RESIDENCE IN THE ARCTIC 305 



migratory process is not concerted but widely distributed. It seems 

 as if individuals and groups, but not the populations as units, guide 

 the migration. 



Progress Toward Laying 



Judging from the size of testes, males of most species are ready for 

 breeding at the end of migration, although Alaska longspurs with 

 small testes were taken during the first 10 days in which migrants 

 were arriving. However, readiness for reproduction does not termi- 

 nate migration and start settled residence on the breeding ground, 

 for immature individuals of some species migrate to summer near 

 the breeding grounds. 



Mallards, mergansers, golden plover, and birds of several other 

 species commonly appear on the nesting grounds in pairs. On the 

 other hand, some flights of arriving sandpipers are composed prin- 

 cipally of males, and the males of some passeriform species take up 

 nesting territories before females are seen. The variety of physio- 

 logical phases and behavior of arriving migrants is interesting, but 

 no common sequence can be derived from it to mark the conditions 

 which transform a migrating bird into a settled bird with all its in- 

 terest focused upon mating and preparations for subsequent nesting. 

 From my general impression of their behavior, I would have said that 

 pintails ducks and all earlier arriving migrants took the transition 

 from the migratory to breeding state in more leisurely fashion than 

 did later migrants, yet an examination of my records gives no sug- 

 gestion that the interval between arrival and laying is related to 

 earliness of arrival. 



The recorded arrival period of migrants of nesting species lasted 

 from 2 to 32 days. I think that more migrants arrived to settle during 

 the first half of the period of each species than arrived later. Some 

 later migrants appeared in haste to move northward and those which 

 settled found less free territory. The period from midmigration to 

 the middle of tlie week after nesting begins is a fair measure, for 

 most of the species at Anaktuvuk, of the time elapsed between ar- 

 rival and laying. This elapsed time is estimated for 24 species in 

 table 13. The interval is 4 days for 2 species, 5 to 9 days for 4, 10 to 

 19 days for 16, and 20 to 23 days for 2 species. These estimates in- 

 dicate that the interval between arrival and laying differs among 

 species and that for a few species it is less than a week. In temperate 

 climates some early nestmg pairs of many species lay as soon after 

 arrival as do the arctic birds. Mrs. Oakeson (1954) shows that at 

 Momitain Village, Alaska, for Gambel's sparrow the interval between 

 the average arrival date and first laying was about 8 days. The earli- 

 est nesting birds of the race of white-crowned sparrows {Zonotrichia 



