It would appear, based on measuring lead levels in various species of birds, that some are more tolerant than others. Woodcock, for example--per a study by the University of Wisconsin--often show extremely high lead levels. Yet none of the birds studied had lead pellets in their digestive system. And the researchers could not determine the source of the lead. Given what woodcock eat (worms), it only seems logical that they would ingest lead because the soil in which the worms live contains lead, from a variety of sources.