Step 1: Gather needed items
2-Mesh or Screen--for bottom of tray, something permeable, but that seed won't fall through
3-1/2" or 3/4" piece of wood the same length of the longest side of the frame you chose
4-L-shaped fastener with screws
5-Long nails or Screws, a hammer, and a drill if you have one
Screw the L-shaped fastener onto the wood plank as pictured, so that it will latch over the lip of the window sill. Screw another one to the other side of the wood plank.
Step 2: Fasten mesh to tray bottom
Step 3: Attach tray to wood plank/fastener
Step 4: Install to window
Add your seed. And hold in place and close the window.
Step 5: If you build it, they will come
Step 6: Invite local birds
You can see the fasteners well in this photo.