The Bismarck Thicketbird (Megalurulus grosvenori) is a bird species. Previously placed in the in the "Old World Warbler" family Sylviidae, it does not seem to be a close relative of the typical warblers; probably it belongs in the newly-recognized grass-warbler family Megaluridae. It is found only in the rarely visited highlands of the island of New Britain in Papua New Guinea.
This little-known species was for long classified as a data deficient species by the IUCN, due to the general lack of reliable data on its distribution and numbers. While there have been no records since its discovery in 1959, recent evidence suggests the habitat destruction in the Bismarck Archipelago presents a greater risk than previously believed, leading to the Bismarck Thicketbird being listed as a Vulnerable in the 2008 redlist.