Islands free from grey squirrels and squirrelpox provide critical refugia for red squirrel populations, with active management required to maintain their grey-free status.
Island red squirrel populations enjoy welfare conditions impossible to achieve on most of the mainland: freedom from squirrelpox infection and significantly reduced competition from grey squirrels. The welfare benefit of maintaining disease-free refugia extends across entire island populations, allowing normal breeding, behaviour, and lifespan. Biosecurity maintenance requires ongoing grey squirrel trapping that involves lethal control — a welfare cost to individual greys that is justified by the protection it provides to red squirrel populations. The rapid recovery of Anglesey's red squirrel population after grey removal demonstrates the direct welfare benefit of active island management.