They live in unused prairie dog holes, or they kill and eat the owner of the hole and then move in. They move around a lot, from burrow to burrow, hunting for prairie dogs. They sometimes travel more than a mile each night. They leave scent to mark their territory which averages 150 acres for a female with a litter. They live alone except during the breeding season, and even then the males and females only stay together until breeding occurs.
Biologists study black-footed ferrets at night, usually with the help of spotlights.
A ferret's eyes glow bright green in the dark, and that's how biologists find them to count them. Ferrets spend a lot of time underground, and their eye shine is hard to see unless they are looking directly at the biologist. As a result, ferrets are always hard to find. Other ways to tell if black-footed ferrets are around is to watch the snow for tracks or trenching. Black-footed ferrets can't throw dirt between their legs like dogs when they are digging.