The Common Murre Uria aalge is listed as an endangered species in Japan and breeds only on Teuri Island, Hokkaido. The Teuri Island population has decreased from 8,000 birds in 1963 to 19 in 2010. They bred on sea-stack and cliff ledges (open habitat) before 1994, but mostly in cliff caves (closed habitat) after 1994. In closed habitat, the fledging rate was greater and the rate of population decrease was smaller than in open habitat. Restoration actions (decoys and sounds) were effective in attracting murres, but did not enhance the fledging rate sufficiently to raise their population, possibly because of predation by avian predators (Slatybacked Gulls Larus schistisagus and Jungle Crows Corvus macrorhynchos). Using the fledging rate observed in closed habitat and other demographic parameters found in references, Population Viability Analysis shows that the probability of extinction of the Teuri population within 50 years is 66%. To improve the fledging rate and make the restoration actions more effective, we recommend the control of avian predators.