I read this about 3-4 years ago, I think, in the 2015-2018 timeframe, as the first story in a collection, in English. I don't remember what the other stories were about. I forget exactly how the researcher comes to this information, maybe through an old photograph where he spots the dodo in the background, long after when they were considered extinct, but there's a farm which has a flock of "ugly chickens" which apparently were the result of an ancestor receiving a few dodos that they've been breeding. By the time he gets the evidence, I think that group of dodos are all dead, although he finds their bones, which prove that they survived for some time. I think he does locate one last living dodo (I think it might have been a spinster, who was difficult to track down because she'd changed her name), but of course, it's not enough to actually save the bird. Nonetheless, he feels satisfied for having chased this dodo down this far.
He might have been a journalist rather than a researcher. I have vague memories of him wiring for money to continue his pursuit, with the prize being either the proof of the dodo's survival for research, or for a news story. I think there was also a bit of narrative going on with the family with the dodos seeing them as a sign of their misfortune, maybe resulting in their demise when they're poisoned or otherwise killed to get the figurative albatross off their necks.