Trev, I would have kept the AF-On button depressed throughout the whole sequence, since the bird was large and fairly easy to track and I was not losing focus on the bird. Also, with the advanced AF features of the 7D and 1 series bodies the cameras can be set up to allow you a little time to get back on track, if you lose the bird from your crosshairs, before it will wander off and look for something new to focus on. Cameras below the 7D, like the 40D, 50D, 5D2 and lower do not offer that feature and thus depend on very fast reactions from the photographer to cease AF temporarily if your AF point slips off the bird.
I will vary the AF point configuration used depending on the complexity of the background. The more inviting the background for the AF the narrower I like to constrain the AF. Thus for the sequence, with all those twigs and things, often quite near the bird, I did not want the AF to get accidentally drawn to the background. Shooting against a plainer background, like the sky, I might well use more focus points. However, shooting with a long lens at wide apertures you may find that the DOF is quite shallow, and the camera could focus on the nearest wingtip, for example. leaving the bird's eye and far wing looking soft, so ideally it is best to try to use as few focus points as you can and to aim with precision at the bird's head. That is not something I am very good at, yet, but I keep practicing. I might also add that the more focus points you use the more work the camera has to do to figure out which focus point is the best to choose for focusing. The fewer points you use the less decision making is left to the camera and far less data to process. So, I would use the fewest points necessary to give me reliable results. If I was shooting swifts and swallows against a blue sky, which I've tried several times with limited success, I would use a wide spread of focus points, because the chances of me locking focus and holding it with a single focus point are about nil. Example of using Zone AF with the 7D....
I used spot metering because I shoot with manual exposure. I do not meter while shooting. I meter before shooting (see post #4 for examples of what I meter from). Therefore I get to pick where I aim the spot when setting my exposure. I would not use spot metering for BIF in any autoexposure mode. Far too much room for error there. If I was to use autoexposure, which is rare indeed, I would probably use evaluative metering, not spot or even partial.
Taking a magpie as an example, spot could easily get confused if you were using autoexposure and metering from the magpie - one minute black, the next white, the next blue sky, the next a bit of white cloud, the next green leaves. It sounds like a recipe for disaster. That is why I prefer to set a manual exposure that befits the incident light reaching my subjects. Then my exposure does not get thrown off by all those tricky variables. The meter can do whatever the hell it pleases while I am shooting. I simply ignore it.
