"The Windhover" is packed with alliteration. As with the poem's use of assonance and consonance, alliteration serves one main purpose overall: to make the poem sound beautiful. This beauty, in turn, is a way for the poem to do justice to both the magnificent sight of the windhover soaring through the sky and, even more importantly, to the majesty of God's creation. Furthermore, the vibrant and frequent use of alliteration relates to the way that speaker projects a state of "ecstasy" onto the kestrel. This ecstasy is a kind of religious fervor, felt and perceived by the speaker (rather than the bird). Alliteration thus heightens the sense that this poem is a kind of prayer directly praising God.
The alliteration that begins the poem is immediately arresting and comes in a group of three: "morning morning's minion," "daylight's dauphin," and "dapple-dawn-drawn Falcon." All three examples sound bright and clear, reflecting the clarity of the speaker's experience—that is, the awe felt by the speaker in observing the bird, and the instinctive connection made by the speaker between nature and God.
From "riding" in line 2 to "wimpling wing" at the end of line 4, the alliteration serves more to evoke the way that the kestrel alternately hovers and dives. As with the poem's meter and rhyme, alliteration comes and goes with a kind of rhythm that creates a sense of stasis and motion—exactly the rhythm that the bird observes in the air. In lines 5 to 6, the /s/ alliteration (sibilance) gives the poem a smooth, gliding quality that relates to the comparison of the bird's flight to the heel of an ice skater:
... then off, off forth on swing,
As a skate's heel sweeps smooth
The next main examples fall in lines 9-11:
Brute beauty and valour and act, oh, air, pride, plume, here
Buckle! AND the fire that breaks from thee then, a billion
Times told lovelier, more dangerous, O my chevalier!
As with all the other instances in the poem, the alliteration here still works to maintain the presence of beauty and deliberate design. But here it's also used to evoke a sense of power through hard /b/ and /p/ sounds (highlighted above). These have a kind of toughness that matches with the description of the kestrel's beauty as "brute." This /b/ sound then links with the speaker's statement that Christ is even more "lovelier" and "dangerous" (meaning powerful)—a "billion times" more.
In line 12, "plod" chimes with "plough" to paint a picture of backbreaking farm labor, the closeness of the sounds suggesting repetitiveness. The three hard /g/ sounds in the final line return to the brightness of the opening, suggesting the intensity of the fire that burns inside all of God's creation ("gall," "gash," and "gold-vermilion"). Ending the poem with a color means that this bright sound also leaves the reader with a lasting impression of reddish-gold.