New answers tagged wildlife
The 50-500 is a really great lens, very sharp. It also has HSM so the focusing speed is good. Beware that it's kind of large. You may be able to rent one from Lensrentals.com to try it out. The 70-200 is not a bad idea as you can get those really sharp, but a 2x TC drops light and may interfere with auto-focus.
Please also consider a Canon 400mm/F5.6. It does not have IS, but is a great lens for birding. Please take a look at the pictures of Lynn David Cole on Google+ https://plus.google.com/u/0/photos/114059849407766199667/albums/5798092835539172337 and view them in Full Screen/Slideshare mode. Almost all of these shots are made with the above lens.
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