The incei subspecies of Asian Paradise-flycatcher, from China, is a quite common passage migrant in East Tonkin. I have been waiting for a long time in Hanoi the Japanese Paradise-flycatcher, considered as scarce in Vietnam. Finally flew into the right patch!
At first glance, I noticed the black hood extending further down onto breast, very different to the migrant incei APF I am used to seeing on passage. At closer range, breast appeared dark grey but without clear demarcation with the black hood. The incei APF show a sharp demarcation, the blackish throat contrasting strongly with the grey breast.
This bird show also clear maroon tone on the mantle and a dull tail - not bright orangey-chestnut as in APF.
Another detail is the black crown lacking metallic gloss, which also points to female Japanese PF.
The clearly bluish bill and orbital indicates an adult.
Due to its similarity to its more abundant female Chinese cousins, I reckoned the female Japanese Paradise-flycatcher may have been overlooked and under-recorded in Vietnam.