I think I have experienced almost everything you guys mentioned here! camera settings, tripod, environmental variables......,most important, the photographer our-self, is the main fact that effect our keeper rate. like Joel said, I'll be very happy if I can get 1 or 2 great shots every time out shooting.
one thing I want to add (Joel actually mentioned) is that learn when not to take pictures if condition lighting are not right.
there are a lot of time you want to kick your self for missing a great shot, but on the other hand, if it's so easy to get great shots, I'll be tired of it pretty soon. that's one reason I think taking pictures of birds has so much fun!
it's a great feeling of knowing that I'm not alone[] , thanks guys for your inputs