AsianScientist (Oct. 27, 2016) – A decades-long study tracking flying birds reveals that body size and flight styles determine the scale of the birds’ migration, as predicted by the aerodynamic theory of bird flight. Details were published in Ecology Letters.
According to the study author Dr. Yuuki Watanabe, associate professor at the National Institute of Polar Research, Japan, billions of birds migrate every year to exploit seasonally available resources. The ranges of migration vary greatly among species, but the underlying mechanisms are poorly understood. In his paper, Watanabe hypothesized that flight mode—flapping or soaring—and body mass affects migration range through their influence on flight energetics.
To test this hypothesis, Watanabe compiled the migratory tracks of 196 species of flying birds recorded by electronic tags over the last few decades. He then demonstrated that the complex migration patterns could be explained by a simple energetic theory.
Increased energy consumption of larger flapping birds, such as cranes, geese, and swans that migrate between Japan and Siberia or travel similar distances in other parts of the world, limits their migration to shorter distances. In contrast, migration ranges of soaring birds, illustrated by raptors, vultures, and albatrosses that migrate globally with minimal energy consumption, are larger than those of flapping birds and independent of body size.
In other words, Watanabe wrote, for flapping birds, migration ranges decreased with body mass, as predicted from rapidly increasing flight cost with increasing body mass. The species with higher aspect ratio and lower wing loading had larger migration ranges. On the other hand, in soaring birds, migration ranges were mass-independent and larger than those of flapping birds, reflecting their low flight costs irrespective of body mass.
The article can be found at: Watanabe (2016) Flight Mode Affects Allometry of Migration Range in Birds.
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Source: Research Organization of Information and Systems.
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