Thanks for the comments everyone, birds in flight can be a tricky subject and a lot of luck is required.
David - for most of my BIF photos, I use the Canon 400mm F5.6L on either a 40D or 7D. I generally shoot at 1/1600 sec, F5.6 and ISO400 although I may change this up or down by 1 to 1 ˝ stops depending on time of day, background and the direction of the light.
Cheers
Dennis