I photographed any of the birds that came close. Afterwards, I found there were swallows and martins (in this case Hirundo rustica) mixed up together. All were exhilarating.
Note the red face and long tail streamers diagnostic of this species.
Canon EF 500mm f/4L IS II USM (handheld).
500mm, f/4, 1/1600, ISO 100.