236 LIFE HISTORIES OP NORTH AMERICAN BIRDS. 



About one-third of the eggs are unspotted. In shape they vary from an 

 elliptical oval to an oval. Now and then one occurs that may be designated 

 as elliptical ovate. The shell is fairly smooth and close grained. 



The average measurement of fifteen eggs of this species in the U. S. 

 National Museum collection is 60 by 47.5 millimetres; the largest egg meas- 

 uring 65 by 50, the smallest 55 by 44 millimetres. 



The type specimen No. 22581, selected from a set of three, taken March 8, 

 1882 (PL 7, Fig. 8), is the heaviest marked egg of the series, but in another 

 egg of this set the spots, while fewer, are darker colored, and No. 22583, from 

 a set of two, taken April 4, 1885 (PL 7, Fig. 9), shows but a trace of a faint 

 spot here and there, and resembles an unspotted egg. Both these sets were 

 obtained in exchange from Capt. B. F. Goss, and were taken near Corpus 

 Christi, Texas. 



81. Buteo swainsoni BONAPARTE. 



SWAINSON'S HAWK. 



Buteo swainsoni BONAPARTE, Geographical and Comparative List, 1838, 3. 

 (B 18, 19, 21, 28, C 354, R 442, C 523, U 342.) 



GEOGRAPHICAL RANGE: Western North America; north to Alaska and western side 

 of Hudson Bay; east to Wisconsin, Illinois, and Arkansas (casually to Massachusetts); 

 and south through Central America and greater part of South America to the Argen- 

 tine Republic. 



Swainson's Hawk has a wide distribution during the breeding season. 

 Commencing with the southern portion of its range east of the Rocky Moun- 

 tains this includes portions of the less densely timbered and prairie regions 

 of Texas and Arkansas thence northeastward in similar localities to Illinois 

 and Wisconsin; north and westward through the intervening States and Tern 

 tories into the Dominion of Canada from Manitoba, westward and north to 

 the Arctic regions in about latitude 65. West of the Rocky Mountains it 

 is found in New Mexico and Arizona, and over the entire Pacific coast region 

 north into British Columbia and Alaska. 



On the arid wastes and table lands of southern Arizona, as well as in the 

 sage and bunch grass districts of Nevada, Oregon, Washington, and Idaho, 

 Swainson's Hawk is especially abundant, outnumbering, perhaps, all the other 

 Raptores of these regions combined. It is eminently a prairie bird, shunning 

 the densely timbered mountain regions, and being more at home in the 

 sparingly wooded localities usually found along the water courses of the low- 

 lands. 



Compared with the majority of our Hawks it is gentle and unsuspicious in 

 disposition, living in perfect harmony with its smaller neighbors. It is no 

 unusual sight to find other birds, such as the Arkansas Kingbird, Tyrannus ver- 

 ticalis, and Bullock's Oriole, Icterus bullocki, nesting in the same tree; and the 

 first-mentioned species goes even further than this, sometimes constructing its 



