Cut the bottom out of a used metal coffee can using a can opener. The metal cans work better than plastic ones because they are uniform in size on both ends and the lid will fit on both ends.
Cut the plastic lid of the coffee can in half using scissors.
Place one half of the lid on each end of the can, making sure you have them lined up uniformly.
Tape the lid halves to the coffee can using duct tape.
Punch or drill a hole in the roof of the coffee can on each end, near each edge. You will have two holes, almost directly above the taped lid halves.
String a piece of rope or wire through the holes and tie it around a tree branch, with the coffee can hanging below.
Fill the can with birdseed, making sure that you have the can level so it doesn't slide to one side, causing birdseed to fall out.