Vol. XXXI j SwARTH, California Forms of Psaltriparus. 503 



exposure during the year, so that various combinations result. 

 This species varies seasonally to a much greater extent than does 



P. plumbeus. 



The southern California series of bush-tits is the most extensive 

 one available, and there are enough specimens from this region to 

 illustrate the change in appearance during the year. Between 

 birds in the freshly acquired plumage of October, and those m the 

 frayed feathers of May and June, there is a vast difference. Se- 

 lected specimens at hand, representing almost every week of the 

 intervening period, laid out in chronological order, clearly illustrate 

 the nature of the change, and show that there is some alteration 

 in appearance from month to month almost throughout the year. 

 There are sufficient specimens of bush-tits at hand from the central 

 coast region of California, the Sacramento Valley, and the Sierra 

 Nevada, to indicate similar seasonal changes in these birds also, 

 though not enough material to illustrate every step of the trans- 

 formation at any one point. P. plumbeus, as shown by series of 

 skins from Arizona, Nevada, and east central California, undergoes 

 practically the same process of change, though being a more uni- 

 formly colored bird, the variations are not nearly so striking. 



As the described subspecies of the California Bush-tit, P. m. 

 calif ornicus, P. m. minimus, and P. m. saturatus, are largely dis- 

 tinguished bv varying intensity of coloration, it follows that there 

 is more or less ' overlapping ' of this character in the various forms. 

 Thus a faded example of minimus might be expected to bear a close 

 resemblance to a fresh fall specimen of califomicus, and similarly, 

 a late spring saturatus would be much like a newly molted autumnal 

 minimus. Of saturatus I cannot speak with certainty, having but 

 one or two specimens aN-ailable, but of minimus and californicm, 

 although the above statement is approximately correct, other 

 features remain which tend to distinguish the forms. 



There is, however, still another angle to the problem, for in birds 

 from different regions abrasion does not proceed with equal speed. 

 Tliis statement has also been made of the Red-winged Blackbirds 

 Mailliard, 1910, p. 64), and is probably true of most birds. In 

 general it appears that abrasion and fading produce much more 

 marked results in an arid than in a humid region, though, as stated 

 by Mailliard (I. c), other factors enter into the question also. 



