrets' diet. Where there is food, there will likely be ferrets.

Researchers at the Calgary Zoo's Centre for Conservation Research have been working with Parks Canada to monitor the recovery of black-footed ferrets and study black-tailed prairie dogs. This helps them determine where to release ferrets every year and where best to monitor them.

This slideshow follows a group of researchers as they capture and study black-tailed prairie dogs.