|Image: Left to right: A white-backed vulture, a hooded vulture and a thick-billed raven in Ethiopia. Credit: Evan Buechley
Species with a defined and effective ecological purpose are in decline, and the less-specialized but more aggressive species that have stepped in to take their place are not only ineffective but also destructive to their ecosystem, which includes humans in this case. Vultures, wild dogs, rabies, and mounds of decaying animal corpses are all part of this narrative. But, in the end, it’s about the ability to conserve ecosystems, even urban ones, in a state of balance that benefits the people who live there.
“Carrion (decaying flesh of dead animals) consumption by vultures is declining, and increasing by most other scavengers, but that increase is not sufficient enough to make up for the loss of vultures,”says Evan Buechley, a University of Utah graduate. “So there’s a gap there. And what happens with that gap is a bit of an unanswered question, but that’s where the problem lies.”
Vultures are well-equipped to deal with the unpleasant remains of death all around the world. Bacteria and insects may overrun rotting carcasses, making them disease hotbeds. Vultures, on the other hand, are quick and effective cleanup crews. They take the carcasses and run them through a highly acidic digestive system that eliminates disease-causing chemicals by devouring carrion. It’s also ideal to have a variety of vultures since some are specialized for tearing away skins, while others, who come in last, actually gobble down the bones.
However, vultures have had their own share of problems in recent decades. Poisons in the carrion they eat, such as lead bullets and medications like diclofenac make them vulnerable.
When Çağan Şekercioğlu, an associate professor in the University of Utah School of Biological Sciences, conducted the first known ecological analysis of all bird species in 2004, he discovered that vultures were the most threatened group of birds (called an ecological guild when the group uses the same or related resources).
“Evan led this project brilliantly and expanded it to the other vulture species of Ethiopia and the Horn,” Şekercioğlu says. “Despite the many challenges, he also decided to study the scavenger communities of the Addis Ababa abattoirs, to quantify the causes and consequences of vulture declines in the region.”
Abattoirs’ feathered “employees”
Vultures are welcome partners in Ethiopian abattoirs (a type of slaughterhouse). Workers carry the leftovers of the corpses – hooves, organs, and bones, for example – to different compounds after slaughtering animals under clean conditions. According to Buechley, it’s a “unique sensory experience.”
Crows, ravens, ibises, and marabou storks are among the flying scavengers who frequent the trash piles. Feral dog groups are among the four-legged visitors. “It’s an urban ecology situation where you have the human food supply meeting and really directly interacting with the wildlife food supply of scavengers,” Buechley adds. “It’s just a really complicated, kind of gross but fascinating system.”
The scientists took note of the different sorts of scavengers who came to the slaughterhouse buffets and estimated how much they ate. Vultures ate more than half of the carrion in the disposal piles initially. White-backed, Rüppell’s, and hooded vultures consumed around 550 pounds (250 lb) of carrion every day on average.
The number of Rüppell’s and white-backed vultures visiting the abattoir disposal yards fell by as much as 73 percent at the end of the five-year research. The number of hooded vulture visits also dropped by 15%. Feral dog detections more than doubled throughout the same period.
“Although we can’t say for sure if the decline represents a population crash or if the vultures are being displaced by dogs and moving away from the abattoirs, either way, this is really concerning,” says Megan Murgatroyd, Interim Director of International Programs for HawkWatch International.
Vultures, on the other hand, cannot afford to lose abattoirs as a feeding source. All the vultures mentioned above are severely endangered. Over the last three generations, the population of Rüppell’s vultures has decreased by over 90 percent (approximately 40 years). Vultures with white backs and hoods also face a similar decline in numbers. They are projected to have decreased by 81 percent and 83 percent, respectively over the three-generation period as well.
Rise in rabies with the decline in vultures
“So it does seem that their disappearance from abattoirs is likely linked to a population crash,” says Murgatroyd. “Vultures need all the help they can get right now, and having to compete with growing dog populations is only making things worse.”
Other scavengers, such as dogs, ibises, and corvids (crows and ravens), are unable to fill the void at the abattoirs. Scavengers consumed roughly 43,000 pounds (about 20,000 kg) less carrion per year in 2019 than they did in 2014 when vultures were more plentiful and dogs were more uncommon.
The growth in dog populations may have a chilling effect on human rabies rates. Vulture populations in India and Pakistan plummeted in the late 1990s. Feral dog populations grew as a result of the uneaten carcasses.
“Unlike a lot of diseases which impact the elderly, rabies disproportionately affects young children, which are the most likely to be bit by rabid dogs,” Buechley says.
The researchers provide a simple suggestion to address the situation: install fences to keep the dogs out. Many abattoirs have already installed fences. “But a pack of feral dogs is really persistent,” Buechley says. “It’s hard to keep hungry animals away from lots of food.”
Fencing out the swarms of dogs might boost carrion consumption rates. Without the dogs to chase away other scavengers, vultures could return in greater numbers to clear up the waste piles more swiftly and effectively. The findings of the study reveal that the extinction of specialised species in an ecosystem is not always compensated for by the emergence of other species.
“The overarching point is that vultures are super important,” Buechley says. “If they decline, we expect there to be pretty profound ecological consequences and there may be increases in human disease burden. And so we should appreciate vultures and invest in their conservation.”
The National Science Foundation, the University of Utah, HawkWatch International, The Peregrine Fund, and the National Geographic Society funded the research, which was published in the Journal of Wildlife Management.