"Yumbri" is the name used for themselves by small bands of hunter-gatherers in northern Thailand and neighboring Laos. Their population was estimated at about 150 in 1938. Their traditional hunter-gatherer subsistence economy may now have largely disappeared. Yumbri are known to the Lao and Thai as "Phi Tong Luang" and are called "Ma Ku" by the Meo.
Boeles, J. J. (1963). "Second Expedition to the Mrabri ('Khon Pa') of North Thailand." Journal of the Siam Society 51:133-160.
Pookajorn, Surin (1985). "Ethnoarchaeology with the Phi Tong Luang (Mlabrai) : Forest Hunters of Northern Thailand." World Archaeology 17:206-221.
Weaver, Robert W. (1956). "Through Unknown Thailand." Natural History 65:289-295, 336.