I just heard a coment of a professor for history. She is an expert on everyday culture, like food. For an interview she researched about the rumor, of catholic monks eating beaver during the season of fasting. She said, that she found no evidence of monks eating beaver or something elselike. She supposes it was a spreaded rumor in the times, to make fun of them for beeing bigoted or stupid.

The source is an German History-Podcast from the Federal Public Radio DLF. I think, its quit hard to understand it, if your not really fluent in German. In the End, its just an German History Professor talking about one topic. Its kinda sober(?) ivory tower German :| But if you understand it, I can fully recomend it. One of my favorite podcast.

Aus der Dlf App | Der Rest ist Geschichte | Fastenzeit – Mäßigung und Magenknurren …deutschlandradio.de/dlf-audiothek-audio-teilen.h…

Die historischen Wurzeln der Fastenzeit sind rätselhaft - doch Verzichten ist bis heute ein Trend

Die Fastenzeit hat begonnen. Über ihre historischen Wurzeln ist wenig bekannt. Doch Verzichten ist auch heute noch im Trend: von Handyfasten bis Null-Diät.

Deutschlandfunk
Beaver was commonly eaten by Canadian settlers of the period, though, so it’s more “Can we still eat beaver on Fridays” than “We’re going to eat beaver now”
Ah yeah ok. It was only a sidenote in this program. She didnt tell for which region she checked the sources. But all the sources she explained were from Europe or nearby (Byzanz fe)