Thanks.
In my limited experience of this type of photography I think you have to find a way to predict where your subject will be, ready for shooting, for the most successful results.
In my case with these crows when I put food down for them I saw that they would always fly up to a post above where the food was, before either flying away again or flying down to the food. This meant I could just point my camera at the top of the post and click away when a crow either flew to or away from the post.
This was much easier than trying to chase them around with the camera and lens.
Brilliant.
I think I used that method to achieve my first and only good result with this typa shot.
Thank you for the tutoring man