The Cetti warbler is a resident warbler that colonised Britain from continental Europe in the 1970s and has established a substantial breeding population in southern England, demonstrating how climate warming can create new wildlife welfare opportunities.
Cetti warbler welfare is acutely sensitive to winter temperature, as this resident species lacks the cold adaptation of longer-established British residents. Severe winter cold causes population crashes because the species cannot migrate to warmer areas when conditions deteriorate. Reedbed and waterside scrub habitat loss reduces the carrying capacity of suitable wintering habitat. Climate change is broadly positive for this species in Britain but creates vulnerability through increased population size followed by crash events.