You asked
What shutter speed for birds in flight?
For birds in flight, aim for 1/2000s or faster. Most sport needs about 1/1000s, and people running can get by with around 1/500s, but wings move quickly and need the extra speed. Going that fast pushes ISO up, so a body that stays clean at high ISO matters, and modern noise reduction software helps too.
Speed alone won't catch the wing at the right moment. Fast bursts and a deep buffer make a big difference, and subject detection that tracks birds and their eyes is the biggest reason to choose a recent mirrorless body for this work. Read more in Wildlife and sport.
Written by Claude from this site's pages.