°19i3 J Cameron, Notes on Swainson's Hawk. 169 



migration periods. Those interested can find a full account in 

 'The Auk' (Vol. XXIV, p. 262) of a buzzard invasion which I 

 witnessed on the Powder River, numbering nearly 2000 birds, 

 probably the largest aggregation of these hawks ever recorded. 

 Since the above event, which happened in April 1S90, other ob- 

 servers, as well as myself, have seen many smaller flocks of varying 

 numbers, while a small party of only seven birds was observed 

 by me on Sept. 27, 1911; but it may be hoped that the decrease 

 in size of the Montana migration does not afford a true indication 

 of the rate at which this species is diminishing. The earliest date 

 at which I have noted the spring arrival of a Swainson's Hawk was 

 March 14, 191 1 , and the latest fall lingerer was observed on Novem- 

 ber 25, 1910. 



The nests of B. swainsoni are made entirely of sticks, or of 

 sticks combined with' other materials, such as sage-brush, wild- 

 rose brambles, and cottonwood or cedar twigs. There may be an 

 elaborate lining of green weeds, or quantities of wool — perhaps 

 only a scanty layer of grass. Some birds line their nests with fresh 

 leaves, which are renewed at intervals, but, in my experience, 

 this docs not occur until after the full clutch of eggs has been laid. 

 The parent birds roll back the eggs and replace them on the leaves, 

 which is not a difficult feat, as many nests are almost flat. As the 

 hawk apparently mates for life, the nest, which is very strongly 

 put together, increases in size with the yearly repairs. In my own 

 experience I have known disused nests to be practically intact 

 after a period of seven or eight years. Since 1889, I have seen a 

 great many occupied nests, but only kept notes of fourteen. Of 

 these six were in ash trees, six in cottonwoods, one in a low cedar, 

 and one in a w ind-swept pine-top. This last, on a dominant scaur 

 of the pine hills, was the most picturesque of all, but could not, 

 of course, endure long without renewal, and is the only nest I have 

 Been thus exposed. 1 The number of eggs in seven nests was three, 

 in a couple of others two only : one nest was deserted after a single 

 white egg had been laid, and of four the contents were not examined 

 as I did not climb to them. Two fledglings seen in the tree do not 

 necessarily indicate two eggs, as in about half the clutches of three 



1 A photograph of this count ry was reproduced in 'The Auk,' Vol. XXV, 1908, 

 p. 251. 



