Lead toxicity : consequences and intervensions in an intensively managed (Gyps coprotheres) vulture colony

Abstract

The National Zoological Gardens of South Africa (NZG) is involved in the ex situ conservation of Gyps coprotheres, the Cape Griffon vulture (CGV) and houses 24 birds in a 100-yr-old aviary. Following the death of one vulture with high liver lead concentrations, an investigation was launched to ascertain the source(s) and consequences of lead toxicity in this breeding colony. Whole blood from 24 CGV, paint from the enclosure, water, and soil sampled at various locations within the enclosure were evaluated for their lead concentration, and data were gathered from NZG’s medical records. The lead concentration in the paint, water, and enclosure soil was 5,100 lg/g, 0.5 lg/dl, and 72.48 6 21.83 lg/g, respectively. The whole-blood lead concentrations were 56.58 6 11 lg/dl. The breeding history of six pairs within the contaminated enclosure since 2002 showed 45 eggs laid, of which 44% were infertile and 24% successfully reared. The medical records revealed evidence of osteodystrophy despite adequate nutrition. As intervention measures, six birds were treated with Ca2þEDTA and the topsoil inside the enclosure was replaced. As a result, the lead concentration in the enclosure soil dropped to14.74 6 14.39 lg/g, and the whole-blood lead concentrations declined to 42.75 6 11.64 lg/dl. It was concluded that lead concentrations in whole blood in excess of 100 lg/dl leads to clinical signs of lead toxicity in the CGV. Lower levels appear to interfere mainly with reproductive potential.