AF-C / auto / and in the menu A3 to "quick" and "erratic".
I normally don't use the "auto" AF setting, but in this very challenging case with a static background 20-50 cm behind the very fast and erratic flying swallows, and after taking +500 pictures, it worked the best.
As a matter of fact not just "it worked the best", but significantkly better than all other possible AF settings.
With this setting, the keepers rate number where a swallow was in focus reached over 70 % of the images.

Further more, for all my BIF pictures I use for the A1 AF setting "release+ focus"; "Release + focus" gives me a very significant higher number of keepers than "focus + release".


Update: Underneath some recent images with AF-C set to "release + focus"
Click on the image to open the link.


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Sincerely.
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