Iambic Trimeter and Iambic Pentameter
The speaker can't quite up his mind about the meter in "To a Waterfowl." He goes back and forth between iambic trimeter and iambic pentameter. Don't worry, Shmoopers. We'll break that down for you right about… now. Iambic trimeter, as you may have guessed, describes a line that has three ("tri") iambs in it, such as line 4: "Thy solitary way." The first and fourth lines of each stanza are written in iambic trimeter, in fact.
So, what about the second and third lines? Those guys are written in iambic pentameter, which means that those lines will contain five iambs ("penta" means five). Here is line 6: "Might mark thy distant flight to do thee wrong." Structurally speaking, this is basically a circle, with the speaker starting out in one place (iambic trimeter), going to another (iambic pentameter), and finally coming back to where he started (iambic trimeter). We'll have more to say about this in just a second, but first we need to tell you all about the rhyme scheme.
Each stanza in this poem rhymes, only it's not the first and fourth lines that rhyme, but the first and third, and the second and fourth, which we diagram as follows: ABAB (were each letter represents that line's end rhyme). The back and forth—from A to B, back to A, and then to B again—mirrors the larger circular structure we've just mentioned (trimeter, followed by two lines of pentameter, and back to trimeter). In both cases, the back and forth, you could say, imitates the flapping of something like… oh, we don't know… maybe a waterfowl's wings. It is a way of performing what is being described: a bird flying around.
With us so far? Great—there's just one more little detail that we need to discuss, and it is of immense, gigantic, super-enormous importance. When it comes to meter, the first and last lines of each stanza are linked (remember, those are the trimeter lines), as are the two middle lines (those are the pentameter lies). If we were talking about a sandwich, you might say that the first and last lines are the bread, and that the two middle lines are the meat and cheese (believe it or not, there's actually a technical term for this sandwich-like structure that you can read about here). When it comes to rhyme, however, the first and third lines are linked, and the second and fourth.
You could summarize this by simply saying every line is related to every other line, depending on your frame of reference. Every line of trimeter (remember, that is the first and last line of each stanza) is also related to one line of pentameter (the second and third lines) via the rhyme scheme. Structurally, the poem is woven tightly together through repeated patterns of both rhyme and meter. The interlocking pieces of this jumbled little puzzle are part of the speaker's main theme in the poem: the order of the universe.
Like the waterfowl—which seems to by flying around randomly but is in fact following a pattern established and maintained by some omnipotent "Power"—so too are the different, seemingly-unrelated pieces of the poem linked. The different lines (those in trimeter, let's say), actually turn out to be related to the pentameter lines via rhyme, even though metrically they're different. There is a purpose to the poem's structure, after all, one that at first might be hidden. It seems like—on the level of form—this poem is actually showcasing same kind of realization that our speaker experiences. Do your minds feel as blown as his right about now?