I find a bit odd that a bird with a Western wintering range that is not known to cross any sea on migration arrived throught a ship on a more eastern place.
I also do not understand for the Taiwan bird, why the theory of a shipped assisted bird is advanced rather than a bird just mooved down from their local breeding range in Taiwan.
For the Po Toi one, if it would have been seen on the same time than a Blue-throated Blue Flycatcher or a Chinese Blue Flycatcher, or a Tickell's, that would have been quite strange, but I think it can't be better than be seen together with a Hill Blue Flys, since they share quite similar range. But I fully agree that it can also indicate that the birds have been bought to the same guy who just received an arrival from Indochina somewhere, just before monk release it:-), but I don't believe for this two species that ship-assisted is a good theory, ship-assisted meaning the bird stopped on a ship during migration over the sea because of bad weather and then fly away by themself once they see Po Toi.
But the theory of released birds from the harbour by the customs police after being sceized on a ship from Vietnam or elsewhere in Indochina could make quite sense. All the birds are sold in the bird market should come from somewhere and ship is probably a good options to hide them for this illegal trading.
I think it could be worth to try contact the custom to ask them if they often release birds when they find some during containers inspection.
All the best,
Jonathan
