472 FIELD STUDY IN ORNITHOLOGY. 



iusular expeiieiice, I .should be iuclined to believe that the theory of 

 interbreeding is beginning at tlie wrong end, but rather that, while 

 the generalized forms remain in the center of distribution, we find 

 more decidedly distinct species at the extremes of the range, caused 

 not by interbreeding, but by differentiation. To illustrate this by the 

 group of the blue titmouse. We find iu Central Russia, in the center 

 of distribution of tlie family, the most generalized form, Fariis 2>Jcslii, 

 partaking of the characters of the various species east, west, and south. 

 In the northeast and north it becomes differentiated as P. cyaneus; to 

 the southwest and south into P. cfvndcKs ami its various subsi)ecies, 

 while a branch extending due east has assumed the form of Pjiavipec- 

 ens, bearing traces of affinity to its neigld»or P. vyanens in the north, 

 which seems evidently to have been derived from it. 



But the scoi>e of tield observation does not cease with geographical 

 distribution and modification of form. The closest systematist is very 

 apt to overlook or to take no count of habits, voice, modification, and 

 other features of life which have an important bearing on the modifica- 

 tion of species. To take one instance, the short-toed lark {Calandrella 

 hraehydartyla) is spread over the countries bordering on the Mediterra- 

 nean; but along with it, in x\ndalusia alone is found another species, 

 Cal. b(vti(la, of a rather darker color, and with the secondaries generally 

 somewhat shorter. Without further knowledge than that obtained from 

 a comparison of skins, it might be put down as an accidental variety. 

 But the field naturalist soon recognizes it as a most distinct species. 

 It has a different voice, a differently shaped nest; and, wlnle the com- 

 mon species breeds iu the i^lains, this one always resorts to the hills. 

 Tlie Spanish shei^herds on the spot recognize their distinctness, and 

 have a name for each species. Take, again, the eastern form of the 

 common song thrush. The bird of North China, Turdus auritus, closely 

 resembles our familiar species, but is slightly larger, and there is a 

 minute difference in the wing formula. But the field naturalist has 

 ascertained that it lays eggs like those of the missel-thrush, and it is 

 the only species closely allied to our bird which does not lay eggs of a 

 blue ground color. The hedge accentor of Japan {AocoUor ruhidufi) is 

 distinguished from our most familiar friend, Accentor modnlari'^, by 

 delicate differences of hue. But, though in gait and manner it closely 

 resembles it, I was suri)rised to fine the Japanese bird strikingly dis- 

 tinct in habits and life, being found only in forest and brushwood sev- 

 eral thousand feet above the sea. I met with it first at Chinsenze— 

 (),000 feet, before the snow had left the ground, and in summer it goes 

 higher still, but never descends to the cultivated land. If biTth species 

 are derived, as seems probable, from Accentor immaculatus of the Hima- 

 layas, then the contrast in habits is easily exj^laiued. The lofty moun- 

 tain ranges of Japan have enabled the settlers there to retain their 

 original habits, for which our humbler elevations have afforded no 

 scope. 



