In late August, she places each kit in a separate den. She continues to bring them food until they are old enough to hunt for themselves. By fall, when the young go their separate ways, a mother ferret is often weak and thin from the strain of feeding her family all summer. Ferrets reduce prairie dog populations a bit, they have never overkilled their prey. Scientists think there have always been only small numbers of ferrets, but they are not sure why.
Ferrets stay underground most of the day and hunt at night, so they can be hard to spot.
Their tracks show only on mud, snow, or loose dirt, and they rarely leave a trail of droppings. One possible sign of ferrets is a burrow with dirt piled up on its entrance holes. Prairie dogs cover the openings to ferrets' dens in order to trap them inside. The dirt plugs rarely stop ferrets, though, because they are also strong diggers. For years, scientists considered black-footed ferrets to be rare and mysterious.