The frequency distribution of lead concentration in feathers, blood, bone, kidney and liver of golden eagles Aquila chrysaetos: insights into the modes of uptake

Abstract

Several cases of acute lead poisoning of golden eagles Aquila chrysaetos have been documented in the Alps. The question, however, remains how often golden eagles take up lead (once, chronically or episodically) and whether this uptake is in fatal or sublethal amounts. We approached this question by examining the level and frequency distribution of lead concentration in different tissues and in three segments of flight feathers in 41 golden eagles found dead, injured or moribund in the Swiss Alps. The frequency distribution of lead concentration in the blood, liver, kidney, wing coverts and shaft of flight feathers were all right-skewed. The highest values in blood, kidney and liver reached levels typical for acute fatal poisoning. In contrast, the frequency distribution of lead in bones was more symmetrical, but 71 % had bone lead concentrations >10 µg/g, which are considered elevated, and 29 % >20 µg/g, values often observed in cases of lethal poisoning. In 22 % of individuals, only one segment of a flight feather had a high lead concentration, while the other two segments had a low concentration. These findings indicate an episodic intake of lead of various amounts that may be immediately fatal (generating high blood levels) or sublethal. The patterns of lead in flight feathers and in bone suggest a repeated sublethal lead intake by the same individual. Such an episodic lead uptake seems only possible through ingestion of lead particles from carcasses or offal left behind by hunters. This also constitutes a risk to other scavengers, notably to the bearded vulture Gypaetus barbatus for which several high bone lead values have been found.