By Sid Perkins
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.
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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 Hedenström, 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.