Before you begin photographing birds in flight, it's important to use the correct camera settings. Once you have applied them, they won't need to be changed, so you can do this before you begin your shoot.
The first camera setting to select is the autofocus mode. I always use the ‘AI Servo’ autofocus mode ('Continuous', on a Nikon camera) when I am photographing birds in flight. In this mode, as the bird flies, the camera will continually adjust the focus, attempting to track the bird's movement for as long as autofocus is activated. This feature isn’t foolproof and doesn't perform flawlessly in all situations but it's easily the best choice for photographing a flying bird.
I usually deactivate all but one of the focus points, leaving only the centre focus point active. Next, I enable all surrounding ‘assist’ focus points. Assist focus points help to retain focus for longer if you're unable to keep the active focus point continually trained on the bird. With previous cameras, I always used the centre focus point for photographing birds in flight. But with the Canon EOS 1D Mark IV, I can usually track birds accurately using any focus point. This allows me to be more creative with my compositions and to focus very precisely when my subject fills the viewfinder. Some nature photographers advocate the use of multi-point focus modes when photographing birds in flight against a plain, high contrast background. Activating all focus points will help if you are trying to grab a flight shot of a small bird from a hide, as it passes by in front of you (e.g. to land on a feeder). In this situation, you will not be able to track the bird, so you need all the focusing help you can get.
Many cameras offer a range of motor drive settings, such as single shot, silent, timed, low speed and high speed. Select high speed (or its nearest equivalent) when photographing birds in flight.
Some cameras also offer a choice of fixed or user-customisable burst speeds during continuous shooting. For photographing birds in flight, set your camera's burst rate to the fastest supported speed.
I always use the Evaluative metering mode when photographing birds in flight. This is similar to the Matrix metering mode on a Nikon camera. Long ago, I decided to learn how to use a single metering mode well in all situations, to allow me to eliminate another variable from my thinking in the field. Now that I understand my camera's metering foibles, I really don't need to use any other metering mode.
Another setting I never change when photographing birds in flight is the exposure mode. I always use Manual (M). On most shoots, the ambient light levels vary far too much to allow me to entrust any of the fully- or semi-automatic exposure modes with the responsibility for managing the exposure. 'Never change'? Every once in a while, I get lazy and try aperture priority (Av) again but I always end up regretting it. Manual exposure mode puts all the control - and the responsibility - on my shoulders. It requires me to check and recheck everything, for every sequence of shots. It's that drilled-in discipline which most boosts my keeper rate. Whenever I use aperture priority, I almost always forget to keep a close eye on my shutter speed and then I pay the price by messing up a shot.