The word vögel, in German, means "bird". There's an intereting slang verb in German related to this word. Vögeln is roughly the equivalent of the English word screw as applied to copulation. So in German, if you want to say someone is screwing, you say they are birding, instead, i.e.:

active construction:
Mikael vögelt Gretchen

translation: Mikael is birding Gretchen

passive construction:
Gestern abend ist Gretchen von Mikael vögelt geworden.

translation: Gretchen got birded by Mikael last night.

It is said that this usage of the noun, vögel, in German came about sometime in the Middle Ages, when particularly amorous lords and ladies were referred to as "screwing like birds." Eventually, it shortened into a verb form.