Photo Credit: flickr | Scott Heron
Edited with Permission by Frontier
Vultures have historically been portrayed as vermin. These birds of prey feed by scavenging on decaying carcasses. The vulture’s physical appearance is also nothing to be desired - they are labelled as the ‘ugly duckling’ of the animal kingdom and do not exactly possess the ‘cute’ characteristics of other endangered species such as tigers and pandas.
Vultures are depicted differently within different cultures. The majority of Western culture views the vulture in disdain and fails to recognise the ecological importance that this species has, due to their unhygienic and ugly appearance. However, these birds are represented very differently in other cultures - for example in Tibet they are used in funeral ceremonies - monks lay deceased bodies to rest and allow vultures to recycle the remains.
The Ecological Role of Vultures
As the garbage men of the natural world, vultures help to prevent the spread of disease, maintaining equilibrium within the ecosystem. They are physiologically adapted to digest meals that would kill a human. Their corrosive stomach acid is able to neutralise natural toxins found in decaying flesh, meaning they can consume prey riddled with anthrax, botulinum toxins, rabies and hog cholera. By clearing the ground of carcasses, they reduce the risk of disease being transferred to other species including humans.
However, vulture populations are rapidly declining throughout the world. This is largely caused by poisoning from poachers and lead ammunition used for sport hunting. Vultures can act as indirect indicators of illegal poaching activity – they are attracted to carcases of other animals and often circle above them, which informs the authorities of the poachers’ presence. For this reason poachers often poison the carcasses of both rhino and elephants after removing their ivory and horns to prevent the risk of being detected by rangers - allowing them to continue their illicit activities. Unfortunately this practice has become increasingly popular among poaching groups due to the demand for ivory and rhino horn.
Another practice which is damaging vulture populations is the act of farmers leaving out poisoned livestock carcasses to deter larger predators such as lions and cheetahs away from their land. Vultures have consequently been negatively impacted by foraging on these remains.
The direct and indirect effects of poisoning have caused a steep decline in many vulture populations with the majority of species now being classified as endangered. Of the 23 species of vulture 16 are considered to be vulnerable, threatened or endangered, with some populations having declined by as much as 90%. Other scavenging species such as feral dogs, rats and blowfly larvae have been documented to have significant population increases when vultures fail to remove debris, by occupying vacant environmental niches. These alternative scavengers pose larger health risks to humans due to many being carriers of rabies. For example in India between 1993 and 2006, a rabies outbreak cost the government US$34 billion. Despite efforts to curb outbreaks India still has one of the highest rabies counts in the world.
Photo Credit: Wikipedia Commons | Babbage
Lead ammunition - Vultures Under Fire
Intentional poisoning remains the biggest threat to vulture populations worldwide. However a new study shows that lead ammunition could be just as deadly. In Botswana the lead pellets left behind in the carcasses of herbivores targeted by game hunters could also be poisoning vultures. The African white-backed vulture (Gyps africanus) is already severely threatened; its population has decreased by 90% across its home range and this species is now considered critically endangered on the IUCN Red List.
Historically, Southern Africa has always been a hub for hunting, especially in Botswana for both meat and sport. It is common for hunters to discard the internal organs of their kills known as or even whole carcasses in the bush – known as ‘gut piles’.
“Hunting is such a huge industry in Africa which led us to investigate whether vulture populations in Africa could be at risk of poisoning from ingesting spent ammunition,” said Rebecca Garbett, a researcher with the non-profit organisation Raptors Botswana and a doctoral student at the University of Cape Town, South Africa. “When an animal is shot, the lead bullet will release fragments widely throughout the carcass. Vultures can then ingest fragments while they are feeding.”
To investigate this issue further and to calculate the potential risk from lead poisoning ingestion Garbett and her team captured and drew blood from 566 vultures in 15 different locations in both non hunting and hunting locations within Botswana between 2012 and 2015. An annual survey was conducted throughout the year to determine if blood lead levels differed between the hunting season from April to November and the non-hunting season from December to March.
“Thirty percent of almost 600 white-backed vultures that we tested had elevated blood lead levels above what could be considered background exposure,” Garbett said. The team found a significant relationship where vultures captured from hunting areas contained much higher concentrations of lead in their blood than those that were captured from non-hunting areas. The results therefore suggest that lead ammunition is likely responsible for the difference in blood lead levels. Arjun Amar, a conservation biologist at the University of Cape Town, who oversaw Garbett’s study said ”there is no other logical explanation for this pattern other than these higher levels were linked to lead ammunition associated with hunting.”
This theory was further reinforced by Vinny Naidoo, a professor of veterinary pharmacology at the University of Pretoria, South Africa. He states that “lead is a neurological toxin and commonly affects the brain,” and that “the most common clinical signs are weakness, stargazing, blindness, seizures, depression and inability to walk.” Although Naidoo acknowledges that there is a strong link between ammunition and the lead concentrations in blood, he also suggests that other variables may also be leading to high blood lead levels. One factor outlined was high concentrations of lead in local soils, most likely caused by heavy usage of leaded fuels that were used in Southern Africa until 2006.
Moreover, the most surprising finding from Garbett’s study was that blood lead levels of vultures in both hunting and non-hunting areas increased after the 2014 hunting ban. However researchers believe that the increase was due to vultures feeding on carcasses inside private game farms where hunting was legal.
Another reason that identifying the source of lead in blood proves to be a big challenge is the movement of some species of vulture. For example the “Lappet-faced vultures (Torgos tracheliotos) that were tagged in Botswana - we know they spent time in all of the five countries surrounding Botswana,” Amar said. These are Namibia, South Africa, Zimbabwe, Zambia and Angola.
Photo Credit: Wikipedia Commons | Yathin sk
What can be done?
The vulture problem is international and has also been associated with the decline of the Californian condor (Gymnogyps californianus). California has consequently outlawed the use of lead ammunition for hunting within the condor’s range. Despite the ban on lead ammunition, lead poisoning is still the biggest threat to the Californian condor according to Myra Finkelstien and Donald Smith’s study from the University of Santa Cruz, where they were able to match the chemical makeup of locally used ammunition to the lead found in birds’ blood. The findings made by Finkelstein and Donald’s study provided sufficient evidence that persuaded the California Fish and Game Commission to ban the use of lead ammunition for all wildlife hunting state-wide in October 2013. This ban is due to be operational by 2019.
Garbett and Amur are also now calling for a ban in Southern Africa based on their findings. “A regional ban on the use of lead ammunition is needed but a national ban would be a start.” Going forward, more evidence is required to fully understand the impacts of lead ammunition, but in a race against time for the vulture, lead ammunition should be a relatively simple issue to address. There are other ammunition alternatives that are both non-lead based and have been globally accredited by hunters.
Although the vulture is one of the uglier members of the animal kingdom we cannot deny its value in a complex ecosystem. We must conserve these endangered birds to preserve healthy ecosystems for other wildlife species and ourselves.