For the first time in more than 70 years, black-footed ferrets (Mustela nigripes) are now living wild on Canadian soil. Last Friday, the Toronto Zoo released 34 black-footed ferrets into the prairies of Grasslands National Park in southern Saskatchewan near the U.S. border. The endangered species—once "probably the rarest mammals on Earth," according to the Black-Footed Ferret Recovery Program—disappeared from Canada in 1937, and was thought to have gone completely extinct around 1974.

About half of this batch of released ferrets were born in the Toronto Zoo's ferret breeding program, and then temporarily transferred to a similar facility in the U.S., where they had a chance to practice their hunting and survival skills in a controlled environment before being released into the Canadian wild.

It's been a long, dangerous few decades for the black-footed ferret. The chance discovery of the world's last population of around 130 ferrets near Meeteetse, Wyo., in 1981 kicked off a long conservation saga that has now led to successful reintroductions in eight U.S. states, Mexico and now, at last, Canada.

It almost didn't happen. Soon after its discovery, the Meeteetse population was devastated by canine distemper and sylvatic plague (that's a variation of bubonic plague, by the way). The world's last 18 M. nigripes were captured between 1985 and 1987, and formed the core of a breeding program that today finds the species's numbers at around 1,000 individuals, a quarter of which now live in the wild.

Human settlement of North American prairies kicked off the black-footed ferret's extinction crisis. In addition to importing the deadly canine distemper and sylvatic plague, farmers had transformed the prairie landscape on which the ferrets relied. In the process, much of North America's prairie dog population disappeared, leaving the ferrets without their main source of food.

Luckily for the Canadian ferrets, their new home is not only abundant with prairie dogs, it is also currently plague-free.

This is just the start for the Canadian population. Another 30 to 40 ferrets will be released into the wild annually for the next few years.

Image: Black-footed ferret, via U.S. Fish & Wildlife Service