SEGREGATION DURING MIGRATION 8i 



viduals. In a few species male and female seem to 

 arrive together and proceed at once to the business 

 of preparing a home. This is especially true of some 

 shore-birds, that go to the far northern tundras, 

 where mating may take place almost on the day of 

 arrival. 



In late summer, after the nesting season, males 

 frequently flock by themselves and remain in bands 

 until autumn. Yellow-headed blackbirds elect such 

 segregation, as do most of the surface feeding ducks, 

 in which males desert the females before the eggs are 

 hatched. Such bands tend to hold their coherence 

 until time for departure for the south, and so the 

 sexes may in part travel in separate bands. Especial 

 attention has been paid to ducks in this regard, and 

 it has been found that often males will pass in flight 

 at certain times to the exclusion of females; again 

 the flocks will mix, or bands of females will out- 

 number the males. Once they are near the winter 

 home, all this changes and the sexes intermingle. In 

 fact, some of the preliminaries of pairing, or actual 

 mating itself, are carried on in the south. Black 

 ducks are frequently found in pairs as early as Janu- 

 ary, with female leading and the male following as 

 they take flight, a certain indication that the birds 

 are paired. These paired individuals naturally mi- 

 grate north in spring together, though among other 

 ducks of the same species that are not mated the 

 sexes may fly separately. 



