The yellow-vented birds in Vietnam could be:
1/ Yellow-vented green pigeon (Treron seimundi),
also known as Seimunds's Pintail Pigeon
2/ Yellow-vented bulbul (Pycnonotus goiavier),
or eastern yellow-vented bulbul,
3/ Yellow-vented warbler (Phylloscopus cantator)
4/ Yellow-vented flowerpecker (Pachyglossa chrysorrhea)
5/ Sooty-headed bulbul (Pycnonotus aurigaster)
Only some individuals have a yellow vent, some have red vent.
6/ Brown-breasted bulbul (Pycnonotus xanthorrhous)
