Known from the Mekong basin (Ref. 30857, 4792, 43281). Found in Ban Hang Khone at Don Khone, 3 km below the fall line of the great waterfalls of the Mekong basin at Lee Pee (Ref. 9497). Previously very common in the January-February migration at Ban Hang Khone, but it is now uncommon and may be more reduced than most species (Ref. 12369). Museum: Mekong at Ban Hang Khone, just below the Khone Falls, CAS 94272 (Ref. 5515). Becoming locally rare (Ref. 43281). Also Ref. 7050, 37767.