Hi JoAnn,
I'm guessing that the Killdeer are here because of the previously warm
weather which may have drawn them here a bit early. I've heard lots of
stories from other wildlife rehabbers about summer birds already being
here.
Regarding their feeding, since their diet consist almost entirely of
insects they might not be eating the bird seed for that reason.
Apparently about 2% of their diet does consist of weed seeds and grains,
however, so it doesn't hurt to try. Maybe you can toss them a bit of
millet and see if they eventually show an interest. They feed in wet
areas, looking for insects so you might sometimes see them in a puddle,
as I did while driving down Dorset St.
Ellen Jareckie
Shelburne, VT.