HOMEWARD MIGRATION 



their nesting ranges before the first week in June. Robert H. Smith, who has 

 made extensive studies of breeding waterfowl in the north, tells me that 

 Pintails using the delta of the Mackenzie River do not begin nesting there 

 until early June, fully six weeks after the first Delta Pintails have their eggs 

 and at a time when a few of the earliest Delta hens have half-grown young. 

 Some of these Arctic ducks may winter with or near Manitoba Pintails ; per- 

 haps the two start north at about the same time. But some Delta individuals 

 are nearly finished with their reproductive activity before the northernmost 

 birds have started nesting. This same thing, of course, occurs with other 

 kinds of waterfowl: Arctic breeders are still migrating long after southern 

 relatives have produced you ig. 



The force that impels them to move northward must be the same for 

 Delta and Arctic Pintails, but the later stages of the sexual cycle are delayed 

 in the most northern individuals. Wolf son (1942:262), who studied the 

 breeding cycle and migratory behavior of the Oregon Junco, found that resi- 

 dent and migrant birds "differ in their gonadial cycles, although they flock 

 together in the winter and are subjected to the same environmental condi- 

 tions." These differences were between races or subspecies of the Junco; the 

 migrants may be distinguished taxonomically from the residents. In Pintail, 

 of course, Delta and Mackenzie River birds are not racially different. Be- 

 cause of the hen's fidelity to her home of previous experience, the schedule 

 of the breeding cycle must be linked to the geographic location of home, Del- 

 ta Pintails nesting in April and those of the Far North in June. The existence 

 of innate differences in breeding time is unlikely, because of the blending of 

 geographical units of population on the wintering grounds, where a Delta 

 drake might take a Mackenzie River hen for his mate. This mixing of blood 

 no doubt accounts for the absence of geographical races in the American 

 Pintail, and is the reason why a variation in time of nesting would not de- 

 velop as an inborn character in different units of the population. In other 

 words, the progeny of a June-nesting Mackenzie River Pintail would prob- 

 ably nest in April in Manitoba if artificially transported there as downy 

 young. In the Blue and Lesser Snow Geese we find this very thing happen- 

 ing. Captive geese taken from the wild are nesting at Island Park, Portage 

 la Prairie, in May, before their free wild brethren have reached the nesting 

 grounds in the Arctic. 



Sowls found the female to be faithful to her breeding place as long as 

 that area remained favorable for nesting. When, as sometimes happens, a 

 duck returns to find her homeland unfit for nesting — as when cover is lost 



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