While it might be easy to imagine that the more crowded a bird flock becomes, the slower the whole process must also become, the opposite turns out to be true. For the first time, it's been proven that the bigger a bird flock becomes, the faster the birds that comprise it will fly.
The discovery comes thanks to scientists from Sweden's Lund University, who took a look at the flight speed of birds in an effort to determine which factors influenced how fast they would fly.
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Most of the findings didn't surprise the researchers. Expected items such as a bird's own aerodynamic properties (its weight and its wing shape), wind speed and direction, and the purpose of the flight (local food gathering vs. long trips) all indeed were factors influencing flight speed.
But the scientists observed that the size of the flock had a strong bearing on flight speed, which was not expected.
"I was surprised that it is such an important factor. It has usually been neglected in studies of bird flight," said study co-author Anders Hedenström in a statement.
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Hedenström and fellow author Susanne Åkesson collected their data on Sweden's Öland Island. There they studied birds' physical characteristics, counted flock populations, and recorded their speeds during flight.
To derive the birds' in-flight speed, they used an ornithodolite, a device a bit like a telescope with a laser rangefinder that can also capture key properties of wind, including speed and direction.
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No matter the species of bird (the pair studied five tern species of similar body dimensions), the duo's results showed that bigger flocks flew faster.
Why that's the case is the next question they hope to answer.
Among the theories, said the researchers, is that large flocks tend to be comprised of larger-sized birds, which move at faster speeds than smaller birds. Such flocks have an easier time taking full advantage of the turbulence behind other birds – particularly true for formation fliers such as geese. The turbulence lets them maintain higher speeds.
Hedenström's and Åkesson's findings have been published in the journal Philosophical Transactions of the Royal Society B.
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