SINGING IN CHORUS 85 



singing that I have observed. Mr. Hudson, how- 

 ever, has recorded a wonderful occurrence of it in the 

 crested screamer of La Plata: "Travelling alone 

 one summer day, I came at noon to a lake on the 

 Pampas, called Kakel a sheet of water narrow 

 enough for one to see across. Chakars in countless 

 numbers were gathered along its shores ; but they 

 were all arranged in well-defined flocks, averaging 

 about five hundred birds in each flock. These 

 flocks seemed to extend all round the lake, and had 

 probably been driven by the drought from all the 

 plains around to this spot. Presently one flock 

 near me began singing, and continued their power- 

 ful chant for three or four minutes ; when they 

 ceased the next flock took up the strain, and after 

 it the next, and so on, until the notes of the flocks 

 on the opposite shore came floating strong and clear 

 across the water, then passed away, growing fainter 

 and fainter, until once more the sound approached 

 me, travelling round to my side again. The effect 

 was very curious, and I was astonished at the 

 orderly way in which each flock awaited its turn 

 after the first flock had given the signal ' (op. cit. 

 p. 227). 



