Magazine article Science News

Invisible Trail: Analyzing the Vortices in the Wake of a Bat

Magazine article Science News

Invisible Trail: Analyzing the Vortices in the Wake of a Bat

Article excerpt

Experiments that reveal the swirling air around a flying bat indicate that those mammals generate lift and thrust with their wings much differently than birds do.

At first glance, birds and bats seem to move through the air in similar fashion. However, aerodynamic details of the two groups' flapping techniques, particularly at low flying speeds, are quite different, says Anders Hedenstr6m, a biomechanicist at Lund University in Sweden. On the upstroke, a bird can separate the large feathers on its wings, permitting air to flow cleanly through and minimizing any downward, altitude-robbing force. Bats can't do that, he notes, because their wings are continuous, although flexible, membranes.

Hedenstrom and his colleagues studied the flight techniques of Glossaphaga soricina, a 5-centimeter-long, nectar-feeding bat that ranges from Mexico to northern Argentina. The team used a wind tunnel similar to the tunnels employed by engineers to evaluate scale models of aircraft. During the experiments, the bats drank a sweet solution from a tube dangling in front of cameras as they hovered facing a headwind.

Laser pulses illuminated tiny liquid droplets delivered into the airflow and enabled the researchers to calculate the strength and rotation of the eddies that the bats' flapping wings created, says Hedenstr6m. The researchers describe their findings in the May 11 Science.

When flying at slow speeds, about 1. …

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