Over the period 1986-1996, declines of Killdeer were much more widespread. The Christmas Bird Count data show similar results to the Breeding Bird Survey data. The declines are on a more local scale, however. The analysis is made possible by the thousands of observers who contribute data to Christmas Bird Counts and Breeding Bird Surveys. Austin tracked down the source of the call and it turned out to be a European Starling doing a perfect imitation of a Killdeer.
Starlings are remarkable mimics.