Take a Survey Rholands Hall 07 Nov 2019 Oral Presentations | Moderated Discussion
Parallel A - Rholands Hall 14:00 - 15:30

Lead (Pb) is a heavy metal that is increasingly being demonstrated to be harmful to wildlife and humans. While this issue has received significant attention in Europe, North America and other parts of the world, it has received relatively little attention in Africa. Recent studies on vultures, crocodiles and mammals in southern Africa have recorded high levels of lead, and bullets, fishing sinkers and mine pollution have been implicated, but a full analysis of sources of lead has not been conducted, nor has the impact of lead at a population level or in other groups of organisms been assessed.

The purpose of this interactive session is to:

  • Provide an overview of physiological processes and impacts of lead in wildlife
  • Present a global overview of lead sources and issues related to lead in wildlife, people and the environment, including an assessment of efforts to reduce exposure of wildlife to lead
  • Present the results of recent southern African studies evaluating the presence and impact of lead on wildlife and the environment
  • Discuss a research framework in relation to understanding the sources, impacts and alternatives to lead
  • Discuss a monitoring framework for assessing progress towards ensuring that wildlife is not harmed by exposure to lead
  • Discuss an integrated, multidisciplinary approach towards achieving a vision that South African wildlife is not harmed by exposure to lead.

Delegates are invited to attend the session to become more familiar with the details and issues relating to lead in wildlife, and contribute to interactive discussions towards developing strategies and approaches to ensuring that wildlife is not harmed by exposure to lead.

Blood lead concentrations in free-ranging Nile crocodiles (Crocodylus niloticus) from northeastern KwaZulu-Natal, South Africa Take a Survey
14:00 - 14:15

Generally, crocodilians have received little attention with regard to the effects of lead toxicity despite their trophic status as apex, generalist predators that utilise both aquatic and terrestrial habitats, thereby exposing them to a potentially wide range of environmental contaminants. During July - October 2010, we collected whole blood from 34 sub-adult and adult free-ranging Nile crocodiles (Crocodylus niloticus) from three separate populations in northeastern South Africa in order to analyse their blood lead concentrations (BPb). Concentrations ranged from below detectability ( < 3 μg/dL, n = 8) to 960 μg/dL for an adult male at the Lake St Lucia Estuary. Blood lead concentrations averaged 8.15 μg/dL (SD = 7.47) for females and 98.10 μg/dL (SD = 217.42) for males. Eighteen individuals (53%) had elevated BPbs (≥10 μg/dL). We assessed 12 general linear models using Akaike's Information Criterion (AIC) and found no significant statistical effects among the parameters of sex, crocodile size and population sampled. On average, crocodiles had higher BPbs at Lake St Lucia than at Ndumo Game Reserve or Kosi Bay, which we attribute to lead sinker ingestion during normal gastrolith acquisition. No clinical effects of lead toxicosis were observed in these crocodiles, even though the highest concentration (960 μg/dL) we report represents the most elevated BPb recorded to date for a free-ranging vertebrate. Although we suggest adult Nile crocodiles are likely tolerant of elevated Pb body burdens, experimental studies on other crocodilian species suggest the BPb levels reported here may have harmful or fatal effects to egg development and hatchling health. In light of recent Nile crocodile nesting declines in South Africa, we urge further BPb monitoring and ecotoxicology research on reproductive females and embryos.

Association between hunting and elevated blood lead levels in the critically endangered African white-backed vulture Gyps africanus Take a Survey
14:15 - 14:30

Lead (Pb) toxicity caused by the ingestion of Pb ammunition fragments in carcasses and offal is a threat to scavenging birds across the globe. African vultures are in critical decline, but research on whether Pb exposure is contributing to declines is lacking. In Africa, recreational hunting represents an important economic activity and can support conservation objectives; however, Pb in leftover hunted carcasses and gut piles represents a dangerous food source for vultures. It is therefore important to establish whether recreational hunting is associated with Pb exposure in African vultures. We explored this issue for the critically endangered white-backed vulture (Gyps africanus) in Botswana by examining their blood Pb levels inside and outside of the hunting season, and inside and outside of private hunting areas. From 566 birds captured and tested, 30.2% birds showed elevated Pb levels (10 to < 45 μg/dl) and 2.3% showed subclinical exposure (≥45 μg/dl). Higher blood Pb levels were associated with samples taken inside of the hunting season and from within hunting areas. Additionally, there was a significant interaction between hunting season and areas, with Pb levels declining more steeply between hunting and non-hunting seasons within hunting areas than outside them. Thus, all our results were consistent with the suggestion that elevated Pb levels in this critically endangered African vulture are associated with recreational hunting. Pb is known to be highly toxic to scavenging birds and thus we need to urgently explore ways to reduce exposure to Pb ammunition to help protect this rapidly declining group of birds.

