450 S. F. MacLean, Jr. 



Prionocera gracilistyla, and Pedicia hannai (Holmes and Pitelka 1968, 

 Custer and Pitelka 1978). T. carinifrons, alone, makes up between 40 

 and 72% of the diet of adult longspurs between 10 June and 20 July 

 (Custer and Pitelka 1978), and over 50*^0 of the food fed to nestlings 

 (Seastedt and MacLean 1979). Overall, about 40% of the longspur diet 

 consists of T. carinifrons. Dunlin are almost entirely dependent upon T. 

 carinifrons (Holmes 1966), and both Baird's and pectoral sandpipers 

 feed largely upon larvae of this cranefly in June. Pectoral sandpipers 

 feed more in lowland meadows, and consequently take more larvae of 

 Pedicia hannai and Prionocera gracilistyla than do the other sandpiper 

 species. Semipalmated sandpipers differ from the other sandpipers in 

 specializing upon the smaller larvae of Chironomidae throughout the 

 season. Overlap in diet between species is greatest in early June, when 

 feeding sites are limited, and in mid- to late-July, when food is maxi- 

 mally available (Holmes and Pitelka 1968, Custer and Pitelka 1978). 



Density and Reproductive Success 



Both density and breeding success of these birds differ between 

 years and between areas of the coastal tundra, with at least part of the 

 variation due to differences in food supply. Average nesting density of 

 the five wader species varied from 0.09 nest ha"' in the pectoral sandpiper 

 to 0.18 nest ha"' in Baird's sandpiper (Table 11-11); however, these aver- 

 age values obscure both yearly and spatial variation. Baird's and semi- 

 palmated sandpipers occurred abundantly in census plots adjacent to 

 coastal lagoons; dunlin and pectoral sandpipers were scarce or absent 

 from these areas. Pectoral sandpipers are particularly variable in nesting 

 density from year to year. Holmes (1966) found from to 27 nests in a 

 40-ha study plot censused each season from 1960 to 1963. Average den- 

 sity varied between 0.02 and 0.20 nest ha"' in the four years (1969-1972) 

 included in this analysis. In contrast, nesting density of dunlin is more 

 stable, varying from 0.07 to 0.14 nest ha'' between 1968 and 1972 (Nor- 

 ton 1974). Pitelka et al. (1974) argued that some of the sandpipers, not- 

 ably the pectoral sandpiper, have an "opportunistic" social system that 

 allows maximum reproduction in favorable years and places; others, 

 such as the dunlin, use a more "conservative" social system that pro- 

 vides for a modest level of reproduction in all years. 



The waders are determinate layers. The vast majority of nests con- 

 tain four eggs, with some tendency for clutches laid very late in the sea- 

 son (usually replacement clutches) to be smaller. Hatching success varied 

 considerably between species, from 49% in Baird's sandpiper to 75% in 

 dunlin (Table 11-11). Most egg loss was caused by predation from jaegers 

 and least weasels. Baird's sandpipers, which suffer the greatest losses. 



