The Detritus-Based Trophic System 445 



ropes), four gulls (including two jaegers and the arctic tern), the snowy 

 owl, and three passerine species. Excluding the aquatic-feeding species, 

 the terrestrial bird fauna consists of a group of carnivores (pomarine and 

 parasitic jaegers, and snowy owl) that are conspicuous only in years 

 when lemmings are abundant, and alarge group of "insectivorous" birds. 



The paucity of passerine species and abundance of waders contrasts 

 sharply with temperate avifaunas. Of the three passerine species, the 

 snow bunting is limited by lack of natural nesting cavities to areas 

 around present or past human settlements, and the redpoll, a seed-eating 

 finch, occurs sporadically in both time and space. Thus, the Lapland 

 longspur is the only generally distributed passerine bird species of undis- 

 turbed tundra in the Barrow region. 



The dominance of waders over passerines is limited to the northern 

 Coastal Plain. Many more passerine species breed in the Foothills and 

 the Brooks Range. This argues for the importance of ecological rather 

 than biogeographic factors in limiting the diversity and composition of 

 the breeding bird fauna of the arctic coastal tundra. 



Studies on the birds of the Barrow area conducted for many years by 

 F. A. Pitelka and his associates provide a firm foundation of information 

 on natural history and breeding ecology. The present discussion will 

 focus upon six species: the dunlin, pectoral sandpiper, Baird's sandpiper, 

 semipalmated sandpiper, red phalarope and Lapland longspur. These six 

 species are the major consumers of arthropods in the coastal tundra eco- 

 system. They form a guild of avian consumers linked to the detritus- 

 based trophic system. 



Phenology 



The birds arrive on the tundra in early June, as the tundra is just be- 

 ginning to emerge from the winter snow cover, and daily mean tempera- 

 tures are still well below freezing. Establishment and defense of territor- 

 ies occurs as the snow melts; and courtship and nesting follow shortly. 

 The median date of clutch completion falls on or before 15 June in both 

 dunlin and Lapland longspurs (Table 11-11). On this date the tundra is 

 normally about SO'Vo snow covered (Chapter 2), and much of the exposed 

 habitat is unavailable to feeding birds because of ponded meltwater. 

 Breeding of other species follows shortly, with median dates of clutch 

 completion falling within a two-week period. Except for the phalaropes, 

 which are semi-aquatic, the early onset of egg-laying concentrates early 

 season activities in areas of upland tundra. 



Nesting synchrony within species is high. Custer and Pitelka (1977) 

 found that the median date of egg-laying fell between 7 and 14 June, and 

 followed the first by an average of only seven days in Lapland longspurs 



