Doug Brown and Arash Hazeghi are two of the most skilled bird photographers with a special focus on birds in flight.
They both recently published reviews of the new Canon EF 4/600L IS II which looks like the best lens for bird photography Canon has ever made. Incredibly sharp and with a weight of only ca. 3.9kg – which is about 27% lighter than the old version about about the weight of my Canon EF 4/500L IS (the new EF 4/500L IS II is about 3.2 kg).
Too see there reviews click on the following two links: