The Tutorials on this website are now a mystery to me - there were dozens of them when it was PhotoRadar. However, keep your eyes open on the Home page - there are links to new tutorials, reviews, news and other stuff all the time - and
this one about photographing birds in flight was on there a few days ago (and is still there if you scroll down).
I haven't read it, but I guess it would recommend:
a fast lens
get as close as you can
practice panning
tripod or monopod if possible.