Arctic foxes are endangered in Sweden, Norway and Finland, scattered in isolated populations that can fall victim to severe inbreeding, further threatening their survival.

That’s what happened to a group descended from six white foxes that settled in the early 2000s on Helagsfjället, the highest mountain in southern Sweden.

But in 2010, a local ranger noticed something different: slate-colored or “blue” Arctic foxes, which had to be newcomers. The immigrants presented a rare opportunity for scientists to study what happens when new genetic material flows into a small, isolated population threatened with extinction.

In a study published Wednesday in Proceedings of the Royal Society B, scientists from Sweden and Norway reported that just three new males dramatically reduced inbreeding and produced a generation of more robust offspring in the Helagsfjället arctic fox population.