Thursday, February 06, 2014

How bumblebees stay aloft at high altitudes

As altitude increases flight becomes much more difficult.  Air density gives less material to push against, and reduced oxygen concentrations make the exertions of flight that much more demanding. But there are rewards for going higher. Within the bees, there are fewer species at alpine altitudes, which can make these ecosystems less competitive than the lower ranges of mountains. Bumblebees, for instance, have been observed foraging as high as 5,000 meters above sea level; and some flies and butterflies live at up to 6,000 meters.
Stroke patterns of a bumblebee at 3,250m 
(green) and simulated 8,130m (blue). 
The lower- altitidue strokes are shown on 
both sides of the insect for comparison.
Source: Dillon and Dudley, Fig 2. 
But what is the upper limit of flight for a heavy insect such as a bumblebee? In a study in the February 2014 issue of Biology Letters, Dillon and Dudley tested the ability of bumblebees to get aloft in a plexiglass chamber with progressively reduced air pressure. One of their bees was still able to fly at the equivalent of 9.000 meters, which would be higher than Mt. Everest!
Dillon and Dudley analyzed film of the bees to figure out how they stayed aloft.. They found that the bees extended the range of their strokes. This is as opposed to increasing the rate of beating, which is the strategy for example used by water polo players to lift themselves out of the water. Dillon and Dudley do not speculate why the bees follow this strategy.
As for the significance of the extra capacity, they note that their test only asked that the insects get airborne. In the wild, the bees might need this ability to fly higher, or to maneuver while loaded, to evade predators.

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