Thank you for all of your comments! I think, they are a perfect remedy for painful back bones!
As mentioned, all pictures have been taken with the 7DII and the 100-400 II. Most of them at less than 200 mm - otherwise you really can't catch them in full flight. Just tried it with 300 or 400 mm - I did not even get them into the viewer - no chance at all!
I was very lucky that day. It was raining in the morning, the insects flew very low - some just passed within less than 10 feet in front of me (I was never that close to swallows before). I first had to try to catch them in rainy conditions. No chance. After the rain stopped, I succeeded to get the first sharp images. But only with the first sun rays, the pictures became better. The insects (and therefore the swallows) flew higher within quite a short time, which meant no more pictures of swallows.
To Jack Douglas: I add two of those pictures again - this time uncropped.