November 3, 1905.] 



SCIENCE. 



551 



East of the Rocky Mountains, in the 

 same region as the typical leucophrys, we 

 have the white-throated sparrow, with yel- 

 low in front of the eye, and some other dif- 

 ferences. This is Zonotrichia alhicollis. 

 It does not cross the mountains and no sub- 

 species are recognized, unless indeed the 

 species Zonotrichia leucophrys be one of 

 the oft'shoots. Two other species, distinct 

 so far as we know, are recognized, Zono- 

 trichia coronata, the golden crowned spar- 

 row, breeding in Alaska, and the stately 

 Harris sparrow, Zonotrichia querula, of 

 the interior plains, migrating from Mis- 

 souri and Minnesota to the Saskatchewan 

 ^region. In this species the top of the head 

 is black, wdth stripes of either white or 

 yellow. 



Besides these differences of color, each 

 species has some slight peculiarity of form. 

 Zonotrichia alhicollis, for example, having 

 a rounded wing and Zonotrichia coronata 

 a longer tarsus than the other species. 



In a discussion of the origin of certain 

 species of chickadee Joseph GrinnelP makes 

 the following observations: 



It is isolation, either by barriers or by suffi- 

 cient distance to more than counterbalance in- 

 heritance from the opposite type that seems to 

 me to be the absolutely essential condition for 

 the differentiation of two species, at least in birds. 

 A strong argument in support of this conviction 

 is that we never find two ' subspecies ' breeding in 

 the same faunal area, and no two closely similar 

 species, except as can be plainly accounted for by 

 the invasion of one of them from a separate center 

 of differentiation in an adjacent favmal area (ex- 

 ample, Parus rufescens of the West Coast fauna, 

 and Parus gamheli of the arid Sierras meet in 

 the Siskiyou mountains). * * * 



The extremest intra-competition does not en- 

 sue until after further discrimination is impos- 

 sible. * * * 



Two species of approximately the same food hab- 

 its are not likely to remain long evenly balanced 

 in the same region. One will crowd out the other: 

 the one longest exposed to local conditions and 

 hence best fitted though ever so slightly will sur- 



1 Auk, July, 1904, p. 372. 



vive to the exclusion of any less favored invader. 

 However, should some new contingency arise, plac- 

 ing the native species at a disadvantage, such as 

 the introduction of new plants, then there might 

 be a fair chance for a neighboring species to gain 

 a foothold, even ultimately crowding out the na- 

 tive form. For example, several pairs of the 

 Santa Cruz chickadee {Pants rufescens harloioi) 

 have taken up their abode in the coniferous por- 

 tion of the arboretum at Stanford University, 

 while the plain titmouse prevails in the live oaks 

 of the surrounding valley. 



* * * The greatest rate of reproduction is 

 presumably where the species finds itself best 

 adapted to its environment, and this is also where 

 the death rate is least, unless an enemy rapidly 

 multiplies so as to become a serious check. * * * 

 In wide ranging species subcenters arise. * * * 

 From each of these new centers of distribution, 

 there will be a yearly radiating flow of individ- 

 uals into the adjacent country so as to escape 

 intra-competition at any one point. 



Not long since the writer addressed to 

 certain leading ornithologists of the United 

 States a circular letter, as given below. 

 Certain typical answers to this letter are 

 appended, all agreeing in general with the 

 proposition stated above. 



In considering the proposition that species in 

 general arise in connection with geographic or 

 topographic isolation, will you kindly answer 

 briefly the following questions ? 



1. Do two or more well founded subspecies ever 

 inhabit [breed in] the same region? If so, give 

 examples. 



2. If so, how do you explain the fact? 



3. Would you regard a form as a ' subspecies ' if 

 coextensive in range with the species with which 

 it intergrades ? 



4. Are there cases where two species inhabiting 

 exactly the same region are closely related, and 

 more closely than any other species is in either 

 one ? If so, give examples. 



LEONARD STEJNEGER. 



Before answering the four questions contained 

 in your letter of February 21, just received, allow 

 me to make a few general remarks. 



I suppose that by inhabit you mean propagate, 

 since many migrating subspecies spend part of 

 their time in the territory of the other subspecies. 

 It may probably be necessary to fui'ther qualify 

 the word propagate by adding simultaneoitsly, 



