The speaker of the poem looks up and sees a windhover (another name for the common kestrel, which is a kind of falcon). Windhovers have the ability to hover in place in the air while they scan the ground for prey. The speaker watches the windhover ride the wind like it's a horse, and then wheel around in an arc like a skater, then hover some more. The beauty and power of the bird totally blow his mind, and he's got the exclamation marks to prove it.