What can you do to catch the seed hulls from birds at the birdfeeder?

That's a tough one since birds are quite messy. You might want to use one of the playground rubber type mulch pieces that you can pchase to wrap around the bases of trees. Wrap those around the base of the bird feeder and you can then either sweep or shake them out once the seed hulls are left behind.

Kaytee makes a no waste bird food that work well but is more expensive.

Depends on the type of bird feeder. The first thought that came to mind was glue an old mesh cooking cover to the bottom of the feeder (larger then the bird feeder it's self. You would have to cut the handle off of the cover but most are made from a soft metal so it shouldn't be too hard!

Wild Birds Unlimited also has a net, you hang under the feeder to catch the scraps they drop, then they eat from the net also.

Maybe make a cloth or plastic seed catcher to hang from the bottom.....like what is used on a bird cage in the house

Thanks to each of you for the suggestions. I will try a couple of them.