Yes, in comparison, humans, jet planes and race cars and much easier to track and keep in focus than a green-winged teal flying close at 40-mph. Speed, plus unpredictable flight patterns and changing backgrounds, all make flying birds really tough. Don't try to hunt for the subject in the viewfinder. Instead, look at the subject as you're raising the viewfinder to your eye. Practice that with perched subjects at first, then start with moving subjects. Gulls, if you have them in your area, are great practice subjects, because they're often plentiful, somewhat fast and erratic in flight pattern.