Vertebrate Fauna of the Pacific Coast 

 felt beneath the surface of the ground and the vari- 

 ous lizards and snakes come out in force. 



The poisonous reptiles of the Southwest include 

 only the rattlesnakes, of several species, the Gila 

 monster, a huge lizard found only east of the Colo- 

 rado River, in southern Arizona and Mexico, and 

 the small red-banded snake, Elaps, also found in 

 southern Arizona and Mexico, but not west of the 

 Colorado River. The largest lizard next to the Gila 

 monster is the chuckwalla, a black-and-orange col- 

 ored reptile reaching a length of fifteen inches, and 

 stout-bodied in proportion, which lives on rocky 

 hills and may be seen in profile for considerable 

 distances as it rests at the summit of some boulder. 

 The fleet-footed leopard lizards and whip-tails are 

 among the first to attract the attention of a rider 

 across the desert. Finally there is the desert tor- 

 toise which lives in burrows which it excavates for 

 itself in sandy places and which wanders indiff"er- 

 ently over the vast stretches of the Mohave. (See 

 PI. XIII.) 



One wonders how such a prolific reptile popu- 

 lation secures a livelihood where vegetation is so 

 scarce; but it is only to be remembered that prac- 

 tically all parts of the southwestern deserts are sub- 

 ject to heavy rains at irregular intervals and that 

 these rains are followed by brief-lived but luxuriant 

 growths of herbs abundantly productive of seeds. 

 These seeds lasting over the periods of drouth form 

 the food of great numbers of insects, particularly 

 of ants and beetles, and also of rodents, and these 

 in turn are levied upon by the lizards and snakes. 



The reader is not meant to infer that the rep- 

 tilian life of the desert is its most numerous verte- 

 brate element. Experience on many parts of the 

 Mohave and Colorado deserts leads me to believe 

 that individually mammals outnumber reptiles and 

 birds combined. The seed-gathering types of ro- 

 dents, Dipodomys, Perodipus and Perognathus, pop- 

 ularly called pocket rats and pocket mice, are the 

 chief representatives. Other nocturnal rodents in- 

 clude white-footed mice, the carnivorous grass- 

 hopper mice, and desert wood-rats. Daylight- 

 roaming rodents are not wholly wanting and include 

 the striped antelope chipmunk which holds its short, 

 flat, white-lined tail closely appressed to its back, 

 the round-tailed ground squirrel, and the desert jack 

 rabbit. As with the reptiles, however, none of these 

 are abroad in the scorching midday sunshine, but 

 disport themselves actively only in the morning and 

 evening. There are also a few carnivorous mam- 

 mals, such as the big-eared kit fox, and a small, pale- 

 Ill 



