This is a very productive and fun challenge to improve your ability to draw all kinds of birds, but can apply to anything really. Get 7 pictures of birds that you find interesting, and give yourself 2 minutes to sketch them. Start with the basic forms, shapes and proportions, and add whatever detail you are most curious about with the remaining time. In 15 minutes, you'll have 7 birds sketched which if done daily will help you internalise their proportions. Sketching fast helps remove the worry of being perfect and teaches you what parts of the bird are most important which will be very helpful when drawing in the field.