Swifts are among the fastest migrating small birds around.

When they aren’t breeding, common swifts stay in the air most of the time–up to 10 months of the year.

Scientists had thought they travel about 500 kilometers per day on average. Now, new evidence reported in the journal iScience on shows that’s a conservative estimate.

According to new tracking data, common swifts travel 570 kilometers (more than 350 miles) on an average day–but they are capable of going much farther and faster. The maximum recorded distance in the study was more than 830 kilometers (more than 500 miles) per day over nine days.

Swifts manage these feats by using a fly-and-forage strategy, which works for species that can easily find food along the way instead of loading up before a long trip. Swifts rely primarily on flying insects for food.

The researcher from Lund University in Sweden used miniature tracking technology based on geolocation by light to track adult breeding swifts from one of the most northern breeding locations in Europe. They were surprised at just how fast the birds could travel.

Susanne Åkesson explained:

“We have discovered that common swifts breeding in the most northern part of the European breeding range perform the fastest migrations of swifts recorded so far, reaching above the predictions.

“The swifts seem to achieve these high speeds over substantial distances–on average about 8,000 kilometers one way–in spring by using a mixed migration strategy, with fueling at stopover and a fly-and-forage strategy, meaning they feed and fuel a bit each day.”

Swifts also use favourable winds. Susanne Åkesson added:

“They do not react directly to local winds but to what they expect to find along the route ahead during the next few days.”

It’s not clear how the swifts can forecast the wind and make decisions based on it, but Åkesson suggests that it’s possible they rely on air pressure associated with passing weather systems. However they do it, this selective departure strategy means the swifts can gain an extra 20% support from tailwinds in spring as compared to the fall. They get the most benefit in terms of speed for crossing the Sahara and the Mediterranean Sea.

“The airspeed of common swifts is not exceptional (about 10 meters/second) as compared to other bird migrants,” Åkesson says.

“But these strategic adaptations contribute to the high overall migration speeds. In addition, their selective use of tailwinds promotes even higher migration speeds, which may explain how they reach above the predicted maximum speed during spring migration.”

The researchers note that swifts’ lifestyle and reliance on insects may put them at risk due to pesticide use by humans. Climate change and changing weather or wind patterns might also have unknown impacts on these extreme fliers.

Åkesson says they’ll continue to study and track swifts in different parts of the world. They also hope to learn more about the physiological adaptations that enable the swifts’ highly mobile lifestyle.

This work was supported by the Carl Trygger’s Foundation, the Swedish Research Council, and the Centre for Animal Movement Research (CAnMove), which is funded by a Linnaeus grant from the Swedish Research Council and Lund University.

See also: RSPB Swift Mapper