The Common Tailorbird can be best distinguished from the Dark-necked Tailorbird by the presence of a white vent instead of a yellow vent.

1st & 2nd photo: Ben Tre area, Mekong Delta, Vietnam, 22 December 2023
3rd, 4th & 5th photo: Tam Coc, Ninh Binh, Vietnam, 11 January 2024