222 BULLETIN 16 7, UNITED STATES NATIONAL MUSEUM 



BUTEO SWAINSONI Bonaparte 

 SWAINSON'S HAWK 



HABITS 



This highly beneficial and almost entirely harmless hawk enjoys a 

 wide distribution over the western half of North America and a 

 large part of South America, where it is one of our commonest 

 Buteos. It is essentially a bird of the wide open spaces, prairies, 

 plains, and even deserts. Major Bendire (1892) says: "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, per- 

 haps, all the other Kaptores of these regions combined. It is emi- 

 nently a prairie bird, shunning the densely timbered mountain 

 regions, and being more at home in the sparingly wooded localities 

 found along the water courses of the lowlands." 



Spring. — Swainson's hawk is a highly migratory species, winter- 

 ing mainly south of the United States and returning to its northern 

 breeding grounds in spring in spectacular flocks or waves. Refer- 

 ring to Escondido, Calif., C. S. Sharp (1902) writes: "The Swain- 

 son hawks arrive here from the south about the 10th to 20th of 

 March, sometimes in large flocks or in bands of a dozen or two. The 

 earliest and largest flocks all go north, the summer residents not 

 coming until a couple or three weeks later, and going at once to their 

 quarters which they refit preparatory to permanent occupancy 

 later on." 



In El Paso County, Colo., Charles E. H. Aiken (1914) noted these 

 hawks migrating in numbers as early as March 11, during a light 

 snow fall, and as late as April 20, "a bright sunny day succeeding a 

 period of stormy weather." These were all melanistic birds, though 

 "nearly all Colorado breeding birds are of normal coloration," M, P. 

 Skinner says in his notes that in Yellowstone National Park it comes 

 later and departs earlier than the redtail. Its arrival in spring 

 varied from April 18, 1920, to May 3, 1921, sometime after the ap- 

 pearance of the ground squirrel. 



E. S. Cameron (1907) gives the following account of a remark- 

 able flight observed in Montana: 



My first introduction to tliese hawks was in April, 1890, when an extraordi- 

 nary invasion of them — probably nearly two thousand birds — alighted around 

 the ranch where I was staying on the west bank of the Powder River. They 

 came in the afternoon from a southerly direction and, for a time at least, fol- 

 lowed the downward course of the river, as a neighbor living above reported 

 the enormous hawk army which flew over. The wide river bottom where the 

 ranch is situated is thickly overgrown with cottonwoods, and the fence of the 

 saddle horse pasture all l)ut joins the buildings. When the last birds had ar- 

 rived, the trees inside this pasture were simply black with them ; but as there 



