I don't really know the history; just was curious and will be presenting some of my google findings here.
First, I came across Rook (chess) heraldry on Wikipedia:
Chess rooks frequently occur as heraldic charges. Heraldic rooks are
usually shown as they looked in medieval chess-sets, with the usual
battlements replaced by two outward-curving horns. They occur in arms
from around the 13th century onwards.
And had this notable image showing the two horns:
NinjaKid (Ollie Martin), CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons
Second, I came across this page on chess pieces in heraldry
Of the six types of pieces used in the game of chess, five are found
in Society heraldry: the chess rook, the chess knight, the chess
king, the chess bishop, and the chess pawn. Of these, only the chess
rook and chess knight have been found in period armory. They are thus
the only pieces which, having a standardized form, can be assured to
have heraldic difference from the others.
The chess rook was common in medieval heraldry, found as early as
c.1285 in the arms of FitzSimon [ANA2 234]; it was a frequent source
of cants, as with Rockwood (Rokewode, Rookwood), 1371 [DBA2 260]. The
chess knight was most frequent in German heraldry, as in the arms of
zu Tratzperg, mid-16th C [NW 69], or of von Hertzheim, 1605
[Siebmacher 95]. The chess knight has two heads by default.
There are some images there I don't know if I can reproduce here, but one is of a rook and is similar to what is shown above. The second image for the knight depicts it with two horse heads.
I was curious about the coat of arms, and while searching, I found this Wikipedia page on the municipality of Pforzen (German). It happens to have the following coat of arms:
The following is Google translated from that page about the coat of arms:
Justification for the coat of arms: The double knight is taken from
the coat of arms of the lords of Pforzen, who were already mentioned
in the 12th century and whose possession came to the Irsee monastery
after they died out in the 14th century. The arrow as an attribute of
St. Point out Sebastian. Another aristocratic family, the Leinauers,
mentioned since the 12th century, was included in the lower part of
the municipal coat of arms. They had their headquarters in the town of
Leinau in the municipal area and had a striding stag in their coat of
arms.
Interestingly, a link in that paragraph leads to the German Wikipedia page for the Rook (Roch heraldry), not the knight. Some interesting quotes (Google translated):
The name can be found in the expression castling in chess. The roc was
the strongest piece in medieval chess (the forerunner of the later
queen had only a few moves). This explains the popularity of the Roch
motif.
As a common figure in heraldry , Roch can be found on coats of arms ,
as it has been in English heraldry since the 13th century. In Rochlitz
in particular , it was already used as a talking coat of arms during
the Saxon rule of Roch. The city has two half roches in its coat of
arms, the nobility had a full roche. The half roches were also known
as hallmarks and guild seals since the 16th century. The French
Roquette family and the Spanish Roquesens family also used the tower
in this way. The game piece rook from chess is shown, whose upper
sides are bent like flowers to the left and right into the coat of
arms field. All colors are possible, but the orientation is based on
black and white towers on the corresponding color surfaces, with gold
being no exception. The resemblance to the lily often led to
confusion. In the coat of arms of the von Rochow family from the Mark
Brandenburg , the Roch mutated due to incorrect descriptionto lilies
or to two horses' heads turned away.
Notice the last sentence, which seems to imply the two-headed horse, at least in this one coat of arms, may have actually been intended to represent the rook, not the knight.
I'm just scratching the surface, and I think there's a lot more to this that's worth exploring. But the commonness of the two-horned rook and its popularity in heraldry, and the way it's at least sometimes depicted as a horse with two heads, makes an interesting case for your two-headed duck potentially having a historical connection to the rook.
