376 U.S. NATIONAL MUSEUM BULLETIN 237 part i 



coarser bits of stem an inch or less in length, all closely woven together. 

 The cup sometimes includes traces of a variety of other materials: 

 ptarmigan and rosy finch feathers, rabbit and cony fur, elk and burro 

 hair, pieces of cloth, ravelings of burlap, and, in one nest, a section of 

 blasting fuse. One egg was found with cotton adhering to the shell. 

 Occasionally small sharp pebbles fall into the nest and dent the 

 fragile egg shells. 



Nest buildmg begins about June 20 or later, and the actual con- 

 struction of the nest does not take long. F. W. Miller (MS.) watched 

 a site that was vacant on July 12; on July 14 the nest was complete 

 except for the lining; by July 16 it had been finished and two eggs 

 laid. Three days later the set of five was complete and the female 

 was incubating. Niedrach told me that in his experience the 

 female builds the nest alone; he never saw a male bring material to it. 



Eggs. — The number of eggs in complete sets varies from three to 

 five. Several nests Niedrach studied in the Arapahoe Range 

 contained the smaller number, while of 13 nests F. W. Miller and 

 others watched on Mount Bross, 1 contained two eggs; 2, three eggs; 

 5, four eggs; and 5, five eggs. 



F. C Lincoln (1916) describes the eggs as "pure white, slightly 

 glossy, unmarked; ovate pyriform in shape; measurements in inches: — 

 .91 X .60; .95 X 63; .97 X 62." Other sets exammed by the writer 

 agree with this description, with slight variations in the measurements. 



The measurements of 50 eggs average 22.7 by 15.6 millimeters; 

 the eggs showing the four extremes measure 25.8 by 16.0; 25.1 by 

 16.5] 20.5 by 16.0; and 23.2 by U.8 millimeters. 



In his notes, F. W. Miller mentions indications of pigmentation on 

 one set of eggs he collected; but when they were blown for preserva- 

 tion, no trace of pigment could be seen. The shells are very thin 

 and fragile, and of the few sets that have been collected, a number 

 have been broken in the blowing or otherwise destroyed. 



According to the limited data available, eggs are laid at the rate 

 of one a day until the clutch is complete. The earliest date eggs 

 have been found is June 30, when a set of four was discovered on 

 Mount Bross. Fresh eggs have been found as late as July 19, which 

 were the second set of five laid in a nest from which the first set had 

 been collected on July 8. A nest completed on Arapahoe Peak, 

 Grand County, on July 28, contained three eggs on August 7, the 

 date the eggs were taken. 



Young. — According to Niedrach, incubation probably lasts from 

 12 to 14 days. The earliest hatching date noted is July 8; full clutches 

 of eggs still under mcubation have been found several times as late as 

 July 27. Incubation of second sets, when laid, probably continues 

 into early August. No exact temperatures of the air around the 