Blood and bone lead levels in South Africa's vulture species Take a Survey
14:30 - 14:45

Lead is a toxic heavy metal that serves no known biological function in any living organism. Its usefulness and malleability as a metal have made it pervasive in many aspects of human society and industry, despite the fact that its harmful effects on human and animal health have been well-documented. As obligate scavengers, vultures are especially susceptible to dietary toxins, including lead poisoning. The insidious nature of lead poisoning could lead to a range of difficult-to-diagnose symptoms in birds, ranging in severity from mild to severe and even fatal. We conducted a nationwide assessment of the levels of lead toxicosis in South Africa's birds in general, and in vultures in particular. Blood and bone lead samples indicate that a significant proportion of white-backed vulture (Gyps africanus) and Cape vulture (G. coprotheres) are displaying elevated lead levels. Non-vulture species, across all tissue types sampled, showed lead levels that are consistent with background exposure, suggesting that certain elements of vulture ecology, such as their scavenging lifestyle, are making them particularly vulnerable to lead poisoning. Of particular concern were the high lead levels found amongst the unfledged chicks of a white-backed vulture breeding colony near Kimberley. Since these chicks are not yet mobile and display degrees of lead poisoning ranging from background to severe, we suggest that these chicks are not merely ingesting lead from diffuse sources such as dust from mining activities, but are also receiving metallic lead particles from carrion fed to them by their parents. Our findings point to fragmented lead ammunition as the probable source of the lead poisoning.

Lead toxicosis in southern ground-hornbill (Bucorvus leadbeateri) in South Africa Take a Survey
14:45 - 15:00

In 2016 an adult southern ground-hornbill (SGH; Bucorvus leadbeateri) presented with acute lead toxicosis due to lead particles in the gizzard, which required chelation treatment. The source of the lead, in this case, was a carcass of a porcupine that had been killed with lead shot. This was the first documented case of lead toxicosis in SGH. Subsequently, a further six wild birds have presented with clinical signs, and five have been successfully treated. Three additional instances in captivity have been documented. Ground-hornbill populations are declining from a myriad of anthropogenic threats, and this, coupled with slow reproductive rates and extensive habitat requirements, has resulted in the uplisting of SGH conservation status to globally Vulnerable and regionally Endangered. Vulnerability to lead toxicosis is now considered a recognised, and preventable, threat to SGH. Their foraging and social behaviours make then vulnerable to lead poisoning from both lead bullet fragments and shotgun pellets. As a result of these incidences, every individual handled as part of the research and monitoring conducted by the Mabula Ground Hornbill Project, is routinely tested in the field for blood-lead using a portable field lead analyser. Any individual with a blood-lead level greater than 10 μg/dL is chelated, as this is the minimum level where clinical signs have been observed. In 13 randomly sampled wild SGH, 12 showed no lead exposure, suggesting no general environmental exposure, but rather infrequent or occasional encounters. Through working with custodians in the SGH range, a movement toward the use of lead-free ammunition and/or safe disposal of carcasses or offal where lead may be present is being promoted. Other potential sources of lead still need to be investigated but in the interim ensuring that SGH are not exposed to lead from bullets from any source should be a priority conservation action.

Towards establishing background lead exposure in South African vultures Take a Survey
15:00 - 15:05

Documenting cases of the elevated exposure of vultures to lead, and making decisions regarding the treatment of exposed birds, requires an understanding of natural baseline blood lead levels. This has not yet been done for vultures in South Africa. To address this gap, blood lead levels of 105 vultures of two species held in captivity have so far been tested, and testing is ongoing. These captive birds are fed a diet free of bullet lead fragments, there is no environmental exposure to possible concentrated sources of lead (e.g. batteries, bullets, sinkers), and there is no lead-containing paint used in the enclosures. Therefore the blood lead levels are reasonably assumed to represent baseline environmental exposure. The results, when obtained, will be used to inform the standard operating procedure for testing and treatment of lead-exposed wildlife.

Tshwane University of Technology
University of Cape Town
BirdLife South Africa
Mabula Ground Hornbill Project
VulPro NPC
Ezemvelo KZN Wildlife

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