LEAD TOXICITY: CONSEQUENCES AND INTERVENTIONS 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 microg/g, 0.5 microg/dl, and 72.48 +/- 21.83 microg/g, respectively. The whole-blood lead concentrations were 56.58 +/- 11 microg/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 Ca2+EDTA and the topsoil inside the enclosure was replaced. As a result, the lead concentration in the enclosure soil dropped to 14.74 +/- 14.39 microg/g, and the whole-blood lead concentrations declined to 42.75 +/- 11.64 microg/dl. It was concluded that lead concentrations in whole blood in excess of 100 microg/dl leads to clinical signs of lead toxicity in the CGV. Lower levels appear to interfere mainly with reproductive potential.

Blood lead concentrations in free-ranging Nile crocodiles (Crocodylus niloticus) from South Africa

“…After humans, most of the literature that addresses Pb as a metabolic poison focuses on Aves. The link between birds spanning a wide-variety of taxa and the ingestion of Pb is well documented (Fisher et al 2006;Lambertucci et al 2011;Naidoo et al 2012;and references therein). Recent research has established clinical concentration levels in bird populations due to the direct and indirect ingestion of Pb shot and fishing tackle, which has prompted several countries to ban recreationally-used Pbbased bullets and sinkers (Thomas 1997).…”

Lead Exposure in the Critically Endangered Bearded Vulture (Gypaetus barbatus) Population in Southern Africa

“…Vultures dissolve and absorb lead soon after ingestion due to their low stomach pH, often resulting in acute death (García-Fernández et al 2005, Fisher et al 2006. Sublethal or chronic exposure (prolonged exposure at lower concentrations) is also of concern because it can make birds less fit and predispose them to other causes of death (Mateo et al 2003, Pain et al 2007, Berny et al 2015 or may affect reproductive success (Buerger et al 1986, Gil-Sánchez et al 2018, behavior (Scheuhammer 1987), or physiology (Burger 1995, Fair and Ricklefs 2002, Naidoo et al 2012.…”

Lead ingestion as a potential contributing factor to the decline in vulture populations in southern Africa

“…The closest indication of toxicity was described by Naidoo et al (2012) in a captive Cape Griffon vultures (G. coprotheres) breeding colony, exposed to high lead concentrations within their enclosures at the South African National Zoological Gardens in Pretoria. In this case-study, they described signs of decreased egg hatchability, embryonic death and abnormal chick development concurrent with whole blood lead concentrations ranging between 50 to 100 μg/dL in the adult birds.…”