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What determines the speed at which birds fly?
July 17, 2007Aerodynamic scaling rules that explain how flight varies according to weight and wing loading have been used to compare general speeds of a wide range of flyers, from the smallest insects to the largest aircraft. In a paper published this week in the open access journal PLoS Biology, Thomas Alerstam, Mikael Rosen, and colleagues from the University of Lund in Sweden analyze the flight speeds of 138 bird species and overturn the general assumption that maximum flight speed of a species is solely determined by such rules. Flight speed doesn't just depend on the size of the bird (mass and wing loading), but also reflects functional constraints and the evolutionary lineage of the species in question.
The authors argue that only empirical measurements of flight speeds enable you to evaluate how general such aerodynamic rules really are. They used tracking radar measurements of the cruising speeds of migrating birds (collected by themselves and others) to do the analysis and provide the comprehensive dataset with the paper (e.g. this contains the flight speed of approximately one-third of all European bird species). Their analysis reveals that the difference between the speed of small and large birds is not as great as expected; they suggest that this surprising result is likely to be the result of disadvantages associated with very slow speeds among smaller birds and with very fast speeds for larger birds. They also show that the evolutionary history of the species helps explain much of the variation in flight speed: species of the same group tend to fly at similar characteristic speeds. For example, birds of prey and herons had slow flight speeds, on average, given their mass and wing loading, whereas the average speed for songbirds and shorebirds was faster than would be predicted.
This study suggests that there are different functional adaptations affecting flight differently among different types of bird, and that there exists a diversity of cruising flight characteristics among birds that remain to be explored and understood.
Public Library of Science
Public Library of Science
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An articulated lorry was driven for a period of one year with a boat tail (of varying length) and one year without a boat tail. The improved aerodynamics, depending on the length of the boat tail, resulted in reduced fuel consumption (and emissions!) of up to 7.5 percent. The optimum boat tail length proved to be two metres.
Secrets of insect flight revealed
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Composites for energy
Advanced composite materials are playing a vital role in improved design and reduced operating costs for renewable energy technologies.
Trading energy for safety, bees extend legs to stay stable in wind
New research shows some bees brace themselves against wind and turbulence by extending their sturdy hind legs while flying.
We saw it coming: Asteroid monitored from outer space to ground impact
Reports by scientists of meteorites striking Earth in the past have resembled police reports of so many muggings - the offenders came out of nowhere and then disappeared into the crowd, making it difficult to get more than very basic facts.
Engineer devises ways to improve gas mileage
Last summer, it was very expensive to fill up a gas tank when the gasoline price hit close to four dollars a gallon. Transportation by road or air consumes fuel, which not only increases our vulnerability to foreign imports but also is a source of greenhouse gas emissions that will impact adverse change in climate and global warming.
March launch planned for ESA's gravity mission
ESA is now gearing up to return to Russia to oversee preparations for the launch of its GOCE satellite - now envisaged for launch on 16 March 2009.
The science of speed -- how world-class UK research is behind the fastest car in the world
World class UK research is helping to build the fastest car in the world thanks to the Engineering and Physical Sciences Research Council (EPSRC).
Denser computer chips possible with plasmonic lenses that 'fly'
Engineers at the University of California, Berkeley, are reporting a new way of creating computer chips that could revitalize optical lithography, a patterning technique that dominates modern integrated circuits manufacturing.
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