igS THE SOCIAL LIFE OF ANIMALS 



slower dowitchers took the chord of the arc made 

 by the wheeling flock and so caught up with and 

 again became an integral part of the flying group. 

 Soon again the slow dowitchers lagged and the whole 

 performance was repeated. 



These observations do not reveal the stimulus 

 which releases the wheeling mechanism of the main 

 flock. The simplest explanation, that the leader, find- 

 ing himself out alone in front, starts to turn and 

 so gives a stimulus to the keen-sighted remainder so 

 that they also shift direction almost instantaneously, 

 does not hold in this mixed flock, for the observa- 

 tions indicate clearly that the apparent leader, the 

 golden plover, was following along in front of the 

 main flock as much as the slow dowitchers were fol- 

 lowing along behind it. 



Neither does this simple-leadership sort of ex- 

 planation fit the facts as observed among wheeling 

 flocks of other shore birds or of pigeons. In such 

 flocks the stimulus to turn frequently seems to 

 originate in one of the flanks, and spreads from that 

 point rapidly through the flock. Here again the ap- 

 parent leaders may not be the actual ones. It is pos- 

 sible, though we are not yet sure of it, that in such 

 flocks made of birds which we cannot tell apart, the 

 faster individuals also may dive through the flock 



