Later to the party...

To the OP - re read Post #17; then do it.

Additionally consider the selection of the AF Operation. On the 90D You have a choice of three.

For a shot like the one in your opening post, where the bird is moving, I would use AI Servo AF. You need to keep the (one) selected AF point on the bird.

There might be suggestions, or you might be tempted, to use AI Focus AF. I suggest you do not use that mode. My reasoning to not use that mode is - for most Photographers I would bet a Mars Bar they'd be using Continuous Shooting: for a novice Continuous Shooting usually plays havoc when combined with AI Focus AF.

WW