I'm on board a ship in the South Atlantic. We originated in Buenos Aires and we discovered after sailing that we had several uninvited avian guests on board, including a Vermillion Flycatcher!
Here is one of the birds we had, and which I cannot ID using de la Peņa and Rumboll's Birds of Southern South America and Antarctica.
I'm assuming the bird is a finch but cannot go any further with the ID.
You really can't do anything about it Axel. Ship-assisted movement of birds is a very common phenomenon well-known to bird watchers. We had at least 7 birds of 5 species on board, which is the most I have ever seen (I usually see one or none on the cruises I am on). The birds were feeding on board on moths and other insects and seemed healthy, (and un-catchable if that's what you had in mind). I'm afraid you just have to let nature take its course in these situations.