Sometimes, a species' survival hinges on inhabiting an area that isn't theirs. From the ubiquitous brown rat to the seals of Pier 39 in San Francisco and the flying foxes of South Eastern Australia, meet nature's unwelcome guests who've found a way to impose themselves onto new and unlikely environments.

When domestic animals escape into the wild, some revert back to their origins and thrive. From wild donkeys in Bonaire to feral pigs in the Bahamas to the wild horses of Assateague, each has found success by reclaiming ancient codes of social living. But can their new environment sustain them forever?