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THE AMEBIC AN NATURALIST [Vol. LI 



thus proven not to be affected by atmospheric pressure, or by 

 atmospheric density, at least in as far as it is modified by alti- 

 tudes up to 12,000 feet. The same fact — depression of range 

 towards the north — discloses a third concomitant of altitude, 

 which is also a concomitant of latitude, namely, temperature, 

 and this is beyond doubt the determining factor. As the iso- 

 therms dip toward sea level to the northward so does the range 

 of the genus Ochotona. We have, therefore, by study of geo- 

 graphical distribution in this case established two important con- 

 trolling factors, namely (1) safety refuges of a sort provided by 

 talus slopes and glacial moraines; (2) temperature, at least 

 downward below the degree, correlated in the mountains of Cali- 

 fornia by a mean annual or summer computation or for a briefer 

 period at the time of reproduction, with an altitude of eight to 

 twelve thousand feet, according to latitude, slope exposure and 

 air currents. 



It is not possible for one to say from the data in hand what 

 the direct controlling factors of the upward limits of the cony's 

 range may be. Taluses extend up to the highest peaks, but there 

 is no growth of grass above about the 12,000-foot contour even on 

 the most favorable slopes. As the disappearance of the cony in 

 the higher altitudes is coincident with the disappearance of its 

 food, it appears as if failure of food alone were the delimitor 

 here ; but we have no way of showing that even if food did con- 

 tinue the cony would be restricted upward, as it certainly is 

 downward, by a change in temperature beyond some critical 

 point. The cause of its delimitation downward, however, re- 

 mains clear. 



The Case op the Rosy Finch 



In the case of the bird called generically Leucosticte, or rosy 

 finch, we find a condition astonishingly similar to that of the 

 cony. In fact almost the entire preceding account could be 

 made relevant here, by merely substituting the term rosy finch 

 for cony. The ranges, altitudinal and geographical, of the two 

 animals are almost identical. The only obvious differences ap- 

 pear in their ecologic relations, and consist in the lesser de- 

 pendence of the bird upon shelter and in the dissimilar nature 

 of its food. The rosy finch forages gregariously on the open 

 slopes, near timberline and above, though its nest is hidden 

 Away in the clefts of rock ledges and taluses. It shuns the trees 



