Recent warmth has enabled the Swifts to feed on the abundance of flying insects, which gives them plenty of energy. Their flying in such conditions is spectacular, with screaming flocks passing the eaves at high speed throughout the daylight hours, literally starting at 4.30am and finishing at 10pm. Most of these screaming Swifts are non breeding birds who are looking for nest sites and in some cases joining existing colonies. We don’t know why they scream in tight flocks, it could be a social activity which bonds the colony or perhaps some form of courtship, we can only guess.
Recently these non breeders have been turning their attention towards the martin nests, hurling themselves at the mud structures to look in the entrances. The martins stay in their nests and defend them. Sometimes they even chase the Swifts in the air. It is unlikely that the Swifts would use the martin nests though this has occasionally been recorded. The martins added additional mud to their nest entrances and made the nests even stronger. Three out of the four pairs on the front of our house did this at the same time as a response to the increase in Swift activity. The slightly heavier Swifts were knocking small amounts of mud from the structures, mainly through the speed at which they landed.
We now have another pair of Swifts in residence. They have taken to a Swift nest box and visit frequently. They will probably build a nest during the rest of their stay and return to breed next May.
Jonathan Pomroy 
I really like that first shot of the swift flying past. I was getting dizzy watching swifts and swallows in the park this morning, I didn’t think it would be possible to capture a shot in flight. I wouldn’t mind watching the martins fortifying their nests!