@adrianfry depends on your budget. 2nd hand market or new, but Contemporary' or 'Sport' 150-600 are popular among amateur photographer currently. I must say I haven't used the lens, but have seen many photographs from people who use this lens. Also, I'm not a Canon user, but I do know the best glass costs a fortune. I started with a 70-300 kit lens....I soon found out it wasn't up for the task.
@adrianfry I love my prime, but a few months after I brought it, Nikon brought out a 180 - 600mm. I may have brought that instead. Sometimes, zoom can be handy when panning and for surprise birds that appear to close for my prime.
@adrianfry but the more you try the better you become at anticipating. (I've been photographing birds for just over 2 years and gone from poor to not to bad in that time and have enjoyed the journey).
Some of my sharpest shots are of birds that just appear on fences or branches as I go round a corner. Or a rabbit that is eating on the grass etc... It pays to anticipate.
@adrianfry thanks. I'm not a person who chases the rare and obscure (I do take the odd trip to parts of the country that has birds we don't have) I love the familiar and common. I love going to the the same location over and over and witnessing the changes over the seasons whilst learning when is best for Migratory birds and learning about bird behaviour. It all helps getting closer and better photos.