The Invasive Squirrel That Wasn’t

Everyone thought that the Arctic ground squirrel was an invasive species on this remote Alaskan island. A pair of scientists beg to differ.

Turns out, the Arctic squirrels (Urocitellus parryii) on Chirikof Island, long believed to be an invasive species, were native. Ianaré Sévi/ Wikimedia

Treeless, wind-swept Chirikof Island has suffered from many ecological woes. Eighty miles Southwest of Kodiak Island, this currently uninhabited Alaskan island has been plagued with invasive species that threaten the native ground-nesting birds: Namely, Arctic fox, feral cattle and Arctic ground squirrels. But suddenly, scientists are looking at the squirrels and questioning that assumption.

Back in the 1800s, demand for furs led Russian and European settlers to trap live Arctic foxes from much farther north and release them on islands where they could be ranched for money. But those relocated foxes would need food, and so settlers brought along ground squirrels. At least, that's how the story goes.

“People had been observed taking big barrels full of live squirrels and releasing them elsewhere on other islands,” says Catherine West, a Boston University archaeologist who did her post-doctoral work with the Smithsonian's National Museum of Natural History and recently co-authored a study investigating the origins of the ground squirrels.

Land managers had long assumed that both foxes and squirrels were invasive species on Chirikof Island. The last of the foxes were trapped and removed from the island in 2015. At some point in the future, removal of the squirrels might have become a priority because of their tendency to impact vegetation and native seabirds in what appears to be a negative way. But West and her colleagues have discovered that everyone had the squirrels all wrong.

“When I went there for the first time for a survey we went to check on some [Native American archaeological] sites because they are eroding . . . we all thought that squirrels and foxes were a historic introduction . . . and we found squirrel bones in an ancient midden. And we said: 'this isn't what we expected.'”

The middens are filled with discarded bones, shells, broken artifacts and anything else that was unwanted by the Native Americans who have lived in the region for at least 5,000 years. If the ground squirrels were an invasive species brought to the island in the 1800s, then what were their bones doing in the middens of people who pre-dated western contact?

“The middens are just dumps of refuse that we can associate with humans,” says West. “It's where people threw all their trash. And that's where I go in and dig a very systematic hole and screen everything.”

West worked with lead co-author Courtney Hofman, an anthropologist from the University of Oklahoma, to gather and process samples for radio carbon dating and genetic analysis. Their research was funded in part by the Smithsonian Conservation Biology Institute.

Their conclusions were twofold. First, ground squirrels have been living on Chirikof Island for at least 2,000 years. Second, today's squirrels are the direct descendants of those native squirrels.

“The stuff I can see [in the middens] is on top and is younger,” says West. “In any of these sites, I never found anything older than 2,000 years.” Settlements were usually built along the coast and the oldest middens may have already disappeared into the sea. “The island has been eroding since the ice retreated about 14,500 years ago.”

The wild cattle were first introduced to provide food for the caretakers of the foxes. Today they number around 700. While they are without question an invasive species that is harming the island's ecosystem and trampling nests, they may also represent the last of a heritage breed and the idea of removing them remains controversial.

The U.S. Fish and Wildlife Service, which manages the island as part of a federal wildlife refuge, defines an invasive species as “one that is not native to an ecosystem and which causes, or is likely to cause, economic or environmental harm or harm to human health.”

“My problem with this is that there is no temporal aspect of this,” says West. After how many years can a species be considered native? Hundreds? Thousands? Does it matter whether human activity or other circumstances moved the species around? Does it require new adaptations to the new environment rather than just a set period of time? These are big questions that U.S. Fish & Wildlife's definition does not address and which ethicists and scientists will likely debate for a long time.

“I'm not a biologist. I wanted to see how my perspective as an archaeologist might fit into this,” West says.

That archaeological perspective might have given the Arctic ground squirrel a new lease on Chirikof Island.

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