AI focus is where the camera tries to guess whether One shot or AI Servo is the best focusing type. Unfortunately, cameras are never as good as humans for deciding this and have a tendancy to get things wrong (addition to Murphy's law - when it does decide to go wrong it will do so in the worst possible way.)
My thoughts for Focus type for birding - AI Servo for Birds in flight, One shot for Birds at rest. Thats certainly the best in my experience with motorsport (not done birding but similar high speed objects)
Having a camera makes you no more a photographer than having a hammer and some nails makes you a carpenter - Claude Adams
Keep calm and carry a camera!