Small birds are more energy efficient flyers than bats because birds have more energy efficient wing strokes.
Researchers previously believed this was due to air resistance created by the bats’ ears.
But now biologists at Lund University in Sweden have discovered that the wings of small birds in their most elevated position interact in a completely different way compared to the wings of bats.
As the birds flap their wings downwards, they create a single large air vortex ring behind themselves rather than two small ones.
More Energy Efficient Flying Long Distances
“This makes the airflow slower and the aerodynamics less energy-demanding. This, in turn, means that birds are more suitable for flying long distances than bats,” says Christoffer Johansson, a biologist at Lund University.
According to Johansson, the new results should be incorporated into existing models of how much energy birds consume when they fly.
Among other things, these models are used to calculate how far birds can migrate.
The results are based on studies of the European pied flycatcher flying in the Lund University’s wind tunnel while the researchers studied the movements of the air behind the bird.
Not Perfect Little Flying Machine
Although the researchers have shown how the interaction of the small birds’ wings makes them efficient flyers compared to bats, the birds are far from being perfect little “flying machines.”
Increased Energy Consumption
The researchers found that European pied flycatchers (and probably all other small birds as well) tilt their bodies backward when flying at low speed. When the bird lowers its tail, and raises its head, this leads to increased energy consumption.
“The technique increases the force generated by the wings — as when airplanes go in for a landing. For birds, which don’t have any engines, tilting the body is also about having the resulting force point in the right direction. This results in more body resistance and increased energy consumption,” says Johansson.