Having just been to Madagascar (2nd time), I reckon many parts are severely underbirded / not birded at all:
- Large parts of the West coast;
- everything from Berenty to Lac Tsimanampetsotsa (S of Anakao); That's a stretch of 400K.
- All forest from Andohahela up to... Ranomafana (with occasionally birders going to Andringitra. That's 500K of forest, in length.
- Same actually for all forest North of Ranomafana until the Andasibe area, and all forest North of Mantadia until... Marojejy?
I mean, birders go to Andohahela, Ranomafana, Andasibe-Mantadia, Marojejy, Masoala and Bemenavika, but at each of these sites we're only scratching the surface and each site is 100ths of kms apart from the others. Only dedicated expeditions venture wider and it's only so that e.g. Dusky Tetraka got rediscovered, and there is still ample room for discovering new locations for birds that seem thin (or non-existent) on the ground in certain areas, e.g. Red-tailed Newtonia, Helmet Vanga, Madagascar Serpent-eagle, Yellow-bellied Sunbird Asity,...