Here is an excellent Canon EOS R5 review with focus on bird photography. For the Canon EOS R5 Review For Bird Photography a native RF lens and two big white EF telephoto lenses are used.
Jan Wegener reviews the Canon EOS R5 focusing on how well it suits for bird photography. He is tesing the R5 using the RF 100-500mm f/4.5-7.1L IS, and EF 400mm f/2.8L II and EF 600mm f/4L IS II lenses. From the EOS R5 review :
After all the gear reviews lately it was time to head out and do some shooting for myself with my favorite gear. With the Canon EOS R5, RF 100-500 & EF 4/600 L IS II, I headed on the road to find an elusive bird. Rumour has it that he can be found in a small fishing town! Will I find him and my other target species?
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