Camera setting question-canon 450D (1 Viewer)

Hi all, I am needing some help. I have my new camera for a week and starting to see that I need some help with settings for my camera. Here is the delima: I take pictures of birds in trees, brush or anywhere they land and many times while out a hawk will be flying over my head or near by tempting me for a flight shot. I use a zoom lens 70-300mm 1:4-5:6 IS which doesn't give me all the zoom I need but is fine for now. What setting in sports mode or manual would be the best for semi still bird shot and a flight shots? I am using AI Servo and rapid shots setting at this point. Also I may take pics in the morning, afternoon, and evening so my available light is different all those times of the day. I am worried about having to change settings instantly for a sudden appearance of a bird. I usually only get a few chances and poof the bird is gone so not much time to adjust camera then get back to bird if still there.

Another problem I am having is getting a super sharp picture at a distance with birds after zooming in, most of the time at the far limit of the zoom.

Any help is appreciated, I only know enough to really mess things up.

I use AI servo just about all the time for birds including perched birds.

AV setting and AI servo for me as well. I've used the 20D and 40D but I'd imagine settings are pretty similar for the 450D.

For birds against the sky I generally add EV compensation of +1 as they're usually darker than the sky behind and use the centre weighted metering and the single central focus square.

Even if you're not getting perfect results straight away think of it as a learning exercise and try to think about the settings you're using. If you get a decent image then on the computer check the exif details to see what camera settings you used for the photo.

As regards white balance I mostly use auto white balance which generally gives decent results apart from late evening sun which can give overly warm colours. It can be corrected at the time of taking the photos but really I wouldn't worry about it until you're fully comfortable with the camera settings for each photo as it can be corrected on the computer in post processing as well.

Thank you both for the suggestions. I'll give it a try and see what happens.
Thanks again!