White-throated Swifts Mating in Mid-air

The swifts are back and nesting in California's Central Valley. My son Ben and I were trying to capture good in-flight shots (not an easy task, by the way!) and noticed that they were regularly chasing each other, all the while being very vocal. At first we thought they were males fighting each other, until I got this shot - it sure looks like mating! I apologize for the lack of sharpness - it is a fairly large crop and it was all happening at very high speeds. Has anyone else observed this behavior?

Thanks for posting this Peter. They are certainly amazing birds in many ways!