PRAIRIE FALCON 21 



The assaults of an angry Falcon are really dangerous. Even when the earliest 

 efforts are discouraged by a show of sticks or stones, it is decidedly disconcerting 

 to feel the rush of air from a passing falcon-wing, upon your hatless 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 upon the first wight who crosses 

 her path. Woe betide the luckless Barn Owl who flaps forth from his den to learn 

 the cause of the disturbance. I have seen such bowled into the sage in a trice. 



* * * 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. 



* * * The Raven is an adept at wing-play himself, and the Falcon's thunder- 

 bolt is met with a deft evasion. * * * But the Raven takes no pleasure in it. 

 His eyes start with terror, and while he has no time for utterance himself, the dis- 

 tressed cries of his mate proclaim the danger he is in. 



The close association of Falcon and Raven at nesting time is the strangest 

 element in the lives of both of them. To be sure, their requirements of nesting 

 sites are similar; but it is more than that which induces the birds to nest within 

 a hundred yards of each other in the same canyon, when neighboring or distant 

 canyons offering as excellent sites are empty. So constant indeed is this associa- 

 tion that when one finds the Raven's nest, he says, "Well, now, where is the 

 Falcon's?" Of the entire number of Ravens' nests which came under my observa- 

 tion in one year, seven were thus associated with nests of the Falcon in the same 

 canyon, and the remaining three were within a quarter of a mile of Falcons' in 

 neighboring canyons separated by a single ridge. And it is impossible to tell 

 from the stage of incubation which bird is the follower. * * * The only guess 

 we dare hazard is that both birds reap advantages of warning in case of hostile 

 approach. Concurrent with this association is the annual, or at least occasional, 

 shifting 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 general locality. In this way the 

 Falcon appropriates the site once occupied by Ravens (and so gets credited with 

 a "stick" nest, though I am satisfied that the Falcon never lifts a twig); and the 

 Ravens, in turn, without opposition, are allowed to rear their pile in a niche just 

 previously occupied by the Falcons. 



Decker and Bowles (1930) write that while potholes — 



are perhaps the favorite nesting sites of these birds, they are by no means the only 

 kind selected. In many cliffs there are no potholes at all, but on some projecting 

 ledge of rock a Western Red-tail or a Raven will have built its nest during some 

 past season, and it is the old nests of these two species that are very commonly 

 used by the Falcons. In fact, in many localities the abundance of the Falcons as 

 breeding birds depends entirely upon the presence of the old nests of these other 

 birds. An instance by way of proving this statement occurred to us in the past 

 spring when we visited a cliff where the year before we had found a Falcon using 

 an old Raven's nest. The nest had been dislodged by the winter storms and, as 

 there were neither old nests nor potholes, there were no signs of the Falcons to be 

 found anywhere in the vicinity. This is only one case in several that we have 

 noticed. In our experience the Falcons will always return to the old nest, even 

 though the rightful owners wish to take possession themselves. A very interesting 

 example of this was given us in the past spring of 1928, a somewhat detailed account 

 of which may be permissible. The nest in question was that of a Western Red- 

 tail, which was situated on a ledge about twenty-five feet from the ground and 

 some forty feet below the top of the cliff. We had taken a set of three eggs of the 



