I have never really looked at topics such as this on MacRumours before. There are some great photos here. I bought a Sony A7RV about 18 months ago with, among other lenses, a Tamron 50-400. Now this is probably right down the lower end of focal length for taking bird photos but with 61MP there is room for cropping. And if you can get relatively close to the birds it's fine. Anyway, I have been doing a little bit of bird photography. This is one of the first photos I took with the camera. It is a Rainbow Lorikeet on a grape vine growing on a fence in my backyard.
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I'm looking forward to posting more bird photos on here in the future.