Wolves, usually young adults, which decide to leave or are driven from their pack are called "dispersers". Commonly known as lone wolves, they are on the lookout for either a new pack which will accept them or for suitable habitat not already claimed by a pack. Occasionally, such dispersers from Canadian packs near the U.S. border explored what appeared to be promising territory to the south. There were sporadic reports of such natural reintroductions through the 1970s, but the wolves didn't fare well and were unsuccessful in establishing packs.

The wolves which journeyed to Isle Royale were a remarkable exception.

The first successful natural reintroduction of wolves to the Lower 48 was a direct result of the severely cold winter of 1948-49, when wolves from Ontario ventured across 15 miles of frozen Lake Superior to reach Isle Royale National Park in Michigan. The wolves and moose (the island's only large prey species) are the basis of one of the longest-running studies of predator/prey relationships in the world.

The second successful natural reintroduction of wolves occurred in the early 1980s, when Canadian wolves crossed the border into Montana seeking new territory in Glacier National Park. In that protected wilderness they found sufficient prey and were able to prosper as a pack. Their appearance helped fuel a spark in the public's imagination - the idea that wolves could and should live in America's national parks. Those dispersers helped lay the groundwork for the most successful and best known reintroduction program in the world - the return of the wolf to Yellowstone National Park.