When you think 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 scavengers play in ecosystems and food webs.

All the interconnected food chains in an ecosystem make up a food web. By consuming dead animals scavengers remove carcasses from the environment. This is a valuable service that goes beyond keeping the environment clean and beautiful.

Scavengers Help Prevent Spread of Diseases

Scavengers prevent diseases from spreading. For example, if left alone, bacteria on a carcass could spread throughout the local food web infecting animals, including livestock and humans. Scavengers remove these harmful substances from the environment, protecting animal and human health.

Vultures are one of the most effective scavengers. They only eat dead animal carcass. They remove bacteria and other poisons in the environment quickly, consuming carcasses before they decay. Additionally, their stomachs contain a powerful acid that destroys many of the harmful substances found in dead animals. Sadly, some poisons are still deadly to these scavengers. Poisons are responsible for the majority of vulture deaths over the last 40 years. Most vulture species are on the endangered species list.

Poisons Pose Threat to Vultures

Vultures are present on five continents, and their health is threatened by poisons on at least three. Some of these deaths are accidental, but vultures are also being poisoned on purpose.

In the United States, the California condor population was reduced to 22 birds in the 1980s. California condors are a group of vultures whose wingspans can measure up to three meters, almost 10 feet. These large birds were accidentally poisoned when they fed on the carcasses of animals field-dressed (removing a killed animal's internal organs) by hunters. These carcasses often contained bullet fragments made from toxic lead, which killed the condors. Conservation efforts are unde rway and have been effective. Conservation is the protection of animals and their natural habitats. Although there are now over 400, the California condor is still considered one of the rarest birds on Earth.

In the 1990s the use of the medicine diclofenac to treat cattle dramatically reduced the vulture population in India. Because many birds feed on one cow carcass, each dead cow recently treated with diclofenac could poison many vultures. Also, most people in India don't eat cow meat for religious reasons. Therefore, there were many cow carcasses available to vultures. Some studies estimated a loss of more than 90 percent of the Indian vulture population because of the use of this drug. India has since made the use of diclofenac illegal. However, it is legal in other countries where it may still threaten vultures.

The Trickle-Down Effect in the Food Chain

Now, the African vulture population is declining. This is due to both accidental and intentional poisoning. Herders poison carcasses to keep away predators like lions, which pose a threat to their livestock. However, vultures are the more common victim. Poachers kill vultures on purpose by placing poison on carcasses. The poachers do not want vultures flocking around and calling attention to animals they have illegally hunted.

Other threats to the African vulture population include vulture meat trade and the use of vultures in medicine. They are also dying in accidents involving power lines and wind turbines. This suggests more work needs to be done to build energy structures that will not harm birds.

National Geographic Explorers are working to better understand and protect vultures. Dr. Corinne Kendall is studying behavior patterns of healthy vulture populations in Tanzania. Tanzania is in eastern Africa. Darcy Ogada has written academic papers about the threats to African vultures. In her work she provides actions the government could take to promote vulture conservation efforts.

Lack of Vultures Can Throw Off Nature's Balance

Vultures are not the only scavengers in nature. However, they are often the most effective because they can scan large areas of land from the air. As vulture populations decline, other scavengers (like rats or dogs) move in. This shift in scavengers can throw off the ecosystem's balance and endanger wildlife and human health.

For example, following the decline of the Indian vulture population, the population of wild dogs grew rapidly. The incidence of the deadly disease rabies also grew. Approximately 50,000 people died from this outbreak and the public health costs were estimated at $34 billion.

Disruption in the Food Web

This type of sudden population shift can affect local food webs. Many scavengers are not as resistant to disease as vultures. Because of this, they can carry disease back into the environment, exposing people and wildlife. In addition, carcasses can be infected with not only the rabies virus but other bacteria that are typically destroyed by vulture digestive systems. Without a healthy vulture population, the entire food web and human populations, could be exposed to poisons.

These examples show that a single element in a larger food web plays a critical role in overall ecosystem health. The story of the vulture shows how threats to wildlife and human health could occur if natural systems are disrupted. Fortunately, scientists learn more about our interconnected world each day and individuals are working to prevent the extinction of animals like vultures.