Migrating vultures succumb to lead.

Mar 04, 2009

Nam D-H and D-P Lee. Abnormal lead exposure in globally threatened Cinereous vultures (Aeypius monachus) wintering in South Korea. Ecotoxicology doi:10.1007/s10646-008-0275-0.

Synopsis by Carys L. Mitchelmore

An increasingly rare species of vulture that migrates from Mongolia to overwintering grounds in South Korea can pick up enough lead along the way to poison and kill them.

Lead poisoning may be the reason a globally threatened species of vulture is frequently found dead in the wild.

 
Eurasian Black Vulture (Aegypius monachus), also known as the Cinereous Vulture.
The vulture is native to Europe and Asia. One large population overwinters in South Korea near the demilitarized zone (DMZ). Researchers examined 20 dead birds found in the area. They analyzed the animals' kidneys, liver and bones for lead and other metals.

They found very high levels of lead in these birds. Fourteen individuals had potentially toxic levels in their liver and kidneys.

Most had higher lead levels in these organs than in their bones, pointing to recent exposures, such as from food. Of the two dozen birds examined, two had tissue lesions associated with lead poisoning. Nineteen were severely emaciated.

The birds showed no evidence of severe trauma; they were not shot or electrocuted and had no lead shot in their stomachs or embedded in their muscles.

The high prevalence of lead and the signs of lead poisoning in this small sample suggest that lead exposure is potentially a very important problem and may be a major cause of mortality for this endangered species.

The results also highlight that wildlife can transport toxic chemicals to new locations where it can then enter different food webs.

The authors suggest that the birds may pick up the poisonous lead during their migration by feeding on other animals that are contaminated with the heavy metal. The lead might come from ammunition used for hunting. South Korea, where the vultures overwinter at the same time as hunting season is in full swing, has no legislation limiting lead shot. Exposure could occur there and/or along migration routes that take the vultures through China to their breeding grounds in Mongolia.

Lead is a naturally occurring metal. Even at low levels it can affect brain and nerve function. The US Environmental Protection Agency considers 10 micrograms/deciliter of lead in blood a safe exposure for people. However, some researchers and health professionals believe there is no safe level, especially for children whose brains are rapidly developing at a time when they may be exposed through peeling paint, dust and toys.

In birds, long term, constant exposure to lead can affect reproduction, immune response, behavior and physiology, which can ultimately affect population size. Lead poisoning in birds of prey is well documented in species around the world. Some of these include vultures in Russia, California condors in the US, bald and golden eagles in the US,  and Canada and white tailed eagles in Germany and Austria.