304 IT. S. NATIONAL MUSEUM BULLETIN 217 



Rocky Mountains in an area separated from Alaska by extensive and 

 high mountains. I suspect that those nesting in Alaska winter there, 

 but since its winter climate is very diverse and its terrain is separated 

 by massive mountains into regions with distinct conditions, the origin 

 of migrants in such diverse regions can be a cause of variation in their 

 migratory schedules. 



Umer's (Urner and Storer, 1949) long records of the migratory 

 flights of plovers and sandpipers along the coast of New Jersey show 

 the duration of migration in that locality. From their reported rec- 

 ords between 1928 and 1938, I have extracted the dates during which 

 were observed principal migratory flights of some species also familiar 

 at Anaktuvuk. 







Duration in days 





Inclusive dates of flights in 



New Anak- 





New Jersey 



Jersey tuvuk 



Charadrius semipalmata 



May 4-June 4 



31 20 



Totanus flavipes 



April 24-June 13 



50 8 



Erolia minutilla 



April 29-May 30 



31 12 



Ereunetes pusillus 



May 7-June 7 



31 9 



It is apparent that in New Jersey the birds of these species are 

 migrating toward nesting in localities variously distant northward, 

 and that the samples are from populations known to be heterogeneous 

 in regard to nesting area. The shorter migration waves at Anaktuvuk 

 are produced by populations which are alike in nesting within Arctic 

 Alaska. Heterogeneity of migratory populations in regard to either 

 nesting or wintering areas may prolong the migratory passage over 

 any locality. In fact it seems likely that diversity of either back- 

 ground or future events might reduce the synchrony of migratory 

 action. 



Eegardless of the explanation for the diversity in the duration of 

 their migratory flights, it is apparent that the birds of no single 

 species arrive synchronously at Anaktuvuk. Let us consider the im- 

 plications in the lack of synchrony of Baird's sandpipers which con- 

 tinue to arrive for about 12 days. If they had traveled at the rate 

 of 60 miles a day during the 12 days preceding their arrival the popu- 

 lation would have been spread out along a course 720 miles long. 

 It is immaterial how closely this assumption fits the progress of migra- 

 tion in its northern course, for in relation to the range of sight of birds 

 the migrating elements of either flocks or individuals would be scat- 

 tered beyond range of communication with the remainder of the 

 population most of the time. I cannot imagine by what sense small 

 migrant birds could communicate in order to bring about coherent 

 action when spread over the time and distance in which each species 

 appears to be distributed during migration. In terms of proximity 

 of individuals relative to the range of sensory communication, the 



