1. For each cake, cut a 12- or 18-in. length of twine, string or ribbon. Loop and tie the ends in a knot. Set aside.
  2. Mix 1/2 oz. gelatin (2 packages of Knox) with 1/2 cup boiling water. Stir well to dissolve gelatin completely.
  3. Add about 1-1/2 cups birdseed to gelatin solution. Mix well. If mixture is still watery, add more birdseed until it has a stiff but sticky consistency.
  4. Line countertop or baking sheet with waxed paper. Place cookie -cutters an inch apart on paper.
  5. Fill each cookie cutter half-full of birdseed mixture. Place knotted end of hanging loop on top center of -mixture. Fill cookie cutter with more birdseed mixture on top of loop. Firmly press mixture with back of spoon to compact in place.
  6. After a few hours, gently unmold each cake onto fresh waxed paper. Let dry, flipping periodically, for 72 hours or until completely hardened before hanging.