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 60 THE CONDOR Vol. XV pate, or to mark the instant' change in pitch from the shrill uproar of impending doom to the guttural notes of baffled retreat. The Falcon has a nasty temper at best, and if she dare not vent her spite on you, she will fall UlX)n the first wight who crosses her path. Woe betide the luckless Barn Owl who flaps forth from his polluted den hard by to learn the cause of the disturbance. I have seen such bowled into the sage in a trice, and Kelly declares that he has several times seen them struck dead. At such times also the Raven is put on trial for his life. In spite of their close association, there is evidently an ancient grudge between these birds. Whether or no the ebony saint be at fault, I cannot tell, but certain it is that if a Raven blunders near in the hour of the Falcon's high displeasure, he is fearfully beset. The Raven is an adept at wing-play himself, and the Falcon's thunderbolt is met with a deft evasion which reminds one of the best sword-play. But the Raven takes no pleasure in it. His eyes start with terror, and while he has no time for utterance himself, the distressed cries of his mate proclaim the danger he is in. This close association of Falcon and Raven at nesting time is the straugest element in the lives of both of them. To be sure their requirements of nest- ing sites are similar; but it is more than that which induces the hi'rds to nest within a hundred yards of each other in the same canyon, when neighboring or distant canyons offer- ing as excellent sites are empty. So constant indeed is this association that  when one finds the Raven's nest, he says, "Well, now, where is the Fal- con's?" Of the entire number of Raven's nests which came under my personal notice this year, seven were thus associated with the Falcon's in the same canyon, and the remain- ing three were within a quarter of a mile of Falcon's in neigh- Fig. 13. PIRA?I OV H CLOretS boring canyons separated by a single ridge. And it is impossible to tell from the stage of incubation reached which bird is the follower. In two in- stances, nests containing young Ravens were associated with Falcons whose eggs had not yet hatched; but in another notably close instance, the Raven laid her first egg on the day the Falcon's eggs were pipped. The remaining instances were teutral; i.e., nests of both species contained eggs. The only guess we dare hazard is that both birds reap advantages of warning in case of hostile ap- proach. Concurrent with this association is the annual, or at least occasionaI, shift- ing of sites on the part of both species. This shifting is of course quickened by persecution. If unsuccessful in raising a brood one year the bird will try. another situation, but always, except in extreme instances, in the same canyon or gen- eral locality. In this way the Falcon appropriates the site once occupied by Ra--