Andean condors are the heaviest flying bird in the world, with a single individual weighing up to about 16 kilos (or 35 pounds). According to new research, when it comes to keeping these heavy bodies up high, the sky is the limit, it seems.
Taking off from the ground is the most difficult part for these South American condors (Vultur gryphus), but once the giant birds are in the air, researchers have found that they hardly ever flap their wings. Instead, they glide, flying for up to 99 percent of their flight time, primarily in winds and updrafts.
The researchers obtained more than 230 hours of cataloged flight time by connecting bio-recording devices, or ‘daily diaries’, to eight juvenile condors. In all that time, only 1 percent was spent flapping, and most was just for takeoff.
“The extraordinary low inversion in flapping flight was observed in all people, which is remarkable since none were adult birds,” the authors write.
“Therefore, even relatively inexperienced birds operate for hours with minimal need for flapping.”
A young condor actually flew for more than five hours without flapping its wings once, covering over 170 kilometers (100 miles) using only drafts.
“The finding that [Andean condors] Basically, they hardly ever flapped their wings and simply flying is mind-blowing, “David Lentink, a bird flight expert at Stanford University, who was not involved in the study, told The Associated Press.
Flying birds are usually the largest, because the energy required for powered flight is much higher for heavier creatures. While lighter species, like hummingbirds, flap their wings at a dizzying pace, the condor’s ‘marine counterpart’, the albatross, spends between 1.2 and 14.5 percent of its flight flapping its wings slowly.
The Andean condor does even less. For example, on a 50-minute trip, juvenile condors spend almost the same amount of energy gliding, rising, and flapping occasionally as they do during their 3.3-minute takeoff.
In fact, the authors found that the cost of flapping these large birds was about 30 times greater than their resting metabolic costs, meaning that they are probably as energy-efficient as sprinting for mammals.
Using continuous data from the bio-recorders, the researchers identified each and every wing beat of the eight juvenile condors in various wind and thermal conditions.
Even in the mountains, where there are complex airflow interactions, these young condors were able to navigate invisible air currents with very little movement.
“Human glider pilots can fly all day if conditions are right, so in some ways the performance of the condor may not seem surprising,” biologist Emily Shepard of the University of Swansea told the BBC.
“But the glider pilots look at the weather and decide whether or not it is good to fly.”
Condors do not have that luxury. They usually shoot to find food, which is not always found in easily accessible places, especially when air currents are mainly used to get there.
While it takes a lot of energy for condors to take off, it requires finesse to land, making these giant birds selective about where they land.
If a condor wanted to head towards a juicy body on the ground, for example, it would have to jump from updraft to updraft, moving into the warm updraft. Sometimes closing those gaps requires occasional flapping.
Furthermore, these atmospheric “hot spots” are not always hot. Their power and frequency change with the weather, topography, and season, so predicting them isn’t always easy when they head ashore.
“This is a critical moment since birds need to find ascending air to avoid an unplanned landing,” explains Sergio Lambertucci, a biologist at the National University of Comahue in Argentina.
“These risks are greatest when moving between thermal updrafts. Thermal ones can behave like lava lamps, with air bubbles rising intermittently from the ground when the air is warm enough. Therefore, birds can reach the Right place for a thermal, but in the wrong time. “
Even in winter, when conditions for strong winds and thermal updrafts are not so good, the authors found that Andean condors are still unwilling to take a path that forces them to flap their wings.
“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 significantly increase their overall flight costs,” says movement ecologist Hannah Williams, now in the Max Planck Institute for Animal Behavior.
Understanding how giant birds navigate invisible obstacles in the sky not only informs us about atmospheric conditions, but can also shed light on how absolutely massive extinct birds, such as Argentavis magnificensThey once held their 72-kilogram bodies up high.
“It has always been assumed that Argentavis it would have been incapable of a sustained flapping flight and was therefore entirely dependent on the rise, “the authors write.
It is likely, therefore, that they too raised the heavens like the Andean condor, flapping their wings as a safety net, and only when absolutely necessary.
The study was published in PNAS.
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