WHITE-WINGED JUNCO 1023 



sawmill, where nesting was apparently successful despite the bustle of 

 human activity. 



In the summer of 1956 I found a nest built into a depression in the 

 groimd under a projecting slab of limestone. The nest construction 

 was an outer framework of coarse grasses and an inner lining of fine 

 grasses. Of the five nests I found in 1958, one was under projecting 

 limestone, two were under the root network of grass or shrubs, and two 

 were in small niches in limestone cliffs. Measurements of these nests 

 showed the following variations: outside diameter-10.0 to 15.0 centi- 

 meters; inside diameter-6.0 to 9.0 centimeters; inside depth-3.0 to 5.0 

 centimeters. The nest studied in 1959 contained 9.0 grams of nesting 

 materials (diy weight). 



Summarizing the above observations, I think that white-winged 

 j uncos usually select a cave-like situation, with a roof not far above the 

 nest. Exceptions are known, but do not seem to negate the rule. 



Eggs. — The white- winged junco usually lays three or four slightly 

 glossy ovate eggs. They are white or creamy white, speclded and 

 spotted with "auburn," "Brussels brown," "hazel," "sayal brown," 

 or "cinnamon brown," with undermarkings of "pale mouse gray." In 

 most cases the rather fine markings are concentrated toward the large 

 end, although some may have them well scattered. There is alwaj^s 

 a considerable amount of ground showing, and the spottings are often 

 somewhat dull and weak. The measurements of 30 eggs average 

 20.1 by 15.4 millimeters; the eggs showing the four extremes measure 

 ei.7 by 15.2, 20.6 by 15.6, and 17.8 by 14.7 milluneters. 



Incubation. — Acti\aties observed at a nest in Palmer Gulch in the 

 central Black Hills, elevation 5,000 feet, in June 1959, were as follows: 



June 2 — parents carrying nesting materials 



June 4 — nest lining completed 



June 6 — one egg in the nest 



June 7 — two eggs in the nest, both of which I marked with ink 



June 11 — four eggs in the nest 



June 20 — four eggs still present in the nest at 4 :00 p.m. 



June 21 — one young hatched before noon 



June 22 — four young in the nest at 9:30 a.m. 



July 2 — two young still in the nest, one on the ground beside it 

 From the above observations, one egg proved to have been in the 

 the nest for 15 days between laying and hatching, and all four eggs 

 were known to be under incubation for a minimum of 10 days. A 

 reasonable assumption is that one egg was laid each day, and that 

 incubation began on June 9, immediately after the fourth egg was 

 laid. Another assumption which cannot be proved is that all four 

 3"oung hatched on June 21. If these two assumptions are correct, 

 the incubation period is 12 days. Intensive observations of the crit- 



646-737— 68— pt. 2 28 



