912 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 2 



bottom) with horsehair. In the swale habitat, as in the old riparian 

 habitat, the shell is made of coarse grasses (sometimes mixed with 

 weeds), chiefly the stems but including leaves and the fine stalks of 

 inflorescences. Elsewhere the outer shell is built of similar material 

 (much of it is not grass) — weed-stems, at times with the top of the 

 root or with what seem to be strips of some thin, gray plant cortex 

 such as fine bark. Except for this last and the leaf-blades, most of 

 this outer material is largely from }^ to 1 millimeter thick, and more 

 often below than above these limits. The use of a fine thorny twig 

 (Acacia constricta?) seems unusual in the swale habitat, though twigs 

 are the common component of nests in farmland habitat. A con- 

 spicuous component at times, because it is easily identifiable, is the 

 stalk of an Eriogonum. 



Over-all outside dimensions of the shell are usually 8.5 to 12 centi- 

 meters in diameter, and 6 to 8 centimeters in depth; sometimes larger 

 in nests of tobosa grass (swale habitat), or with grasses stragghng 

 beneath. The inner cup is usuaUy 4 to 5.5 centimeters in diameter 

 and 5 to 6.5 centimeters deep. C. E. Bendire (1882) describes the 

 nest in the old riparian habitat as "tkree inches [7.5 centimeters] deep 

 in the inside, so deep in fact that nothing but the tip of the tail of the 

 bird is visible when setting." 



Eggs. — The set usually comprises four eggs. Recent extremes show 

 a bird incubating two eggs, May 1958 (Marshall, MS.), and a nest 

 with five fresh eggs (one a cowbird's) taken on Aug. 8, 1959 (Patrick J. 

 Gould), both in farmland habitat. But in C E. Bendke's time, sets 

 of five were not unusual, and three eggs were rare or unknown. The 

 eggs are sHghtly glossy, ovate, very pale bluish w^hite, and unmarked. 

 W. G. F. Harris' measurements of 50 eggs average 19.1 by 13.9 

 millimeters; the eggs showing the four extremes measure 20.3 by 14.7, 

 18.8 by 15.0, 17.8 by 14.0, and 18.8 by IS.O milHmeters. C. E. 

 Bendire (1882) gives somewhat larger figures, while my own attemj)ts 

 give smaUer ones; doubtless this reflects differences in individual 

 techniques and measuring equipment. 



Incubation. — The female is a close sitter, even when the eggs are 

 fresh. One whose eggs were hatching on September 1 refused to fly 

 when I was less than a meter away. The male on such occasions of 

 danger seems usuaUy to be singing near by. One bu'd in the desert 

 wash habitat came onto the nest so secretively that I never saw her, 

 though I was watching for her, until she w^as incubating. While I 

 have never captured incubating birds, I have no reason to suppose 

 that males incubate. The length of the incubation period is unknown. 



Young. — A young bkd I thought to be newly hatched on May 17, 

 1958, had sparse dark down. Young seem to remain in the nest 9 or 

 10 days. A nest found with two eggs and two newly hatched but 

 dry young on Sept. 1, 1939, was empty on September 12, but two of 

 the four young were caught and banded near by. This nest was also 



