13141 Grinnell: Mammals and Birds of the Colorado Valley 171 



what less than one month (in different individuals, March 9 to April 

 3). The prennptial molt in Spizella passerina arizonae involves in 

 both sexes and apparently all ages, only the capital tracts, and, per- 

 haps in only a few individuals, part of the pectoral region. This is 

 apparently the same condition of affairs found in Spizella passerina 

 passerina, of eastern North America, as described by Dwight (1900, 

 p. 199). 



Since there are in the Museum two skins (nos. 4160, 4161) taken 

 by J. G. Cooper at Fort Mohave. December 24, 1S60, it is evident that 

 the western chipping sparrow passes the winter in the Colorado Valley. 



Spizella breweri Cassin 

 Brewer Sparrow 



Since this sparrow was noted as early as February 19, when it 

 was common a few miles south of Needles, a fair inference is that it 

 is a winter sojourner in the region. At any rate, from the above date 

 on until the middle of April, scattering flocks were of frequent note 

 at all our collecting stations, on either side of the river, down to a 

 point on the California side four miles north of Potholes. Here several 

 individuals were seen April 23, the last for the season. As with the 

 chipping sparrow, with which the Brewer sparrow was not infrequently 

 associated, the latter occurred both on the desert uplands and along 

 the river bottom lands. The preferred feeding grounds were probably 

 on the desert, the river being visited only for water. 



The series of specimens of Spizella breweri secured (nos. 13201- 

 13226) shows that there is a partial prennptial molt, beginning (as 

 shown by no. 13219, a male) as early as March 11, and continuing at 

 least until March 27. This molt, however, is very limited in extent, 

 involving only the chin and throat in addition to replacement of a 

 part of the feathers of the crown, particularly anteriorly, and the chest. 

 There is a scarcely discernible change in color, resulting in slightly 

 whiter throat and clearer ash and clay color on the crown, certainly 

 not enough to warrant the molt from the standpoint of color signifi- 

 cance. Neither does the very small amount of wear which the speci- 

 mens in hand up to the first of March appear to have incurred, seem 

 sufficient to make a spring molt imperative. Yet the latter would 

 appear the best explanation, restricted area of replacement pointing 

 towards relative importance of the process. A spring molt may have 



