**Partial answer**

As pointed out by Duck, there is

>! an acrostic yielding ALABIO, our first hidden duck breed.

Now let's turn to the individual lines.

    After the last one, let's start a new canvas; back to the solving, we all need some practice.

>! Hidden duck type: CANVASBACK.

    Less erratic the challenge, but words you must spot; tedious, frivolous, dumbfounded plot.

>! Hidden duck type: (Australian?) SPOTTED.

    Approaching the end, but head to the west; Indians have hints, at puzzles, the best.

>! Hidden duck type: WEST INDIAN (whistling).

    Black belly, white face, solve this with grace; prefix to scar, the suffix bled in a race.

>! Hidden duck types: BLACK BELLIED (whistling), WHITE FACED (whistling). Looks like this is where the embedded Riley is, but I don't have a solution yet.

    I'm a bird, yet a train, used in war, just the same; a lot to find here, autopsy my game.

>! A duck is a bird. There is a train called Duck in the "Thomas the Tank Engine" series. [EDITED to add:] Apparently that isn't the poster's intent, so here's another: the [DB Class 403](https://en.wikipedia.org/wiki/DB_Class_403) train, also known as "Donald Duck". The thing used in war is probably a DUKW. The autopsy might be the abbreviation DUC for "death by unnatural causes".

    Out for a zero, just ditch the bat; dear, there is nothing, left in my hat.

>! When a (cricket) batsman is dismissed without making any runs he is said to be out "for a duck". (I think this derives from the use of "duck egg" to mean zero, because of the shape.) "Duck", like "dear", is an affectionate term of address in some places. My guess is that "nothing left in my hat" is just referring to those duck eggs again, but I could be wrong.

Hints:

>! Eight words, six references: if exactly one of "white-faced" and "black-bellied" is considered a single word, then we have six hidden duck-types and eight words naming them. Or perhaps the references are things like Duck the train, "duck" the term of endearment, etc., but while I don't have more than six of those so far (bird, train, DUKW, zero runs, "dear") it feels as if there should be more than one more. Obviously the fowl is a goose. Er, no, I mean a duck. I'm annoyed at not yet having solved the Riley.