Swifts have flown the nest

The swifts nesting next door have left the nest. First thing in the morning they scream around the houses, performing their normal low level flight and acrobatic skills 

My best guess has been 15 in the flock. I have guessed there to be 4 pairs nesting because of there being 8 swifts that have flown together since then. My wife said she saw swifts flying into the eaves in a house down the road, so maybe they join up before flying off to feed. I have only definately seen 3 pairs enter the eaves nest door, but they are very quick and it would be easy to miss it.

Swifts fly late into the evening, after sunset