Photographing a bird soaring in the sky captures an important part of its essence, particularly birds like the Magnificent Frigatebird that spend much of their time on the wing. Although a soaring bird is in motion you may be able to track the bird through your viewfinder so you are ready to take your shot when the moment is right, or take several shots to choose from later.
When is the moment right? Usually you will want the bird to be close enough to capture details. Depending on the situation, you may have the option of photographing the bird coming at you, right above you, passing by you or leaving you, each of which makes a different impression and all of which can be useful. You may also want to time your shot so blue sky is behind the bird. It can be very difficult to get the right exposure if clouds or the sun are in the background, although sometimes clouds or other backgrounds can be interesting.
Here are a few examples to consider: