322 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



from foliage rather than taking it in flight. Natterer's is fairly im- 

 partial, but the whiskered very rarely captures a flying insect, pre- 

 ferring to search the hedgerows and fences, especially for spiders, 

 of which it is inordinately fond. Both species have a well-developed 

 tragus, and in both, but more particularly in Natterer's, there is a 

 marked development of the glandular pads on the face. 



How bats find their prey is a mystery that has not yet been solved. 

 It is certain that they cannot find it by sight, and there does not seem 

 to be any evidence that their powers of scent are particularly acute. 

 Plow, then, does the noctule {Nyctalus noctula), flying high and fast, 

 find its prey ? If you throw a pebble into the air beneath a hawking 

 noctule, the bat will dive on to it, swerving away from it at the very 

 last moment without touching it. Attach a fly to a long line and 

 make casts into the air while bats are hawking and you will have 

 them diving at the fly, but it is very unlikely that you will catch one. 

 Daubenton's bat {Myotis dauhentonii) is sometimes caught on the 

 flies of anglers, but almost always by the wing. I do not think that 

 there has been a single instance of the bat being caught by the mouth, 

 which suggests that at the last moment (but too late to avoid con- 

 tact altogether) it has realized its mistake. All this suggests that 

 the supersonic squeak sends back an echo from anything flying into 

 or across the path, but it does not explain how the bat knows that 

 that something is worth investigating. Yet I have never seen one 

 bat dive at another, even when there have been many flying at random 

 in a confined area. Nor does it explain how the long-eared and the 

 whiskered know that there is an insect or a spider on what their 

 echo-location must have told them is an obstacle to avoid. Yet in a 

 long experience of whiskered bats, I have not seen one hit a fence or 

 make fruitless visits along a hedge. 



One would be inclined to say that the supersonic tone was even more 

 selective than we know it to be were it not for certain things that 

 field experience has brought to notice. I have seen bats of different 

 species collide in mid-air — on one occasion a noctule with a serotine 

 (and both animals were killed), and on another occasion a pipi- 

 strelle with a barbastelle (when the pipistrelle was killed). These 

 accidents happened during the evening hawking, and one can only 

 suppose that at the time echo-location had stopped, possibly because 

 both animals had captured insects and their mouths were closed. 



Field experience shows too that there are times when echo-location 

 does not function at all. I have caught many bats by netting their 

 dens of a summer night. At bne time, anxious to discover whether 

 bats flew at night or not — it was at that time thought that they had an 

 evening and a morning flight only — I made a number of all-night 

 watches at dens of noctule, whiskered, pipistrelle, serotine, and Natter- 



