Turkey vultures (Cathartes aura) are a common sight across the Americas, known for their distinctive soaring patterns. These large, dark birds with reddish, unfeathered heads are often seen tracing wide circles high in the sky. Their flight appears wobbly or teetering, as they hold their wings in a shallow V-shape, a posture known as a dihedral. This behavior often prompts curiosity about its purpose.
Pinpointing Food Sources
A primary reason turkey vultures circle is to locate food. These birds are scavengers, feeding almost exclusively on carrion. Unlike many other birds, turkey vultures possess an exceptional sense of smell, highly developed for detecting gases from decomposition. Their olfactory bulb is notably large compared to other bird species.
This acute sense of smell allows them to detect specific chemicals, such as ethyl mercaptan, produced during decomposition. They can pinpoint these scents from hundreds of feet, or even miles, away. Circling enables them to systematically cover large areas, allowing their keen sense of smell to home in on the source of the odor below. This specialized adaptation gives them an advantage in finding hidden food, even something as small as a dead rat concealed beneath leaves.
Harnessing Natural Air Currents
Turkey vultures are masters of soaring flight, and their circling behavior is key to energy conservation. They take advantage of rising columns of warm air called thermals, created as the sun heats the ground. By circling within these thermals, vultures can gain altitude without needing to flap their wings, much like an elevator to the sky. This allows them to stay aloft for extended periods, sometimes for hours, with minimal energy expenditure.
Their V-shaped wing formation provides stability and balance, particularly in turbulent air. This efficient soaring allows them to cover vast territories, often hundreds of miles in a single day, while searching for their next meal. When thermals are weak, such as on overcast days or early mornings, vultures may flap their wings more often, demonstrating their reliance on these air currents for efficient travel.
Collective Gathering and Roosting
Beyond finding food and conserving energy, turkey vultures also circle for social reasons. A group of vultures soaring together is often referred to as a “kettle.” When one vulture locates a food source, its circling descent can signal the presence of a carcass to other vultures. This communal behavior ensures that multiple birds can converge on and share a large food supply.
Circling can also be observed when vultures are approaching their communal roosting sites. These birds often gather in large numbers to rest overnight in trees or on communication towers. They use thermals to efficiently travel to these nighttime resting places, with circling being part of their approach or departure from these sites. This collective flight helps them maintain social interactions and aids energy conservation.