Ours are still here,we've had a really good year for them with as many as a hundred or so perched on the telephone lines,don't know where they come from as I've not seen a nest round the estate for years but they do seem to like our phone lines.
Ours are still around too. Maybe they've just moved their feeding area. Sometimes ours will seem to disappear for a couple of days, then they reappear.
It'll be swallows perching on your telephone lines paddywak. Swifts never perch. Apart from breeding they spend all their time in the air, even sleeping.