Archaeology and Invasive Species: The Chirikof Island Project

Authors: Catherine West | Boston University | and Courtney Hofman | University of Maryland; Smithsonian Institution

How long have ground squirrels lived on Chirikof Island?  Were they native to the island, taken there by Native people, or are they a recent introduction? A team of researchers from Boston University, the University of Maryland, and the Smithsonian Institution asked these questions after a trip to the island in the summer of 2013 with the Chirikof Island Project. Chirikof is managed by the Alaska Maritime National Wildlife Refuge (AMNWR), and many AMNWR islands are under threat from landscape degradation and invasive species introductions – on Chirikof, cattle, Arctic foxes, and ground squirrel are considered introduced, invasive species. The introduction history of both cattle and Arctic fox on Chirikof is clear, but the ground squirrel’s history is not well understood. While it has long been thought that Russian traders or American settlers introduced the ground squirrel as an economic resource, our 2013 archaeological excavations recovered squirrel bones from prehistoric sites. We hoped we could answer our questions – and address whether this species should be considered “invasive” – by doing two things: 1) by dating the archaeological squirrel bones, could we tell how long ground squirrels have been on Chirikof? And, 2) by looking at the ancient DNA (aDNA) in the archaeological bones, could we tell if the ancient squirrels were related to the squirrels living on the island today?

Chirikof’s Arctic ground squirrel (Urocitellus parryii). Photo by Patrick Saltonstall.

Chirikof’s Arctic ground squirrel (Urocitellus parryii). Photo by Patrick Saltonstall.

People have lived on Chirikof Island for at least 5000 years, and the archaeological record suggests this was a crossroads for people traveling from the Aleutian Islands, the Alaska Peninsula, and the Kodiak archipelago, though occupations were intermittent (Saltonstall and Steffian 2005). The Russian American Company established an artel for hunting ground squirrel and making parkas in the mid-nineteenth century – Alutiiq and Unangan people in this region used ground squirrels to make parkas, which they still do today. After the Russian occupation, Americans established both Arctic fox and cattle ranching in the late nineteenth/early twentieth century. Today the landscape shows the effects of cattle and fox introductions through severe erosion and diminished waterfowl and seabird populations (

Catherine West excavating 2000-year-old midden on Chirikof’s west side. Photo by Samantha Dunning.

Catherine West excavating 2000-year-old midden on Chirikof’s west side. Photo by Samantha Dunning.

Our research has produced exciting results! To answer our questions about the ground squirrel introductions, we collected ground squirrel bones from coastal middens on Chirikof. We were able to radiocarbon date the bones and to analyze their ancient DNA, which suggests that some of the archaeological squirrel bones are 2000 years old and that the squirrels living on Chirikof today are direct descendants of those living there 2000 years ago. While we don’t yet know if Native people took the squirrels to Chirikof or if the squirrel is native to the island, we can ask the questions: what does it mean for management and eradication if these animals were introduced prehistorically? And, how old is old enough for an introduced species to become a “natural” part of an island environment? This long-lasting population has thrived in this isolated, stormy place for thousands of years, so the next step in this project is to try to figure out where the Chirikof Island ground squirrels came from and to work with AMNWR to understand their place in the island’s ecosystem.

This work is funded by the National Geographic Society, Boston University, and the Smithsonian Institution.

Chirikof’s introduced cattle. Photo by Patrick Saltonstall.

Header image: Chirikof’s introduced cattle. Photo by Patrick Saltonstall.


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