I only have a budgie, but I assume all birds would like burls because of how easy they are to shred. Just go out in the woods, preferably with a small handheld saw for thicker branches, and cut burls off of pine trees. Bake them in a oven at 200 degrees for 10 minutes and let them cool, then the birds can have them. My budgie pulls off all the bark within a few days, so be sure to get several. A good size tends to be 2-3 inches long. plus they're free!