Swifts first heard over Exeter on Thursday 5 May evening last week.
My relative pitch, or instrument tuning, or quite possibly both, may well be off, but the calls seem to be in the region of G# and E, though the note also seems to modulate microtonally mid-call. Groups congregate in 'screaming parties' as they zoom around their nesting areas. The female calls are at higher pitch.
Click here for a link to the British Library sound archive recording of swifts, and here for a more in depth analysis of the calls.
There's that well-quoted poem by Ted Hughes. Which I'm not going to quote. But here is a link to the lovely guitar piece 'Birds Flew Over the Spire' from Gary Ryan's 'City Scenes'. It's meant to be about swallows, but for a city scene, I'm thinking swifts, circling high above St Michael's church on St David's Hill (it's in E major, so both E and G# feature ...)
Some more swift info:
Swift conservation www.swift-conservation.org/