mastering flight photography article on Richard Bedford's website. An interesting read with lots of practical advice from an expert on the subject. Some of his shots must have been phenomenally difficult to obtain. Swallows for example, being small and fast, are incredibly hard to track, yet Richard has a beautiful shot of one swooping low across water.
My own successes have largely been with much larger or slower birds. The king cormorants in the Falklands were particularly enjoyable to photograph. One day I found a group conducting flight operations from a table of rock on the cliffs at Sealion Island. It was a great location in that it enabled me to position myself upwind of and slightly below the landing area. I spent well over an hour in this vantage place tracking the birds coming in and shooting in bursts as they decelerated to land.
Even with slow moving birds and a good zoom I didn't find it easy to always get the best framing. This is one of my favourite shots from the day - it's just a shame I lost the bottom of his foot. Cold fingers did not help either!