316 



U. S. NATIONAL MUSEUM BULLETIN 217 



19 migratory species nesting principally or exclusively in northern 

 Alaska (table 9, p. 266) are of many families and vary in weight from 

 10 to 2500 grams. Some winter below the equator in South Ameri- 

 ca, on the shores of the Pacific Ocean, or in the continent of Asia. 

 They have few common characters except their habitual convergence 

 on the same arctic nesting area. The family Scolopacidae is most 

 numerously represented among these arctic-nesting birds, but 12 

 other families are also represented at Anaktuvuk by one or more 

 species. Among the 80 migratory species arriving to nest at or north 

 of Anaktuvuk, the 34 listed below nest only in the Subarctic or in the 

 Arctic, and of these species, the 18 marked with an asterisk (*) breed 

 solely in the Arctic. 



*Gavia adamsii 



Olor columbianus 

 *Branta canadensis taverneri 

 *Branta nigricans 

 *Anser albifrons frontalis 

 *Chen hyperborea 



Clangula hyemalis 



Grus canadensis 



Pluvialis dominica dominica 

 *Squatarola squatarola 

 *Numenius phaeopus budsonicus 



Heteroseelus incanum 

 *Erolia melanotos 

 *Erolia bairdii 



Erolia fuscicoUis 

 *Erolia alpina pacifiea 



Limnodromus scolopaceus 



♦Micropalama Mmantopus 

 Breunetes pusiUus 

 *Tryngites subrnflcollis 

 ♦Limosa lapponica 

 *Orocethia alba 

 Pbalaropus f ulicarius 

 *Stercorarius pomarinus 

 *Stercorarius parasiticus 

 *Stercorarius longicaudus 

 *Larus b3i)erboreus barrovianus 

 Sterna paradisaea 

 Sayornis saya yulionensis 

 Oenantbe oenantbe oenanthe 

 Pbylloscopus borealis kennicotti 

 Montacilla flava tschutschensis 

 Oalcarius lapponicus alascensis 

 Plectropbenax nivalis nivalis 



Size of Clutch 



There are many records of the numbers of eggs in the sets of 

 birds' eggs which have been assiduously collected, and if the collector 

 unobtrusively watched the nest until the last egg was laid and then 

 determined that no subsequent addition was made, the number taken 

 as a set represents the reproductive accomplishment of the female bird. 

 But if sustained observation of the nest is not recorded, there is a 

 chance that collection of the eggs preceded the completion of laying 

 or that accident or predation may have removed one or more of them. 

 This can introduce a statistical bias in any calculation, based on col- 

 lected sets, of the normal number of eggs laid in a clutch. 



In order to illustrate data available from collections by experienced 

 naturalists, I have listed below the number of eggs in sets taken by 

 Murdoch and his associates at Barrow during their expedition for 

 observation of the First International Polar Year 1882-1884, and in 



