Arial Mating Swifts

Whilst I was in the garden yesterday, looking up at the Swifts I saw something I've not seen before. There were two Swifts in flight together and in a split second one maneuvered itself above the other and they mated. It was all over very quickly. I was amazed, but suspected it would be common. When I mentioned it to Roger today he said that I was lucky to have seen it, so I thought I would look into it a little more. The link below is interesting, with in flight, arial mating shots:-

http://www.commonswift.org/Aerial-mating.html