Place the spout of the funnel inside the neck of one of the balloons. Fill the balloon with birdseed. Press the birdseed down into the balloon to make sure it is filled well. Do not fill the neck of the balloon.
Remove the funnel and cut off the necks of the filled balloon and the unfilled balloon. Cut a few other small holes in the unfilled balloon. Be sure not to cut the holes too large as they will stretch. Stretch the unfilled balloon at the neck and fit it over the filled balloon, positioning the unfilled balloon to cover the neck hole of the filled balloon.