Wings on Their Fingers 



Despite 50 million years of evolution, bats don't become expert fliers overnight 



by Rick A. Adams and Scott C. Pedersen 



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As the sun sets, we approach the exit 

 hole of a maternity colony of little brown 

 bats {Myotis lucifugus) that has taken up 

 residence in the historic armory at Fort 

 Laramie, Wyoming. This colony contains 

 only females and young; the males gather 

 in bachelor colonies several miles away. A 

 few feet from the hole in the building's 

 wall, we block the bats' exit path with our 

 harp trap, a large metal frame vertically 

 strung with more than two hundred wires 

 spaced an inch apart. 



At dusk,^ several adult bats leave the 

 colony to begin their nightly insect hunt. 

 The first flies toward the trap, stops in 

 midair, hovers, deftly backs away, and es- 

 capes capture. A second adult quickly 

 folds up into a cannonball, barrels force- 

 fully between the wires, then flies away on 

 the wind. Another shps through sideways, 

 its wings perpendicular to the ground. 

 Barely tapping the wires, it leaves us 

 amazed at its split-second timing and acro- 

 batic skills. 



Moments later, a juvenile exiting the 

 colony awkwardly attempts an evasive 

 maneuver, but hits the trap and drops gen- 

 tly into a capture sack below. In quick suc- 

 cession, several other juveniles tumble out 

 of the exit hole, only to join their clumsy 

 comrade in the sack. Within a few min- 

 utes, we have bagged a dozen surprised, 

 but unharmed, juvenile little brown bats. 



Bats, the only true flying mammals, are 

 thought to have evolved more than 50 mil- 

 lion years ago, during the Eocene period, 

 from an insectivorous ancestor related to 

 moles and shrews. Anatomists have 

 known for at least three hundred years that 

 a bat's wing contains finger bones of the 

 same form, number, and relative position 

 as those of the human hand. The scientific 

 name for this mammalian order is Chi- 

 roptera (hand-wing), implying that the 

 bat's wing differs from other mammals' 

 forelimbs only in shape and proportion. 

 Indeed, each wing is composed of an elon- 

 gated forearm and, except for the thumb, 

 extremely long fingers sandwiched be- 

 tween two thin sheets of skin. The diminu- 

 tive thumb is left free. Elastic webbmg 

 connects the fingers to one another and 



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