Music and Dancing in Nature. 283 



the whole flock mad. There are also species that 

 always live in pairs, like the scissors-tails already 

 mentioned, that periodically assemble in numbers 

 for the purpose of display. The crested screamer, 

 a very large bird, may also be mentioned : male and 

 female sing somewhat harmoniously together, with 

 voices of almost unparalleled power : but these 

 birds also congregate in large numbers, and a 

 thousand couples, or even several thousands, may 

 be assembled together : and, at intervals, both by 

 day and night, all sing in concert, their combined 

 voices producing a thunderous melody which seems 

 to shake the earth. As a rule, however, birds that 

 live always in pairs do not assemble for the purpose 

 of display, but the joyous instinct is expressed by 

 duet-like performances between male and female 

 Thus, in the three South American Passerine 

 families, the tyrant-birds, wood-hewers, and ant- 

 thrushes, numbering together between eight and 

 nine hundred species, a very large majority appear 

 to have displays of this description. 



In my own experience, in cases where the male 

 and female together, or assembled with others, 

 take equal parts in the set displays, the sexes are 

 similar, or differ little ; but where the female takes 

 no part in the displays the superiority of the male 

 in brightness of colour is very marked. One or two 

 instances bearing on this point may be given. 



A scarlet-breasted troupial of La Plata perches 

 conspicuously on a tall plant in a field, and at inter- 

 vals soars up vertically, singing, and, at the highest 

 ascending point, flight and song end in a kind of 

 aerial somersault and vocal flourish at the same 



