Just wanted to share a link...
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My backyard is NWF backyard habitat certified. It's a great program and I encourage you all to pursue it. It essentially tries to make you a good steward of the earth's resources.
As for the one who expressed concern about attracting squirrels. You don't have to garden to attract them. In fact, part of the program relies on helping you learn to minimize their damage.
I don't think I am mobile enough to do that but just had to mention one bit of wild life I saw in back yard.