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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 me?ophytic 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 KINGBIBDJS NE?ST ON TOP OF A I-IAY DERRICKj SI-IOWlNG TI-IE POSSI- BILITY OF ENCOURAGING TI-IESE BIRDS BY PLA?ING BOXES IN PP, I)/?INE?T 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 (T?rannus 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 ypars ago in its upper end. By an intermittent development the area urider cultivation was gradually extended'downward until now it is i?rigated for approx.imately forty miles of its length. In the upper parts. where irrigation has long since developed large trees. ?hese birds seldom nest except in the larger forks of the taller