There are three things to catch in your first fast sketch. The posture, proportions, and angles. Start with the simple shapes first and build from there. In a circling hawk you may be able to build a compound picture from several different views. If you only get a quick look, do the best you can. I can only hold an image in my memory for a few seconds before needing to refresh with the real bird. You may get an angle of a wing, proportions of a tail or some other detail. You do not have to draw the whole bird if you do not remember what you saw. Drawing hawks in flight is a great way to train yourself to look more carefully at the birds you see.
Click on the first image to start the step by step slide show.