448 



S. F. MacLean, Jr. 



pipers may have evolved to allow them to exploit the abundance of prey 

 in lowland meadows while maintaining hatching at the optimal time of 

 the season. 



Use of Habitats and Food Habits 



The bird species differ in their distribution over major habitat units 

 (Figure 11-9) and their use of microhabitats within these (MacLean 1969, 

 Custer 1974); however, there is considerable overlap in both habitat use 

 and prey selection throughout the breeding season (Holmes and Pitelka 

 1968). Early in the season the birds make greatest use of upland habitats, 

 with only pectoral sandpipers and red phalaropes making significant use 

 of wet meadow and pond habitats. Longspurs feed mainly on seeds dur- 

 ing the first ten days of June, and thus differ from the waders, but switch 

 to larval Diptera once breeding commences (Custer and Pitelka 1978). 

 All birds seem to feed preferentially along the edge of retreating snow- 

 fields, suggesting that insects just exposed are more easily located or cap- 

 tured than those that have achieved full activity in thawed tundra. 



Territorial defense diminishes during incubation, and defense of the 

 breeding territory ceases altogether when the young leave the nest in early 

 July. The adults commonly lead the young from upland nesting habitats, 

 which provide relatively little cover, to low-lying meadows, where vege- 

 tation provides greater cover from predators. It is unlikely that abun- 

 dance of food is a serious factor influencing habitat choice at this time. 

 Since emergence of adult insects is sensitive to weather, periods of food 



Boird's sandpiper 

 Loplond longspur 



dunlin 



semipalmated sandpiper 



Well-drained Ter- ♦ ^ 



races and High-centered pectoral sandpiper^ 



Stream Banks Polygons 



Beoch 

 Ridges 



red pholarope 



Mesic 

 Meadows Low-centered y^g^ 



Polygons Meodows 



Ponds 



3,5,6 



1.2 



/. Carex-Oncophorus meadow. 



2. Wet Dupontia meadow. 



3. Polygon trough. 



4. Moist Dupontia meadow. 



5. Basin of low-centered polygon. 



6. Rim of low-centered polygon. 



7. Carex-Poa mesic meadow. 



8. High-centered polygon. 



FIGURE 11-9. The distribution of preferred breeding hab- 

 itat of birds along a mesotopographic gradient. 



n 



