Killdeer Foraging

Dale and I observed an interesting killdeer behavior three days ago.  Two killdeer were walking in very, very short grass.  The killdeer vibrated the vegetation for a moment, then would take a step and vibrate with the other foot.  Frequently they reached down for a tidbit of food.  The ground was cold and so insects and such wouldn't be very active.  I suspect they were spooking the insects into just enough movement to find them.  I've seen a similar behavior in shallow water done by Bonaparte's gulls, but never by killdeer.  ...... my birds look a little plump, I think partly because they were a little fluffed to keep warm, but mostly because field sketches sometimes turn out a little wonky.