NATURAL SCIENCES OP PHILADELPHIA. 41 



is that it is nearly upon the dividing line between two tracts of country quite 

 diverse from each other in those points which chiefly affect the distribution 

 and migration of species. A single day's journey to the southward gives us 

 changes in the birds, so great, that I do not hesitate in comparing the differ- 

 ence to that which exists between the Middle Atlantic and the Gulf States, in 

 the eastern Province. Very numerous species,* not detected at any season at 

 Fort Whipple, are yet found abundantly within fifty miles to the south and 

 southwest. At the same time the locality is a true component of the eleva- 

 ted and cold regions to the northward, and assimilates in this respect to Utah 

 and Nevada. Intermediate in situation between the two great valleys of 

 southwestern United States those of the Rio Grande and Colorado Rivers, it 

 draws tribute in a measure upon each of them, though, as might be supposed, 

 vastly more from the latter than the former. In this connection I may advert 

 to an interesting point, which I consider as quite probable, though contrary 

 to the usual laws of migration ; viz., that many of the birds of the Colorado 

 vallej, which are there winter residents, instead of migrating far to the north 

 in spring, by turning simply to the eastward, find in the region of which 

 Fort Whipple is the southern limit the conditions necessary for breeding 

 grounds. That such is a fact would seem to be indicated by comparing the 

 forms common to both Mojave and Whipple; the summer residents or spring 

 migrants of the latter place being usually winter residen's at the former 

 locality ; but can only be incontrovertible* proven by showing that some 

 species wintering at Mojave are not found directly north of that point in 

 summer ; and that they do breed in the Whipple mountains. 



The seasons are well pronounced at Fort Whipple, and do not differ nota- 

 bly from those of the Middle Atlantic States. This enables us trenchantly to 

 divide those of its birds which are not permanent residents, into summer and 

 winter residents, and migratory species passing through in the spring and 

 autumn. And I have noticed in many instances that the times of arrival and 

 departure of non-residents are strikingly similar to those of the migratory 

 species passing through Washington, D. C. Quite the reverse is the case in 

 southern Arizona ; where the protracted heat and drought of a long summer, 

 which encroaches on intermediate seasons, disturbs the regularity of migra- 

 tion ; or even entirely takes away from some species the migratory impulse. 



The immediate vicinity of Fort Whipple is admirably adapted to ornitho- 

 logical pursuits in the very varied character of surface presented within the 

 compass of a day's walk. Pines constitute the main feature of the Sylva, 

 covering all the mountains down to what may be considered as the average 

 altitude of the locality. .An extensive undulating plain stretches to the north- 

 ward, partially grassy, partially covered with the characteristic shrubs of 

 the country. Ranges of broken low hills, sparsely covered chiefly with sev- 

 eral species of dwarf oak, or so nearly naked as to be little more than huge 

 masses of metamorphic rocks, attract their share of species. The head of 

 one of the forks of the San Francisco River flows past; at times a considera- 

 ble stream, but usually dry. The vegetation along this, as well as all other 

 water courses of the Territory, has as its most prominent element the ever 

 present Populus moniliferus ; together with species of Salix, Primus, Castanea, 

 etc., the bases of which trees are as usual tightly sewn together by a tangled 

 matted network of rank undergrowth ; the whole forming a tract peculiarly 

 yielding, as every ornithologist knows, of variety and value in specimens. A 

 small rather open swamp near by affords several species, which, but for its 

 presence, would not form a part of the birds of the locality. 



By adding to the species observed at Fort Whipple, and characteristic of 

 that locality, such others as have been ascertained to inhabit any portion of 

 the Territory, the subjoined list becomes an exposition of the present state of 



* For example: Chordeiles texensis, Pyrocepho.lus mexicanus, Catherpes mexicanus, Vireo pusillus 

 (a. sp.,) Pipilo Abertii, P. mesoleueus, etc., etc. 



1866.] 



