82 THE MIGRATIONS OF BIRDS 



Among northern shore-birds the earliest arrivals in 

 autumn are quite likely to be females, who press 

 southward immediately when eggs have been de- 

 posited. I have suspected that these early migrants 

 may be those whose nests have been destroyed in 

 some way, though certain observations hint that a 

 number of shore-birds share in part at least the habits 

 of phalaropeSj a group in which the female leaves the 

 care of eggs and young wholly to the male. 



Where there is segregation of the sexes, the young 

 often accompany the female. In fact, we may ex- 

 plain the flockings of such ducks as mallards if we 

 consider that the autumn flocks of males are mainly 

 the old drakes that have remained banded together 

 since the breeding season, while the mixed flocks of 

 early fall are females accompanied by young of both 

 sexes. 



When young are grown, in many cases the parents 

 drive them away to avoid their ceaseless calls for 

 food, and so force them to shift for themselves. 

 Many times bands of juvenile individuals are built 

 up, which must retain some coherence in subsequent 

 migrations. In Alaska, in August, I have found 

 young Alaskan longspurs banding in flocks in the 

 vegetation back of the beaches, with hardly any 

 adults among them. Young cowbirds may forsake 

 their foster parents to flock together in bands that 

 travel south in company, though perhaps joining 



