14 BIRDS OF THE PAPAGO SAGUARO NATIONAL MONUMENT. 



landscape that is more impressive than the giant cactus. The great 

 size of this plant gives it rank among its kind comparable to the 

 sequoia among forest trees, while in appearance it seems like a 

 weird intruder from another world or another epoch, among normal 

 and ordinary types of vegetation. To the botanist the giant cactus 

 presents its own problems, comprising peculiarities of distribution, 

 growth, and habits, difficult to understand and fascinating in their 

 complexity. To the student of birds it also makes _an appeal, for, 

 aside from the pleasure afforded from working amidst such pictur- 

 esque surroundings, the groves of giant cactus possess an assemblage 

 of bird species found practically nowhere else. 



On the desert, otherwise a land of low shrubs and bushes, this 

 towering cactus takes the place of trees, at least as regards the needs 

 of birds that dwell in hollows of tree trunks. Consequently, in those 

 sections of the country where it grows, we find a peculiar group of 

 birds, desert species purely, but prototypes of woods-dwelling forms 

 of other sections. With them there are associated certain species 

 which elsewhere occupy woodland, and which here find suitable nest- 

 ing sites within the cactus or in the crotches of its branching arms. 



Following are the birds forming the " giant cactus association " 

 in Arizona that is, those species whose occurence in a region is de- 

 pendent'^iilirely^ej: in large part, upon the presence of the cactus: 

 Saguaro screech owl^elf owl, Gila woodpecker, Mearns gilded flicker, 

 anaA-riaeftarcTested flycatcher. With these are often associated 

 other birds who gladly take advantage of nesting sites in or upon the 

 cactus, but which also occur in woode^secjions^in other parts of the 

 country. These ttreTWestern (red^tailed h^wi, Swainson hawk, 

 America^ sparrow hawk\ wesrem^horned owl, ash-throated fly- 

 catcher, purple- martin,- -and touse fincfn tT/nave even found the 

 mourning dove sitting upon eggs4n_a_g.gug^d-out cavity in the side 

 of a Sgliartxtrunk. 



The elf owl,Vilded flicker, and Arizona crested flycatcher may oc- 

 casionally bejfound nesting in holes in trees where such occur near 

 the gianTcactus, but it is useless to look for them in sections of the 

 country where the cactus does not also grow. So closely are these 

 species confined to the neighborhood of the giant cactus that they 

 appear to have been evolved in direct response to the opportunities 

 afforded by this plant to these types of birds. In other words, to 

 put it baldly, here were niches, to be filled in by a hole-dwelling owl, 

 woodpecker, and flycatcher opportunities not found elsewhere 

 in these desert countries, and promptly taken advantage of by types 

 of birds which in other sections would find suitable homes in the 

 timber. The sparrow hawk and purple martin utilize holes in the 

 cactus as they would in trees or buildings. The cactus wren some- 



