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The cut with the flock of birds seems to be a re-used scene from Hokuto No Ken #56, which can be found in this post.
https://www.sakugabooru.com/post/show/33681
It seems that these cuts(the flock of birds) was originally a scene of Toei's animated feature film in the 1950s~1970s.

Reference: https://twitter.com/animesama/status/3833170691
>挿入される白鳥は、東映長編の使い回しっぽい。
The first cut it's probably Sasakado those effect are similar to his output in episode 58