179 

 Notes on certain Californian Diurnals. 



It lias probably been remarked by all wlio have collected on 

 the Pacific coast that the fauna changes most strikingly with a 

 change of level. At times, in the mountainous districts, a walk of 

 five or six kilometi'es will suffice to transport the collector into 

 a faunal region more distinct from the one just left than any that 

 mio-ht be found in a journey of many hundred kilometres alojig 

 the coast. This circumstance is so noticeable that it leaves the 

 impression that more than ordinary differences of climate must 

 be at work to accomplish such marked results ; a little calcula- 

 tion, however, will show that the climatic alteration due to 

 elevation alone is sufficient to account for all the changes that 

 we see. 



A journey due north of five thousand kilometres from cen- 

 tral California would bring the explorer to hyperborean regions, 

 while a rise of 4500 metres would cause an equivalent change 

 in external conditions of life ; and I think that it will not be far 

 wrono; to assume that the changes for each 300 metres elevation 

 are equivalent to, though of coui'se not identical with, the 

 changes which would be noted in a journey of 325 kilometres 

 along the coast or at a uniform level. 



Though there is not such a sharply defined limit to the truly 

 alpine fauna as we find in the Rocky Mountains, where this is 

 coincident with the timber line, usually at about 3350 metres 

 above the sea, yet in the Sierra Nevada we can trace a pretty 

 distinct line below which the sub-alpine species rarely stray in any 

 numbers, and this limit at the Yo Semite valley is at from 1800 

 to 2100 metres above the sea. It is somewhat remarkable that 

 in this valley the line should be traceable at all, for the cliffs are 

 so high that it would take but little fluttering for a butterfly to 

 descend a thousand metres, in many places, to the floor of the val- 

 ley. It is impossible to doubt that this often occurs; thus Par- 

 nassius haldur Edw., which usually inhabits a sub-alpine district, 

 was occasionally found flying over the meadows, at the base of 

 the cliffs, and Papilio indra^ which seems most at home at an 

 elevation of 2750 to 3000 metres, was several times observed 

 and captured one and a half kilometres beneath its usual level. 



