Why Do Vultures Circle? The Science Behind the Omen

While they may not be the prettiest of birds, vultures are a crucial part of a healthy environment. Their ability to quickly locate and remove carcasses keeps bacteria, diseases, and parasites from entering the ecosystem and being eaten and spread by other animals. These feathery scavengers are often seen high overhead searching for food. There is a reason for sayings like “when the vultures start circling,” but the real explanation may surprise you. Learn more about these interesting birds and learn the science behind why vultures circle.

Why Do Vultures Circle?

Circling vultures have been a bad omen throughout history. They are often depicted in media as circling high in the sky, waiting for animals and humans to die. While those rumors and beliefs still persist, there are several good reasons why vultures circle in the air before dropping down to feed.

Conserving Energy

The primary reason vultures circle is to conserve energy. Vultures soar on thermals, which are vertical columns of rising air currents created when the sun heats the Earth’s surface. Warm air is less dense than cold air, so air pockets near the heated ground become lighter and begin to rise.

Thermals are generally shaped like a cyclone. The currents are smaller and weaker near the ground, so the vultures fly in smaller circles the closer they are to the ground. As the air becomes warmer at higher altitudes, the thermals get larger, so the vultures fly in wider circles.

Locating Food

Vultures forage for food from the air. Most vultures, with the exception of the turkey vulture, have a poor sense of smell, but they have exceptional eyesight. When they spot a potential meal, they may circle to assess what they’ve seen to ensure it is actually carrion.

After a carcass has been identified, a vulture will circle the area to make sure that there aren’t any other predators nearby. While vultures may be the most famous carrion-eaters, they aren’t the only ones. They will also determine whether the carcass has already been opened, which makes it easier for the vulture to consume. Checking to see that they are the only scavengers, or at least the largest ones, in the area is a way to ensure their safety.

Signaling Others

A circling vulture also signals to other vultures the location of a carcass and that it is safe to land. They sometimes feed together, especially among family groups. Since turkey vultures have a superior sense of smell, black vultures often follow turkey vultures to a carcass to share in the feast.

Another example is yellow-headed vultures and king vultures in South America. Yellow vultures have a better sense of smell, but their beaks are not strong enough to rip through the tough hide of large animals. So king vultures follow the circling yellow-headed vultures to the site to tear open the carcass so they can all begin feasting.

How Do Vultures Find Food?

There are two primary ways that vultures find food: through sight and smell. As mentioned above, vultures generally do not have a highly developed sense of smell. However, the turkey vulture has one of the largest olfactory bulbs of any bird species in the world. Using this amazing sense of smell, they are able to detect the chemical scents of a decaying carcass, allowing them to locate food more quickly than other vultures.

The majority of vulture species have to rely primarily on sight. However, their eyesight is exceptional. Vulture vision is about eight times better than a human’s. According to the San Diego Zoo, soaring vultures can spot a three-foot-long carcass on the ground from up to four miles away.

How Vultures Eat Rotting Meat Without Getting Sick

Vultures sometimes have to wait for decay to begin before they can tear tough-skinned carcasses, which increases their risk of ingesting toxins. However, they can safely eat rotting meat because of their strong stomach acid and the strong microbes in their guts. Their stomach acid is corrosive, with a pH of between 0 and 1, which is similar to battery acid.

Additionally, vultures have two important microbes in their guts called Clostridia and Fusobacteria that are common in soil, but cause disease in other vertebrates. Clostridia is a microbe that produces toxins, including some that cause botulism and tetanus in humans. Fusobacteria is a flesh-eating microbe, which makes sense given the vulture’s diet. This harsh environment allows vultures to process food with viruses and bacteria that most other animals cannot.