66 
THE CONDOR 
Vol. XVII 
themselves. They certainly cannot be as rigidly instinct-bound as are their 
less adaptable relatives. 
Confined to the drier western half of the continent are certain species 
which formerly lived in the mesophytie strips along the streams, but which 
since man's advent have more or less adapted themselves to the new conditions 
and have taken up sides with man. Two of especial note are the Brewer Black- 
bird and the Arkansas Kingbird. As for the first species, it is a peculiarly 
western bird, also of plastic habits and fearless mind, and so is widely spread. 
The Brewer Blackbird, formerly confined to the greasewood thickets and rose 
bushes along the desert streams, is now one of the ranch assistants, and builds 
its nest in any bush or vine that is convenient to its work about the garden 
or orchard. 
Fig. 19. An Arkansas Kingbird’s nest on top of a hay derrick, showing the possi- 
bility OF ENCOURAGING THESE BIRDS BY PLACING BOXES IN PROMINENT PLACES 
Perhaps one of the most striking adaptations shown by any of these bird 
pioneers is exhibited in the nesting sites chosen by the Arkansas Kingbird 
( Tyrann us verticalis). The Yakima Valley, eastern Washington, is especially 
suited to showing its preferences and range in choice of sites. The valley is 
long and narrow, and irrigation started many years ago in its upper end. 
Bv an intermittent development the area under cultivation was gradually 
extended downward until now it is irrigated for approximately forty miles 
of its length. In the upper parts, where irrigation has long since developed 
large trees, these birds seldom nest except in the larger forks of the taller 
