When thinking about the beauty and balance of nature, scavengers may not be the first thing that comes to mind. However, researchers have become increasingly aware of the critical role scavenging plays in ecosystems and food webs. By consuming dead animals, scavengers remove carcasses from the environment. They provide a valuable service that goes well beyond maintaining the beauty of the environment.
For example, if left to thrive in a carcass, bacteria and other pathogens may spread within the local environment and infect other animals, including livestock and humans. Scavengers eliminate these harmful substances from the environment and reduce the spread of disease that may otherwise impact the local food web. These pathogens could also potentially harm human health and the economy.
Nature's Cleanup Crew
Vultures are extremely efficient scavengers. They only eat dead animal carcasses. They are particularly effective at removing pathogens and toxins in the environment because they rapidly consume carcasses before they decay. Additionally, vultures' stomachs contain a powerful acid that destroys many of the harmful substances found in dead animals. Sadly, some toxins are still deadly to these scavengers. These substances are responsible for the majority of vulture deaths over the last 40 years. This trend has landed most vulture species on the endangered list.
Vultures are present on five continents, and their well-being is threatened by toxins on at least three. These deaths are preventable. Some of these deaths are accidental but vultures are also being poisoned on purpose.
Toxins a Threat to Condors, Vultures
In the United States, the California condor population was reduced to only 22 birds in the 1980s because of accidental poisoning. The California condors are a group of vultures whose wingspans can measure up to three meters, almost 10 feet. The vultures fed on remnants of animals field-dressed (removing a killed animal's internal organs) by hunters. These carcasses frequently contained bullet fragments, which were made of toxic lead that killed the condors. Conservation efforts are under way and have been effective. There are currently about 400 California condors; it is still considered one of the rarest birds on Earth.
More recently, in the 1990s, widespread use of the medication diclofenac to treat inflammation in cattle dramatically reduced the vulture population in India. Because few people consume cow meat in India for religious reasons, and because many birds can flock to and consume one cow carcass, each cow that had been recently treated with diclofenac poisoned many vultures. Some studies estimated a decline of more than 90 percent of the Indian vulture population as a result of the use of this drug. India has since banned diclofenac. However, it is still legal in other countries where it may threaten vultures.
Now, the African vulture population is on a decline, in part, because of accidental toxin exposure, but also because of intentional poisoning. Herders poison carcasses to ward off predators such as lions, which pose a threat to livestock. However, vultures are the more common victim. In other circumstances, poachers are targeting vultures by placing poison on carcasses. The poachers do not want vultures flocking around and calling attention to an illegally hunted animal.
Other Dangers for African Vultures
Other threats to the African vulture population include trade of vulture meat and the use of vultures in medicine. They are also dying in accidents involving power lines and wind turbines. These accidents indicate that bird-friendly designs might be needed for implementation of renewable energy infrastructure in these areas.
National Geographic Explorers are working to better understand and protect vultures. Dr. Corinne Kendall is studying behavior patterns of healthy vulture populations in Tanzania. Darcy Ogada has authored academic papers about the African vulture crisis that suggest government policy options for promoting vulture conservation efforts.
An Out-Of-Balance Ecosystem
Vultures are not the only scavengers in nature, but they are often the dominant scavengers due to their ability to scan large areas from the air. As vulture populations decline, other scavengers (like rats or dogs) can move in. This can throw off the ecosystem's balance and be detrimental to wildlife, human health, and the economy.
For example, following the decline of the Indian vulture population, the population of wild dogs expanded rapidly—and with it, the incidence of rabies, an incredibly deadly disease. Approximately 50,000 people died from this rabies outbreak. The associated public health costs were estimated at $34 billion. This sudden population shift can disrupt local food webs. Many scavengers are not as resistant to disease as vultures. They can carry disease back into the environment and towns, exposing people and other animals to pathogens. Carcasses can be infected with not only the rabies virus but other bacteria, viruses, and toxins that are typically annihilated by a vulture's digestive systems. Without a healthy vulture population, the entire food web, and human populations, could be exposed to these pathogens and toxins.
These data and examples show that a single element in a larger food web plays a critical role in overall ecosystem health. The legacy of the vulture and its recent decline highlight threats to wildlife, human health, and the economy that may be present in other natural systems, were they to be disrupted. Fortunately, scientists learn more about our interconnected world each day, and individuals are working to prevent the extinction of animals like vultures.