Scientists find nightingales’ optimal flying speed for long distances

By Stephen Beech

Nightingales manage their epic migrations by flying at a "medium" pace, according to a new study.

Researchers have pinpointed the speed that helps the migratory birds maintain "peak efficiency" during their transcontinental journeys.

They found that, at the end of the summer, when thrush nightingales leave Europe and head for southern Africa, they do not fly at full speed but instead maintain an "even" pace.

Migratory birds spend hundreds of hours in the air and up to now, scientists had assumed that the efficiency of converting energy into flight power was constant regardless of the speed.

But, using wind tunnel experiments involving nightingales, researchers in Sweden have shown that wasn't the case.

Pablo Macías Torres, a biology researcher at Lund University, said: “We have discovered that the nightingales are not equally efficient at all speeds.

"Their efficiency is highest at an intermediate flying speed - approximately seven to eight metres per second – thus neither at very low nor very high speeds."

Previous models suggested that birds convert around 23% of their metabolic energy – the energy the body releases from nutrients through the metabolic process – into flight.

The new results, published in the journal Current Biology, show that the maximum value is closer to 15%, and above all it depends on how fast the bird flies.

PhD candidate Torres said: “Our study shows that the energy efficiency varies and reaches a maximum at an intermediate speed – so all speeds are quite simply not equally efficient."

He says the results not only give the best estimates yet of birds’ flight energetics, but also help researchers to construct more exact models of bird flight and explain how small birds are able to make their transcontinental migrations.

Torres added: “Understanding birds’ flight efficiency helps us to assess the remarkable physiological adaptations that make it possible for birds to conquer the air and complete extraordinary long-distance flights, such as the nightingales’ impressive flight south."