Birds fly in circles primarily to ride columns of warm rising air called thermals, which let them gain altitude without flapping their wings. This saves enormous amounts of energy. Gliding flight costs roughly 10 times less energy than flapping, and for some species, the energy spent gliding is statistically indistinguishable from the energy spent sitting still on a nest. But energy savings aren’t the only explanation. Depending on the species and situation, circling can also serve as a way to scan for food, signal other birds, gain altitude before a long migration, or navigate wind patterns over the ocean.
Riding Thermals to Stay Airborne
The most common reason birds circle is to exploit thermals. A thermal is a rising mass of air that forms when the sun heats the ground unevenly. Dark pavement, rocky outcrops, and bare fields absorb more heat than surrounding areas, warming the air above them. That warm air rises because it’s lighter than the cooler air around it, creating an invisible column of lift. These columns are relatively narrow, so a bird that wants to stay inside one has to fly in tight circles rather than in a straight line.
Tracking data from white storks shows just how precise this circling is. The typical circling radius is about 18 to 22 meters, and each full circle takes roughly 12 to 15 seconds. In smaller thermals, storks slow down and bank more steeply to stay within the rising core. In larger thermals, they fly faster and bank less. Birds actively optimize their position, adjusting bank angle and airspeed at different altitudes to compensate for changes in the thermal’s width and the thinning of the air higher up.
The energy payoff is dramatic. In kittiwakes, flapping flight burns energy at about 5.5 times the basal metabolic rate, while gliding costs only 0.8 times that baseline. That means flapping is nearly seven times more expensive than gliding. For large soaring birds like eagles, vultures, and storks, the math is even more favorable because their body size makes sustained flapping extremely costly. The core principle is simple: dwell in updrafts, avoid downdrafts, and let the atmosphere do the work.
Scanning for Food From Above
Vultures are the birds most people picture when they think of circling, and for good reason. Vultures ride thermals to reach high vantage points, then survey the ground below for carcasses. They can glide for several hours and cover vast stretches of land without spending significant energy. Circling at altitude gives them a wide visual sweep that would be impossible from the ground or from low, straight-line flight.
Circling also works as a social signal. When one vulture spots food and begins circling above it, other vultures in the area notice the behavior and converge on the same spot. This chain reaction can draw dozens of birds to a single carcass. Hawks and eagles use a similar strategy, circling at height to spot small mammals or reptiles moving through open terrain below.
Kettles During Migration
During migration season, you might see dozens or even hundreds of large birds circling together in a swirling mass. This formation is called a kettle. Raptors like hawks, eagles, and broad-winged hawks form kettles, and so do storks and white pelicans. The birds aren’t just socializing. They’re all exploiting the same thermal to gain altitude cheaply before peeling off and gliding toward the next thermal along their route.
This “thermal hop” strategy makes long-distance migration far less exhausting. A migrating golden eagle, for example, averages about 965 meters above ground during flight, with altitudes ranging from 200 to over 2,500 meters. The bird climbs by circling in a thermal, then glides forward and downward until it finds the next one, repeating the cycle across hundreds of kilometers. Without thermals, a bird that size would need to flap constantly, burning fuel it can’t afford to lose on a journey that may span entire continents.
Dynamic Soaring Over the Ocean
Not all circling relies on thermals. Albatrosses and other large seabirds use a different technique called dynamic soaring, which harvests energy from wind speed differences at various heights above the water. Wind is slower near the ocean surface (due to friction) and faster higher up. Albatrosses exploit this gradient by flying in a repeating loop: climbing into the wind, curving at the top to turn downwind, descending toward the waves, then curving again near the surface to face back into the wind.
Tracking data from 16 wandering albatrosses in the southern Indian Ocean confirmed this four-phase pattern. The primary energy gain happens during the upper curve, where the bird turns from flying into the wind to flying with it, picking up speed from the stronger winds at altitude. The energy loss happens during the lower curve near the sea surface, where wind speeds are weakest. By repeating this looping pattern continuously, albatrosses sustain non-flapping flight for thousands of kilometers. The loops aren’t perfect circles like thermal soaring, but winding, curving paths that look circular from a distance.
Flock Coordination and Predator Response
Smaller birds sometimes circle in tight flocks for reasons that have nothing to do with thermals. When a predator appears, flocking birds may wheel in coordinated circles as a defense mechanism. The rapid, synchronized turning creates a confusing visual effect that makes it harder for a hawk or falcon to single out one individual. Research from the University of Maryland has shown that an avoidance signal from a single bird closest to the danger can spread through the entire flock like a wave. One bird turns, its neighbors detect and match the movement almost instantly, and the signal propagates outward. The flock itself acts as the medium through which information travels, producing the near-simultaneous turns that make circling flocks look like a single organism.
Circling Before Landing
You may also notice birds circling a specific spot before touching down. Pigeons and other birds circle a landing zone to assess wind direction, check for obstacles, and adjust their speed and body angle for a safe approach. Turning at low speeds is biomechanically demanding. Pigeons redirect aerodynamic forces during a turn by reorienting their bodies, prioritizing the change in flight path first and then readjusting their body position for forward flight afterward. Circling a landing area gives a bird time to slow down gradually and line up an approach, much like an airplane making a pattern before landing at an airfield. At higher speeds, birds can adjust their wings and tail to steer more easily, but near a landing site where they’re braking, the repeated circling serves a practical aerodynamic purpose.