It all started with an innocent message.

On October 19, I received a note from good friend Jonathan Newman.

"I wanted to pick your brain about the Rio de Janeiro Antwren and what your opinions are. It’s obviously an enigmatic taxon but there is so little online about its validity even. I read a mist-netting study from REGUA where they caught consistent specimens but they were all luctuosa (Silvery-flanked Antwren) once they were in the hand. What is your opinion and that of the Brazilian top rank birders? Is it a thing? Is it extinct? Is it a plumage morph of luctuosa? I know what I think but maybe I’m biased haha."

I didn’t realize it at the moment, but that message would send me down a small rabbit hole that mixed science, stories, and a pretty strange sense of loss. 

It would lead me into conversations with people like Luciano Lima and Gustavo Bravo, and into one of the Atlantic Forest’s most intriguing mysteries: the case of Myrmotherula fluminensis, the Rio de Janeiro Antwren. 

A bird that never really existed — or maybe still does

The Rio de Janeiro Antwren was described in 1988 by Luiz Gonzaga, based on a single male specimen mist-netted in Magé, a lowland area at the base of Serra dos Órgãos, just 30 kilometers from downtown Rio de Janeiro.

That’s already remarkable. Imagine: one of the most urbanized regions in Brazil, one of the most studied birding zones in South America — and right there, a bird nobody had ever seen before.

And then, nobody saw it again…

The type specimen — that one individual in the drawers of the Goeldi Museum in Belém — is all we have. It was never photographed alive, never recorded singing, never seen in a mixed flock. 

It’s that one specimen stuffed under glass. That's it.

Over the years, many started to doubt whether fluminensis was a real species at all. Some argued it might just be a strange plumage variant of the [Silvery] White-flanked Antwren (Myrmotherula axillaris luctuosa), which is common in the area. Others went further, suggesting it could be a hybrid — maybe between axillaris luctuosa and urosticta, or between axillaris and unicolor.

In 2017, BirdLife International even removed it from the global checklist, listing it as “not recognized.” Just like that — a species born and gone in a few lines of taxonomy.

Luciano Lima strongly disagrees with this decision and supports this as a valid species.

But as it often happens in ornithology, the story didn’t end there.

Read the rest of Caio's article on the Brazil Birding Experts website here: https://www.brazilbirdingexperts.com/post/the-mystery-of-the-rio-de-janeiro-antwren-myrmotherula-fluminensis