Many raptors have strongly contrasting feathers. You can identify them by the bold dark and light patterns from a great distance. This makes them ideal subjects to explore with drawings on toned paper. With paper that is a mid-value gray or brown, you are not limited to simply pushing the darks by adding graphite with your pencil but can also pull the lights, adding highlights or white feathers with a white pencil or white gouache. Click on the illustrations below to enlarge them.
As shown in the illustration below, the key to a successful drawing on toned paper is to use the color of the paper as one of your values. Do not fill up the page with graphite or white pencil but use the mid-value of the paper as a value in your drawing. This is hard to do. Once you find yourself adding the white pencil it is very easy to fill up the whole drawing.
Add dark and mid-values with a graphite pencil. Note that I have not added any graphite on the back. Be sure to leave some areas of the subject untouched paper. You expand your value range by intentioanaly using the color of the paper as a value in your subject. Here the sunlight shines from the left side of the drawing, making the middle of the bird’s back lighter.
You do not need a toned paper sketchbook. You can cut a few pieces of toned paper to fit inside your regular sketchbook, and slip them in the back of the book to be used at your convenience. When you make a sketch on the toned paper, trace the outline of the paper into your sketchbook as a place holder so that you will have room to glue the sheet into the book, maintaining the chronological order of your sketchbook entries.
Give it a try and let me know how toned paper works for you.