We are entering the murky waters of Khao Lak in Thailand and the even murkier ones of heron taxonomy. This is a member of the Ardeola species, but apparently it is almost impossible to distuguish Ardeola speciosa (Javan pond heron) from Ardeola bacchus (Chinese pond heron) outside the breeding season. Their non-breeding ranges overlap, so take your pick.
The species Anastomus oscitans ranges from the Indian subcontinent all the way to Thailand. I saw this one on the hunt in Ayuttaya a few years ago.