1342 U.S. NATIONAL MUSEUM BULLETIN 237 paet 3 



The eggs are laid from late May through early August. William 

 L. Dawson (1923) states that this race may raise one or two broods. 

 I have found no records, however, of a pair with young out of the 

 nest and with a second nest of eggs or young such as was the rule 

 in the Puget Sound sparrows at Friday Harbor. When all the avail- 

 able egg dates are arranged chronologically, they show no hint of a 

 gap in the series that would suggest a second brood. My observations 

 in 1960 provide one illustration of the wide variation between popu- 

 lations as to the time nesting may start. On June 19, 1960, my 

 husband and I found a pair of mountain white-crowned sparrows at 

 Tuolumne Meadows with young about four days old. If we assume 

 that the incubation period was the same length as in the Nuttall's 

 sparrow, the female would have laid the first egg of this clutch on 

 June 1. At King's Creek Meadows, on the other hand, the females 

 had not even arrived by June 26. Even assuming they came the 

 next day and began work on their nests at once, they could hardly 

 have started laying before June 29 at the very earliest, some four 

 weeks later than the pair at Tuolumne Meadows. 



The average number of eggs per clutch for 164 clutches is 4.03. 

 If only those clutches of oriantha from localities within the same 

 latitudinal range as nuttalli are averaged, the mean is almost identi- 

 cal, — 4.04 for 145 clutches. This is significantly larger than the aver- 

 age clutch size for nuttalli (3.27 for 215 clutches). The number of 

 eggs per clutch in oriantha is usually four whereas in nuttalli it is 

 usually three. Percentages for oriantha are as follows: 3 eggs 5.0 

 percent; 4 eggs 87.6 percent; 5 eggs 6.8 percent; 6 eggs (one record 

 only) 0.6 percent. Two extreme records of two and seven eggs each 

 were not included in the averages; it is not certain that the set of 

 two was complete and we have no evidence that the clutch of seven 

 was laid by a single female. 



As clutch size varies with month of laying in nuttalli, I calculated 

 the average clutch size for oriantha for June and July separately: for 

 June 122 oriantha sets average 4.08 eggs per clutch, 21 nuttalli sets 

 average 3.24; for July 37 oriantha clutches average 3.89 eggs per 

 clutch, 7 nuttalli sets average 3.14 per set. 



These comparisons show that some factor or factors other than 

 latitude and month of laying must be responsible for the difference in 

 average clutch size between oriantha and nuttalli. The most obvious 

 environmental difference is that of altitude and the resulting differ- 

 ences in the climates of the breeding grounds. A scatter diagram we 

 constructed of the number of recorded oriantha eggs per clutch in 

 relation to elevation, which ranges from 4,000 feet to 11,000 feet, 

 shows no obvious correlation, either positive or negative, with altitude. 



