Re-introduction of the red squirrel into Newborough forest on the island of Anglesey, UK

Summary

Red squirrels (Sciurus vulgaris) went extinct in Newborough forest, a 770 hectare coastal pine plantation on Anglesey, Wales, in the mid-1990s after invasive grey squirrels (Sciurus carolinensis) colonized the island and spread squirrel-pox virus. Menter Môn, the Centre for Ecology and Hydrology, and the Welsh Mountain Zoo began systematic grey squirrel eradication in 2002 while building a captive red squirrel colony from genetically screened stock supplied by the Zoological Society of Wales in five woodland enclosures built in 2003. Following a small trial release of three radio-tagged adults in May 2004, twenty captive-bred red squirrels were soft-released into the forest between 2004 and 2006, supported by nest boxes and feeding stations. The trial female produced two litters within six months, and adult survival ran 67 to 78 percent, apart from a 2005 viral outbreak that killed several captive adults and, in 2007, an unexpected adenovirus that killed three juveniles. By May 2007, three years after the first release, live trapping found 13 breeding females and five wild-born litters spread across an expanding area of the forest, though up to ten grey squirrels persisted despite ongoing control, pushing island-wide eradication back to a 2010 target. The project rated itself Successful, having established a productive, self-reproducing wild red squirrel population through soft-release methods, while acknowledging that incomplete grey squirrel eradication remains an unresolved disease risk.