Melt the rendered tallow (suet) over low heat.
Once the suet is melted, remove from heat and add the birdseed, mixing thoroughly.
Let the mixture rest while you lay out your cookie cutters.
Place a towel down on your work table. Over the towel, lay a sheet of plastic wrap.
Place cookie cutters on the plastic wrap, and press them down just lightly to help the edges meet the cusioned plastic wrap. (This is what will help keep from losing suet mixture out from under the edges of the cookie cutters.)
Cut a plastic or paper straw into 2" lengths. You're going to place these where you want a hole left in your ornament, for hanging.
Once the birdseed mixture has cooled just enough to start being a bit opaque near the edges, it's the perfect temperature for working with.
Working one ornament at a time, use one hand to vertically place and hold the section of straw where you want the hanging hole in the finished ornament. With the other, use a spoon to fill the ornament with birdseed mixture, being careful to get it into every corner. I find that filling a cookie cutter about 3/4 of the way full works best.
Continue working until all of the birdseed mixture is used. Allow ornaments to fully cool. Once set, they can be transferred to the fridge or freezer to finish hardening before removing from the cookie cutters.
Once ornaments are hard and cool, gently press them out of the cookie cutter, using gentle pressure from the top. Then carefully remove the piece of straw. Use ribbon or twine to make a hanging loop for the ornaments, and then they're ready for the birds!