39-2 CLARENCE HAMILTON KENNEDY. 



about the lower slopes of the Sierras. Thus nevadensis has a 

 habitat entirely above or outside of that of the other North 

 American members of the genus. 



We do not know the behavior complex of ^sJina nevadensis 

 in enough detail to speculate on all the adjustments in reactions 

 necessary to adapt this species of a lowland genus to a highland 

 habitat. It shares with all other /Eshnina?, and without any 

 change, a positive reaction to shining water surfaces when the 

 sexual instinct is not overbalanced by hunger. This is a reaction 

 through the eye as Anax, a related genus, was found reacting 

 just as positively to the glistening surfaces of the crude oil 

 pools of the Bakersfield (Calif.) oil field where hundreds of 

 Anax junius perished while mating and trying to oviposit in the 

 crude oil. When hunger predominates over the sexual impulse 

 the reactions change so that the ^Lshnas fly away from the water 

 on hunting trips into the surrounding territory. They fly aw r ay 

 from the water and roost on trees w r hen the minimum flying 

 temperature is reached, also at twilight on warm evenings when 

 the minimum flying light is reached. The minimum flying light 

 varies greatly with the different species as some will still fly 

 when it is so dark to the human eye that the dragonfly can be 

 seen only when it is outlined against the sky or some white 

 surface. 



As ponds for oviposition are the same on the Sierra upland 

 as at sea level, we find the reactions of nevadensis while under the 

 sexual impulse practically identical with the similar reactions of 

 the lowland species. The adjustments to the upland come in 

 the reactions of the insects when hunger and other impulses 

 outweigh the sexual impulses, and have nothing to do with the 

 coursing of the males and females over the surface of the water 

 while mating and ovipositing. 



Two of these adjustments to the conditions found in these high 

 altitudes are quite obvious. First the hunting individuals react 

 negatively to the warm stratum of air next the ground so that, 

 except early in the morning when the ground stratum of air is 

 still cool, they hunt high off of the ground flying from fifteen to 

 one hundred and fifty feet in the air. It is a tree-top species. 

 This positive reaction to cool air probably explains the attraction 

 of nevadensis to this alpine habitat. All other species of /Eshna, 



