Remember all those figure sketches you had to do in 30 seconds in life drawing class? Didn’t they seem like a waste of time, because after all, what can you really draw in 30 seconds? Many years later, I am finding quick, gestural drawing to be an excellent way of really understanding how subjects move. By working quickly, you are forced to grab the purest essence of what makes a bird a bird–how it balances on a branch, how its feathers puff out against the cold, how it looks as it takes off with its wings fully spread.
Drawing in this manner is appropriate for any subject that you wish to depict in motion–cars, figures, animals–anything that moves! I find the best media for this to be ones that are the most immediate, charcoal and watercolor work very well because you can block in large areas with form and value. Throw a little bit of line work on top with a Sharpie, and you are able to really capture the movement quickly and efficiently.
Try not to focus on the outcome when you do this–rather, try to learn something about the subject you are studying. That’s why it’s called studying, because you are doing it with the intent of learning, not of creating something that is a masterpiece.