392 Cameron, Stoainsofi's Hawk in Montana. tauly 



found " a decrease of intensity of colour with a decrease of humidity, 

 the paleness evidently resulting from exposure and the blanching 

 effect of intense sunlight, and a dry, often intensely heated atmos- 

 phere." The same phenomena were observed in birds, on passing 

 from East to West, "the darker representatives of any species 

 occurring where the annual rainfall is greatest, and palest where 

 it is least." Thus, strong sunlight has a bleaching effect, while 

 a humid atmosphere causes intensity of pigmentation. 1 



With regard to the melanistic form of this hawk, Dr. A. K. 

 Fisher states (op. cit.): "From the above (grayish brown) there 

 are all phases of plumage to a uniform sooty brown"; and, in the 

 buzzard host observed by me in April, 1890, on the Powder River 

 (Auk, Vol. XXIV, p. 262) numbers of melanistic individuals were 

 present. In one day I beheld more of the latter than I have seen 

 in the last twenty-two years of the Western Red-tail (Buteo 

 borealis calurus) which is reputed to have a strong tendency to 

 melanism; but I have not met with flocks of the Red-tail like those 

 of Swainson's Hawk. 2 To sum up I consider that normal male 

 members of Swainson's Hawk have two dark and two light plum- 

 ages before becoming adult. According to my observations the 

 bird docs not breed until the fourth year, or until after it has 

 assumed the first light plumage. 



Female Plumage. 



As previously narrated, the female of my pair of Swainson's 

 Hawks escaped, and could not be captured, even with the aid of 

 a pony. I am thus unable to prove the following conclusions from a 

 captive specimen. In my opinion, the female has at least four 

 distinct plumages parallel with the male (two dark and two lighter) 

 and, like him, does not become fully adult until nearly five years 

 old. The two first plumages are indistinguishable from those of 



i Compare ' A History of Birds ' by W. P. Pycraft, p. S3, 1910. 



2 Melanotic examples of the Red-tailed Hawk may be seen here in the striking 

 plumage of chocolate-colored body and chestnut tail barred with black. In two 

 specimens before me the tail of one of these hawks has eight and of the other 

 twelve bars. 1 have never myself seen a black Swainson's Hawk with a notice- 

 ably light-colored tail. 





