Lead poisoning
A condition mainly found in wildfowl which have been feeding in areas contaminated with lead pellets. This can result from shooting or from fishermen discarding the weights from their lines, and the birds may swallow the pieces of lead either accidentally with their food or deliberately in mistake for grit. Mute Swans Cygnus olor are frequent victims on heavily-fished rivers.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver