First I removed the birdfeeder and hollowed out a circle underneath it as wide as the seed was getting spread.  (The rocks come in later.)  The dirt - clay, really - that you see in the middle is what was left after I dug the lawn up.  There were no grass roots in there, so I knew nothing would grow out of it.

If you have birdfeeders, there's a good chance the areas underneath your feeders give you problems.  Even though we use safflower seed without shells, the birds kick or peck so much of it out that we end up with a spongy layer of seed a few inches thick.  The ground-foraging birds like Mourning Doves can't eat the castoff seed fast enough.  So here's what I did to stop it.  Maybe it will work for you.

Stop Birdfeeder Mess

Then I put hard plastic edging around the outside and used spikes to hold it in place.  The edging and spikes should be available at any home-and-garden store.  This keeps our lawn - bermuda grass - from growing into this area.

Next I put landscape fabric over the clay/dirt.  Typically you would use this to stop weeds or grass already in the ground from growing up, but in this case I'm trying to stop falling seeds from reaching the dirt.

I filled the area up with mulch.  I wanted to pile it high enough to hide the black edging, and dense enough to support the rocks in the next step.

I had edged some of our flowerbeds with rocks I bought by the pallet from a local garden center.  What I had left over, or what was too big to put around the flowerbeds, I used in this step.  Over time, the area will look less sloppy as the extra mulch breaks down or washes away, and the grass grows up to the rocks.

Here's what it looked like when I was done.  Now when seed is knocked out of the feeders, the Mourning Doves and other birds have an easier time getting to it because most of it is on top of the rocks.  A few months later I put rock edging around the flowerbed behind these birdfeeders so it all blended together...

Here it is with the rock edging in the background.  When you click on the picture you'll be able to see some green growing up between the rocks.  These are a few safflowers that started growing.  They're not a problem because they're easy to pull -- the landscape fabric and the mulch on top of it don't give the plant anything to really latch on to.  Or you could even let them grow - the flowers are interesting and they don't live very long.

An added benefit to using these rocks is that it provides another habitat for wildlife to use.  The Mourning Doves like to sit on them when it's cold out because the rocks get warm in the sun.    Reptiles and amphibians like skinks and toads can use them for sunning.  Even butterflies can use them for basking or drinking if there's water in a shallow depression on the rock.

I hope this helps or gives you an idea on how to improve your feeder situation.  As I said above, we use safflower seed without the shells, so if you're using seed in the shell, and it's the shells that are causing the problem, I'm not sure if this will help.  It's possible that you would be able to sweep the shells into the grooves between the rocks where they would simply decompose.  Good luck, and thanks for visiting my site.