Today I found on Spotify:

THE LOUDENBOOMER BIRD sung by Max Bygraves on "Unbeatable Bygraves" (2010)

LOUDENBOOMER BIRD sung by The Four Lads on "The Four Lads Legacy" (2013)

Both of the above stick pretty close to the lyrics already posted—except that the background singers don't seem to be trying to sound like they're German or have German accents. Then there's this:

SPATZENHAUSEN – KATZENHAUSEN – THE LOUDENBOOMER BIRD sung by Eve Boswell on "Eve Boswell International Vol. 1" (2007) – which is entirely in German, or possibly Afrikaans—I'm not sure I could tell the difference. The words are entirely different from "kleine kleine fliegel-flugel" etc. I'm not even sure it's about a bird.

Eve Boswell, by the way, was NOT, as I first assumed, a member of the Boswell Sisters; she was apparently unrelated to them. She was born in Hungary, lived in the UK for a while, and died in South Africa. Some of her songs were definitely in Afrikaans, some in English, some in French—that's all I've been able to verify.

Is it a coincidence that our last guest is from Cape Town?