Vocal Sacs on a Passerine!

I think the presence of vocal sacs – that is, bare patches of skin inflated during singing – should have been plenty of evidence to have placed the Black-capped Donacobius in its own family deacades or centuries ago. But museum ornithologists seemed to be hell-bent upon forcing this obviously unique taxon into already named families. So the donacobius has been called a wren, a thrasher, and who-knows-what. But when you actually experience the bird in the wild, you are quite aware this bird is like no other in the world.

Here, on the floating vegetation of an oxbow of the Rio Cuiabá upriver from Porto Jofre, Mato Grosso, Brazil: