Perning in gyres

The big clock in the sky says it's that time again, when turkey vultures form wheels within wheels, riding vortexes in flocks of hundreds, waiting for the right daytime wind to blow them to the Yucatán, or Cuba, or beyond, with one long cool breath.

It's not what Yeats had in mind when he wrote that line, which won't leave my mind, and has me in its spinning grip.