The New Britain thicketbird or Bismarck thicketbird (Megalurulus grosvenori) is a bird species. It used to be placed in the "Old World warbler" family Sylviidae, but it does not seem to be a close relative of the typical warblers; probably it belongs in the grass warbler family Locustellidae. It is found only in the rarely visited highlands of the island of New Britain in Papua New Guinea. It used to be considered conspecific with the Melanesian thicketbird and the Bougainville thicketbird.