"Vol. XI~| r ID gway, Geographical Variation in Sialia mexicana. 1 47 



have a far greater amount of cinnamon or rusty coloring on the 

 under parts. 



(2) A series of nearly 50 adult males collected during the 

 breeding season on the higher parts of the San Pedro Martir 

 Mountains, Lower California, present as practically constant 

 characteristics several features which, individually, are very 

 rarely and in combination with one another never, seen in a still 

 larger series (82 adult males) collected in various portions of the 

 western United States and in Mexico. These peculiarities 

 of the Lower Californian bird consist in (1) the entire absence 

 or scarcely obvious development of chestnut on the back, (2) 

 separation of the chestnut on the breast into two lateral patches 

 by the longitudinal extension of the blue of the throat to that 

 of the belly, (3) greater average size, especially of the bill, and 

 (4) appreciably deeper, richer blue color of the upper parts, 

 with the blue of the throat — often that of the breast and upper 

 belly also — nearly or quite as intense ;is that of the upper 

 parts. 



(3) The extensive series from the western United States, repre- 

 senting numerous localities from southern California to Wash- 

 ington on the Pacific coast and western Texas to Colorado in the 

 interior, as well as from the northern and western States of 

 Mexico, show great variations in plumage which are of a 

 decided geographical significance 1 and may require subdivision of 

 the series into two forms. The birds of this series are almost 

 invariably smaller than those of the two preceding groups. They 

 have, with few exceptions, the back more or less extensively 

 chestnut, and the chestnut of the breast is almost invariably 

 broadly continuous anteriorly. 11131 specimens from Colorado, 

 New Mexico, Arizona, northern Mexico and western Texas all 

 but 2 (both autumnal birds from New Mexico) have the back 

 and scapulars 'solid' chestnut, at least laterally and, broadly, 



1 Professor Baird first called attention to these variations in 'Birds of North America' 

 (1858), p. 223, as follows : — 



"The reddish brown of the back and breast is in the form of lateral patches, meeting 

 more or less narrowly on the central line. Sometimes in the middle of the back it 

 does not meet at all, and at others it is quite broadly continuous. The latter is most 

 frequently seen in Rocky Mountain specimens. . . . Specimens from California 

 occasionally have but little brown on the back, but it is almost always distinctly 

 visible." 



