Common swifts are even faster than previously realized

Common swifts travel more than 350 miles on an average day and have the capacity to travel even farther, according to a new study from Cell Press. The researchers recorded a maximum distance of more than 500 miles per day over nine days.

“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,” said Susanne Åkesson of Lund University in Sweden. 

When they are not breeding, common swifts stay in the air most of the time up to 10 months of the year. Prior to this study, scientists estimated that the birds travel an average of about 500 kilometers, or 310 miles, per day. The new research suggests that this is a conservative estimate.

“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.”

The researchers used miniature tracking devices to monitor adult breeding swifts from one of the most northern breeding locations in Europe. The team was able to recover many of the tracking devices after one migration season. 

The tracking data confirmed that northern breeding swifts reach exceptionally high migration speeds. But the researchers did not expect to find that the birds could travel at the rates that were recorded. 

Swifts manage to travel quickly by using a fly-and-forage strategy, which works for species that can easily find food along their journey, such as flying insects. 

“The strategy will substantially reduce the cost of transport since they do not need to carry so much fuel, which will increase the realized speed of migration,” explained Åkesson.

According to the researchers, the swifts also have another trick – they seem to time their departures for migration so that they coincide with favorable winds. 

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

While it is not yet clear how the swifts can forecast the wind and make decisions based on it, Åkesson suggests that they may rely on air pressure associated with passing weather systems. The wind strategy helps the swifts gain an extra 20 percent of support from tailwinds in the spring compared to the fall. 

“The airspeed of common swifts is not exceptional (about 10 meters/second) as compared to other bird migrants,” said Åkesson. “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 experts noted that pesticide use may pose a threat to swifts, considering their reliance on insects. Climate change and shifting weather patterns may also have unknown effects on the birds. 

Åkesson said her team will continue to study swifts in different parts of the world. The researchers hope to learn more about the physiological adaptations that support the swifts’ highly mobile lifestyle.

The study is published in the journal iScience.

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By Chrissy Sexton, Earth.com Staff Writer