The sight of a large, dark bird silently orbiting high above the landscape is a common observation. This circling behavior, primarily associated with scavengers, is a sophisticated, energy-saving strategy that allows these birds to master the atmosphere. The circling combines atmospheric physics with an unparalleled search technique, ensuring they can cover vast areas with minimal effort. This flight pattern is an adaptive solution for finding dispersed food sources in an expansive territory.
Defining the Buzzard and the Behavior
The term “buzzard” can be confusing because its meaning changes depending on the geographical region. In North America, it colloquially refers to vultures, specifically the Turkey Vulture and Black Vulture. In the Old World, particularly Europe, “buzzard” formally refers to broad-winged hawks of the Buteo genus, such as the Common Buzzard.
Regardless of the species, circling is a form of soaring that conserves energy. Vultures and Buteo hawks are specialized for this flight style due to their large wingspans and light bodies relative to their size. Soaring allows these birds to remain airborne for extended periods without the physical exertion of flapping their wings, which is costly for large raptors. This adaptation makes continuous circling possible, as they trade muscle power for the power of the wind.
Harnessing Air Currents (Thermals)
The primary mechanical reason for the circling pattern is the exploitation of rising columns of warm air, known as thermals. Thermals form when the sun heats the ground, warming the air directly above it. This warm air is less dense than the surrounding cooler air, causing it to rise in a cylindrical column, much like a chimney.
To gain altitude effortlessly, the bird enters this column of rising air and begins to circle. Circling is necessary because it allows the bird to remain within the narrow core of the thermal, where the lift is strongest. By flying in a continuous spiral, the bird is constantly carried upward, converting the atmospheric energy into potential energy, or altitude, which can then be used for long-distance travel. The rate of climb can often reach several meters per second, enabling them to ascend hundreds of meters without a single wing flap.
Once the bird has reached a sufficient height, or the thermal weakens, it leaves the rising column and glides in a straight line toward the next thermal. This soaring-and-gliding strategy is highly efficient, allowing the bird to cover vast distances while minimizing the energy expenditure that would be required for powered flight. The time-consuming ascent in the thermal is necessary to build up the potential energy required for the long glide to a new search area. This process is why the circling is usually observed during the warmest parts of the day when thermal activity is at its peak.
Locating Food Sources
The altitude gained by riding thermals serves the purpose of efficiently scanning the landscape for food. From a great height, the bird’s field of view expands exponentially, allowing it to survey many square miles of territory. This is important for scavengers, as carrion is a food source that is randomly and sparsely distributed across the environment.
Vultures possess exceptionally acute vision, with some Old World species, such as Rüppell’s Griffon Vulture, potentially spotting small objects from distances exceeding 10 kilometers. This visual specialization is centered on detecting subtle signs of a carcass, often from thousands of feet in the air. The continuous circling motion facilitates a methodical, 360-degree scan of the ground below, ensuring no potential food source is missed as the bird is carried upward.
While some scavengers, like the Turkey Vulture, also use a keen sense of smell to locate carrion, the primary search technique for most circling raptors is visual. When a bird spots a potential food source, it will often continue circling, but it will begin to descend in a tighter spiral to confirm the find and prepare for landing. Circling is a persistent, wide-area search strategy that converts a high-altitude advantage into a successful foraging opportunity.
Group Dynamics and Communication
When large numbers of buzzards circle together, the behavior takes on a social dimension related to communication and group foraging. Once an individual bird discovers a strong thermal, its circling flight acts as a visible beacon to other raptors in the vicinity. Other birds see this circling movement and converge on the location to gain altitude themselves, creating a visible “kettle” of rising birds.
Similarly, when a buzzard spots a carcass and begins its descent, this change in flight pattern immediately signals a food discovery to others. Vultures are highly social scavengers, and the sight of birds spiraling down is a powerful visual cue that draws others from miles around. This coordinated response ensures that a found resource is quickly shared by the group, which improves foraging success for all individuals. This strategy links energy-saving flight mechanics with efficient social communication about food availability.