The White Ibis is a strange looking bird with its long red curved bill. I rarely see them flying as they always seem to be head-down, looking for food in the shallows of a lake or bayou.
Some folks have reported auto focus issues with the EOS 40D and 50D in AIServo mode. I’ve never noticed this with either camera and in fact, the 50D’s AF system seems very accurate and fast for me. In my opinion, there’s no better real-world AF test than capturing birds in flight and if you want to check focus look right at the bird’s eye.