RODENTIA 271 



largely useful grasses, one den having contained 680,000 separate 

 pieces. The ground within a radius of from 15 to 25 feet about the den 

 may be denuded of vegetation. 6 



On a range of 50 square miles in Arizona it was estimated that, al- 

 lowing 50 pounds of forage daily as the need of each steer, the forage 

 consumed by the large kangaroo rats (Dipodomys spectabilis) would 

 be enough to feed 14 steers. 7 In another paper the same authors say 

 25 pounds of forage per steer would be enough, which would double 

 the number of steers the forage consumed by the kangaroo rats would 

 support. They also report that 592 barn owl pellets contained remains 

 of 230 kangaroo rats. 8 



Bailey's Texas report furnishes the following items: 9 Richardson 

 kangaroo rat (Dipodomys ordii richardsoni) : "the food of this, as of 

 other species of this genus, is almost entirely seeds, including those of 

 many grasses, various native plants, and any of the small grains"; 

 and, though usually harmless, when abundant they sometimes become 

 destructive. Ord kangaroo rat (D. ordii) was found to be feeding "on 

 seeds of wild sunflower, Parosela and other wild beans." Padre Island 

 kangaroo rat (D. compactus) feeds on seeds of a small plant like 

 purselane and takes oatmeal readily as bait in traps. Loring kangaroo 

 rat (D. elator) : one caught in a Kafir corn field contained 100 seeds 

 of Kafir corn and 65 seeds of Solatium rostratum. One carried off and 

 stored two bushels of wheat. One was taken from a large rattle- 

 snake. Texas spiny pocket mouse (Liomys irroratus texensis} feeds 

 "on the seeds of hackberry, mesquite and various other shrubs." 



Dwarf pocket rat or kangaroo mouse (Microdipodops megacepha- 

 lus) : food "consists mostly of seeds,'- the cheek pouches containing 

 seeds of Gilia and Oryzopsis, and one containing an insect larva. 10 



FAMILY CASTORIDAE BEAVERS 



It has been said that "the beaver is the most important fact in 

 American history," 1 because it was long the backbone of the fur 

 trade, the chief industrial and commercial enterprise in the vast in- 

 terior of the continent for three centuries. The quest for beaver and 



' Taylor, Scientific Monthly, xxi, 2, 1925. 



* Vorhies and Taylor, Life history of the kangaroo rat, U. S. Dept. Agric. Bull. 

 No. 1091, p. 37, 1922. 



8 Vorhies and Taylor, Damage by kangaroo rats, Journ. Mammalogy, v, 144, 1924. 



"Bailey, Biological survey of Texas, N. Amer. Fauna, No. 25, pp. 127, 144-149, 

 1905; see also No. 49, p. 124, 1926; Farmers' Bull, No. 335, p. 22, 1908. 



10 Hall and Linsdale, Notes on the life history of the kangaroo mouse (Micro- 

 dipodops), Journ. Mammalogy, x, 295-305, 1929. 



1 Science, XLI, 2/6, 1915, quoting Merriam. 



