184 THE MIGRATIONS OF BIRDS 



whence their need of extensive marshes as hiding 

 places. Females follow the males to the seclusion 

 of the marshes when the young are old enough to 

 shift for themselves, but have their moult delayed 

 until late summer. This early separation of the 

 sexes persists in part through the autumn, though 

 mixed flocks of males and females are of frequent 

 occurrence. 



The duck population of the Bear River marshes 

 continues to grow steadily beyond the normal breed- 

 ing stock, until the first of September, with a sud- 

 den increase at the end of August, when hordes of 

 young begin to arrive from other breeding areas. 

 Between September i and 10 fully two thirds of the 

 ducks that have gathered migrate out to other 

 regions. Cinnamon teal and redheads leave in a 

 body at this time, and with them go many others. 

 The sudden disappearance of the host of birds is 

 easily noted, but others continue to arrive, and by 

 October i enormous numbers are present. During 

 the second week in October there is increase in flight 

 from the north, which continues steadily until the 

 close of the season. Ice closes the bays in part by 

 Thanksgiving time, and between December i and 

 15 the last of these birds are driven to other regions. 



Ducks that I banded at this point were killed 

 subsequently over the entire western United States, 

 from western Missouri and Kansas to California, 



