The buff-bellied mannikin (Lonchura melaena), also known as the sooty munia or Bismarck munia, is a species of estrildid finch found in New Britain and Buka Island. It has an estimated global extent of occurrence of 20,000 to 50,000 km<sup>2</sup>.
It is found in subtropical and tropical dry grassland habitat. The status of the species is evaluated as Least Concern.