Studying data from 50 species of birds and bats using 17 years of observations has provided insights that challenge the traditional view that flight has a predictable energetic cost that’s always higher than the cost of other types of movement, like swimming or resting. Birds and bats can dramatically reduce the energy needed to travel, the new study shows, by exploiting winds and rising air currents. But to date, these environmental effects have largely been overlooked in estimates of flight costs. Current estimates of the energetic costs of movement across the animal kingdom are largely based on laboratory studies that do not capture the widely variable environmental conditions animals encounter in the wild. In nature, animals routinely exploit moving air and wind to reduce the energy required to travel long distances. These effects are particularly important for flying animals, as winds can dramatically alter how fast they travel, while updrafts can allow soaring birds to almost eliminate the need for flapping their wings and move vast distances at very low energetic costs. Although how atmospheric conditions influence birds’ flight behavior has been studied, the realized effect of these conditions on energy expenditure has not been measured directly. Here, Martina Scacco and colleagues measured the effective cost of transport – the energy flying animals use to travel a given distance – under real-world conditions. Scacco et al. analyzed data from 50 species of birds and bats spanning three orders of magnitude in body size (~12 grams to more than 11 kilograms), using 17 years of high-resolution GPS and acceleration sensor measurements from 850 animals, which was supplemented by radar observations of smaller species. The global biologging dataset allowed the authors to analyze how often animals flapped their wings versus soaring or gliding during sustained flights and compare the energetic costs of flights across species and environmental conditions.
The findings show that the energetic cost of flight in the wild largely depends on how animals interact with the atmosphere. Soaring birds, particularly larger species, can dramatically reduce their energy use by exploiting rising air currents and other atmospheric streams. This, in some cases, reduced flight costs to levels comparable to swimming or even resting. In contrast, frequent flapping species generally have flight costs closer to laboratory predictions and experience greater variation depending on wind conditions. According to the authors, the findings challenge the traditional view that flight has a predictable energetic cost based primarily on body size and biomechanics. Instead, Scacco et al. argue that atmospheric conditions are a fundamental part of flying animals’ energetic landscape and should be incorporated into models of animal movement, migration, and responses to environmental change. “The findings of Scacco et al. encourage researchers to further develop device-tracking technologies and conduct detailed wind-tunnel measurements of the metabolic costs of different flight modes,” writes Anders Hedenström in a related Perspective.
Science
Airflows redefine the cost of aerial transport in the wild
15-Oct-2026