By ice, not boat? Rethinking prehistoric wolves on a Baltic island

How did grey wolves (Canis lupus) reach Stora Karlsö, a small Baltic Sea island near Gotland? A recent archaeological study proposed that two prehistoric wolves found on the island, one Neolithic and one Bronze Age, had been transported there by people. In a new letter in Proceedings of the National Academy of Sciences, Luc A. Janssens and L. David Mech argue that natural dispersal over winter sea ice is the more plausible explanation.

The original interpretation pointed to the island setting, a marine-rich diet, apparently small body size, and a possible limb pathology as evidence of human control. Janssens and Mech revisit each of these claims.

Although Stora Karlsö lies about 80 km from mainland Sweden, Baltic ice has historically linked the region in winter, and wolves have been documented travelling more than 150 km across frozen Baltic waters.

Wolves reaching the island could also have hunted its abundant maritime fauna. Modern wolves are known to prey on marine mammals, including seals, while isotope values from one specimen do not closely resemble a human-associated diet.

The Bronze Age wolf may not have been unusually small either. Estimated at about 32 kg from its humerus, it falls within the normal wolf size range. Likewise, the minor bone lesion previously interpreted as evidence of disability would not necessarily cause lameness, weakening the case that the animal required human care.

The authors further note that the two wolves lived roughly 1,600 years apart, during very different cultural periods. Interpreting both as human-transported animals would require two independent episodes of wolf management or taming, despite no comparable evidence from prehistoric Scandinavia.

Rather than demonstrating human transport, the authors conclude that the available evidence better supports wolves naturally crossing sea ice and exploiting the island’s coastal resources.

Reference

Janssens, L. A., & Mech, L. D. (2026). Did Stora Karlsö wolves reach the island naturally or by boat? Proceedings of the National Academy of Sciences, 123, e2607054123. https://doi.org/10.1073/pnas.2607054123