Red-breasted Nuthatch "vibratory" song

Red-breasted Nuthatches are reported to have three song types, made up of notes similar to the common nasal call notes (see Nuthatch,creeper, kinglet and gnatcatcher calls) but strung together in regular sequences: slow (courtship), fast (agonistic), and an even faster third type known as the vibratory (or copulation) song.
The vibratory song is usually heard near the nest-site, but in this case it was a bird in migration (Mar, PA).