The black-faced honeycreeper, or po'o-uli, is endemic to Hawaii's island of Maui and is listed as "critically endangered/possibly extinct." Of the three known birds discovered in 1998, one died in captivity in 2004 and the remaining two have not been seen since that year. Scientists say the species may already be extinct, but surveys in all areas of potential habitat are needed to confirm this. If any have survived, the population would be extremely small. Habitat destruction and the rapid spread of disease-carrying mosquitoes are thought to be responsible for the species' decline.