An Andean condor flaps 0.1% of the time while a swan of the same weight flaps 99%

Two birds can weigh the same, about 11 kilograms each, and still live in entirely different energy economies. An Andean condor spends only 0.1 percent of its flight time flapping its wings, while a trumpeter swan flaps for 99 percent of its time in the air. A study published October 15 in the journal Science puts a number on what that difference costs: the condor’s energy bill per kilometer is roughly a fifth of the swan’s.

The tech news worth your time: 400,000+ professionals from Google, Apple and OpenAI read Techpresso, a free daily email with the most interesting tech news and insights.

Subscribe to Techpresso free →

We may earn a commission if you sign up.

The comparison is the sharpest example in a much larger tracking project, and it overturns a tidy textbook idea. For decades, flight has been treated as a single, fairly uniform price per unit of body mass, ranked as more expensive than swimming and cheaper than running. The new work argues that the air itself, not just the animal moving through it, sets the price, and that the same wing can be a bargain or a burden depending on the wind.

Condor versus swan, kilometer by kilometer

According to a news release from the Max Planck Institute of Animal Behavior issued through EurekAlert, the condor’s cost of transport was 79 percent lower than the swan’s. Both birds weigh about 11 kilograms, which removes body size as an explanation. What differs is how each one gets lift. The condor climbs on rising columns of warm air and glides between them, while the swan has to generate lift with continuous muscle power.

Martina Scacco, the first author, who is listed with the Swiss Federal Institute WSL, framed the broader lesson in terms of habitat. In the release she said that for flying animals the sky might just look like background, when it is in fact an essential resource. Emily Shepard of Swansea University, a senior author, put the soaring side bluntly: “Soarers are masters at extracting energy from the environment.” The other senior author is Kamran Safi of the Max Planck Institute of Animal Behavior.

The condor is no outlier among large soaring birds. The release says seven vulture species in the dataset flew a combined 128,000 days and more than 4.3 million kilometers while flapping only between 0.1 and 7 percent of their flight time. Soaring can be cheap enough to rival, or in some cases beat, the cost of swimming, which contradicts the usual ranking.

What 850 tracked animals showed about wind

The result rests on a large dataset. The release describes GPS and accelerometer records from 850 birds and bats belonging to 38 species, gathered over 17 years, plus four years of radar data covering 12 size classes. Animals ranged from about 12 grams to more than 11 kilograms, and the release says 68 researchers contributed data. The full study covers 50 species, a scale that let the authors compare how flapping, gliding and soaring behave in real weather rather than in a wind tunnel.

Air does not only help, according to Safi. “Air can drive flight costs up as well as down for flappers,” he said in the release. Small and medium birds that flap through variable conditions pay a penalty when they meet headwinds, because they cannot simply wait for a thermal. That finding turns the wind from background noise into a variable as important as wingspan or mass in estimating how much food a migrating animal needs. For conservationists, that matters because routes, stopovers and feeding grounds are planned around energy budgets that may have been mis-estimated for years, in either direction, by animals of very different build.

Earlier condor work and where the field goes

The new paper builds on years of work from the same groups. A 2020 Swansea University announcement described Andean condors flapping for about 1 percent of their flight time, with more than 75 percent of that flapping happening at take-off, and one bird staying aloft for five hours and about 172 kilometers without a single wingbeat. Those condors flapped more near the end of glides between thermals, when they were likely closer to the ground, and the researchers noted that unnecessary landings add significantly to flight costs, so deciding when and where to touch down matters as much as how to climb. All the birds in that earlier study were immature, which showed that low flight investment is possible early in life.

The Max Planck Institute’s cost-of-transport project page describes the goal as a first assessment of how the physical environment affects flight costs in the wild, and notes that the effect differs by body shape and mass. Shepard’s research, outlined on her Swansea University staff page, centers on how weather and landscape change the energy cost of flight, using animal-attached tracking devices and models. Her 2024 paper in Current Biology found that latitudinal gradients in air density create what the page calls invisible topography at sea level, another way in which the atmosphere quietly shapes what a wingbeat costs. The full paper, titled “Airflows redefine the cost of aerial transport in the wild,” is available through its Science digital object identifier.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.