1916] Dice : Land Vertebrates of Southeastern Washington 331 



Life-Zones op Southeastern Washington 



The sagebrush region about Wallula belongs certainly to the Uiiper 

 Austral life-zone. It is placed in this zone on the basis of the flora 

 by Piper (1906, p. 35). Merriara (1898, p. 30) states that a part of 

 the Upper Austral zone in Washington, in the valleys of the Snake 

 and Columbia rivers, has so hot a climate that it might almost be 

 placed in the Lower Austral zone. 



The Columbia Basin prairie area must be placed in the Transition 

 life-zone although it contains a strong Upper Sonoran element. In 

 the area there are no species which have not elsewhere been reported 

 to occur in zones above the Upper Sonoran. Four breeding species, 

 Mustela arizonensis, Citellus columbianus colnmbianus, Passerella 

 iliaca schistacca, and Opeirornis tolmiei, are characteristic of the 

 Transition or higher life-zones. Further, the area has been placed in 

 the Transition life-zone by Piper (1906, p. 48) on the basis of the 

 flora. 



In the Transition life-zone must be included the bunchgrass hills 

 south of Wallula and also those north of the Walla Walla River east 

 of Nine-mile. Sagebrush as a dominant habitat extends up the Walla 

 Walla Valley as far as Touchet, and this woidd seem to mark the 

 eastern limit of the Upper Austi'al life-zone in the region. Piper 

 (1906, map) extends a tongue of Upper Austral as far east as Walla 

 Walla, but there seems no justification for this, for the plant and ani- 

 mal associations at Walla Walla, so far as can be judged under the 

 present altered conditions, are essentially the same as in the bunch- 

 grass region to the north and east. Piper also places the caiiou of 

 Snake River, for the whole of the distance that this extends through 

 Washington, in the Upper Austral life-zone. However, in the canon 

 of Snake River at Lyon 's Ferry sagebrush was not the dominant vege- 

 tation and the characteristic vertebrates of the Upper Austral life- 

 zone found at Wallula were not present. 



Temperature records of the kind used by Merriam (1894) in de- 

 fining the limits of the life-zones are available only for Walla Walla 

 (Bigelow, 1908, p. 90). At Walla Walla daily normal temperatures 

 of 43° F. and above occur throughout the period between March 12 

 and November 16, giving an average growing season of 249 days. The 

 sum of the daily normal tempei'atures for this season is 15352° F. 

 The hottest six weeks of summer at Walla Walla are the last three 

 weeks of July and the first three weeks of August. The average tem- 



