322 University of California Publications in Zoology [Vol. 16 



AERIAL HABITAT AND ASSOCIATION (BLUE MOUNTAIN AREA) 

 Minor : 



Empidonax difficilis difficilis — Empidonax hammondi — summer, 



summer. Empidonax wrighti — summer. 



Eeported : 



Chordeiles virginianus hesperis — Myotis longicrus. 



summer. 



Flycatchers, nighthawks, and bats make up the members of the 

 aerial association in the Blue Mountains. Swallows were seen flying 

 over some of the ridges but the species was not determined. 



CLIMATE 



Climatological records have been taken for a number of years in 

 southeastern Washington by Weather Bureau Stations. The accumu- 

 lated data have been kindly furnished by the United States Weather 

 Bureau. A summary of this is presented in Table 1. The data is most 

 complete for the prairie area and least so for the Blue Mountains. The 

 stations are usually located in towns and so the records do not indicate 

 the conditions in any particular habitat, but they do give a basis for 

 comparing the climatic conditions in different faunal areas. 



Table 2, which gives the climatological data for each month at 

 Walla Walla, is presented to illustrate the weather conditions in the 

 region at the different seasons. In southeastern Washington the pre- 

 cipitation is unequally distributed throughout the year, being greatest 

 in winter, while in summer very little rain falls. The summers are 

 very hot, and the winters moderately cool with occasional very cold 

 periods of short duration. There is a considerable daily range of 

 temperature and even in the hottest weather the nights are cool. The 

 humidity of the air is very low in summer, but is higher in winter. 

 There is an abundance of sunlight in summer, while in winter the 

 light is much weaker. Winds are quite common and especially in 

 spring may be very strong. Their usual direction is from the south- 

 west. A peculiar wind which deserves notice is the "chinook." This 

 is a drj', warm wind from the southwest which may start at any time 

 of the day or night in winter. It rapidly melts the snow and dries the 

 surface of the ground. In consequence, snow seldom lies for any 

 length of time upon the ground, except in the Blue Mountains. 



