A new study has revealed that some large birds rely on wind currents to fly through the air, without any need to flap their wings. The researchers discovered that the world’s heaviest soaring bird, the Andean condor, only flaps its wings for one percent of the time spent flying.
Led by Swansea University, the experts set out to investigate how the flight efforts of birds vary depending on environmental conditions. The research will provide new insight into the soaring capacity of large birds and the specific conditions that make flight costly.
The team used flight-recorders on Andean condors to track their wing movement during flight. The high-tech recorders logged every wingbeat, twist, and turn as the birds searched for food.
The researchers found that more than 75 percent of wing flapping was associated with take-off. Once in the air, however, the birds sustained soaring for extended time periods in a wide range of wind and thermal conditions. One bird even clocked five hours without flapping, covering more than 100 miles.
“Watching birds from kites to eagles fly, you might wonder if they ever flap,” said study co-author Dr. Hannah Williams. “This question is important, because by the time birds are as big as condors, theory tells us they are dependent on soaring to get around.”
“Our results revealed the amount the birds flapped didn’t change substantially with the weather. This suggests that decisions about when and where to land are crucial, as not only do condors need to be able to take off again, but unnecessary landings will add significantly to their overall flight costs.”
Professor Shepard pointed out that all of the birds observed in the study were immature, which demonstrates that low investment in flight is possible even in the early years of a condor’s life.
Upon further analysis, the experts recognized that the birds faced challenges as they moved between weak thermals. The Andean condors flapped more as they reached the end of the glides between thermals when they were likely to be closer to the ground.
“This is a critical time as birds need to find rising air to avoid an unplanned landing. These risks are higher when moving between thermal updrafts,” said study co-author Dr. Sergio Lambertucci.
“Thermals can behave like lava lamps, with bubbles of air rising intermittently from the ground when the air is warm enough. Birds may therefore arrive in the right place for a thermal, but at the wrong time.”
“This is a nice example of where the behavior of the birds can provide insight into the behaviour of the air.”
The study is published in the journal Proceedings of the National Academy of Sciences.