180 University of California Publications in Zoology [Vol.12 



the Great Basin and northern Rocky Mountain region, where the 

 spring of the Transition zone dawns much later in the season, forcing 

 a much later nesting season. 



This idea is further borne out by a comparison of specimens. 

 Breeding birds from the Pacific Coast, selected as being fully adult, 

 are smaller throughout, with particularly less tumid bill than the Colo- 

 rado Valley birds of obvious maturity. The latter, however, in these 

 particulars, as well as in certain points of coloration, as extent of 

 black on head and extra amount of white on wings and tail, are 

 almost exact counterparts of breeding birds in the Museum collection 

 from the Pine Forest Mountains of northern Nevada. The May birds 

 of the Colorado Valley were thus evidently bound for the elevated 

 interior to the northward. The differences above referred to, as 

 exhibited between Pacific Coast black-headed grosbeaks and those of 

 the Rocky Mountain plateau, would appear to warrant recognition in 

 nomenclature, if for no other reason than to serve in designating their 

 separate course of migration. Ridgway (1901, p. 619) presents data 

 showing the differences in size and proportions, and also (I. c, p. 617) 

 refers to one of the color differences. But he does not consider the 

 races so distinguished worthy of naming. His synonymy (I. c, p. 

 620) would appear to show that the Rocky Mountain race should prob- 

 ably be called Zamelodia melanocephala melanocephala (Swainson) 

 while the Pacific Coast race should bear the name Zamelodia melan- 

 ocephala capitalis (Baird). 



Eleven examples of the black-headed grosbeak were secured on the 

 Colorado expedition, nos. 13433-13143. Among these is an aberrancy: 

 No. 13439 is a male of otherwise full plumage, except for the tail, in 

 which there is one old full-length, sticky and bedraggled feather, and 

 ten short feathers, newly unsheathing; this unusual condition at this 

 season was probably induced by loss of tail-feathers through some 

 accident. 



Guiraca caerulea lazula (Lesson) 

 Arizona Blue Grosbeak 

 First seen May 1, four miles below Potholes, two males; the next 

 day one male. Common at our station on the California side five miles 

 northeast of Yuma, May 3 and 4, as also on both sides of the river 

 in the vicinity of Pilot Knob. Observed here up to the time of our 

 departure. May 15. There was reason to believe that this Lower 



