228 



MAMMALS OF AMERICA 



On desert plains a thick clump of cactus or other 

 thorn V vegetation is frequently chosen as the nest 

 site, and here pieces of cactus are the chief ma- 

 terial used in construction. Often the entire nes: 

 is a bristling mass of thorns, and as a further 

 protection some especially spiny sections are 

 placed about the openings and along the smoothly 

 worn runways. \Mien it is remembered that 

 manv of the spine.'^ have barbed points sharper 

 than needles, which enter the flesh at the slightest 

 touch, it is difficult to understand how the 

 builders transport such material or are them- 

 selves able to travel without being pierced. 



Wood Rats are expert climbers, and some 

 species, in addition to building surface nests three 

 to five feet in height, often place them twenty 

 feet or more from the ground among the upper 

 branches of trees. None of the species is 

 known to enter water voluntarily, but in Mexico, 

 near the borders of lagoons, at least one of the 

 species occ.:.sionally builds nests in the tops of 

 mangroves, from which a single well-worn route 

 always leads through the thick branches out to 

 feeding grounds on the shore, perhaps fifty or 

 seventy-five yards away. \\'ood Rats do not 

 frequent towns, but often live in the vicinity of 

 farmhouses, and have been known to carry of? 



spoons, knives, forks, pieces of cloth, and many 

 other articles, and add them to their nests. 



They are chiefly nocturnal in h'abits. but some 

 are partly diurnal. Their food is largely deter- 

 mined by varying local conditions, but consists 

 mainly of a great variety of green vegetation, 

 including grass, leaves, fresh fruit, small bulbs, 

 bark, and cactus stems. Dry seeds, nuts and 

 fungi are also eaten. During successive seasons 

 of drought in the Rio Grande valley, when ordi- 

 nary food is scarce and in consequence most 

 small mammals are greatly reduced in numbers, 

 \\'ood Rats maintain their usual abundance by 

 recourse to the large, soft, juicy cactuses. 



\\'ood Rats have numerous deadly enemies 

 such as owls, hawks, snakes, wild cats, civet cats, 

 coyotes, foxes and probably weasels, which serve 

 to keep their numbers in check. Some of the 

 desert ?.pecies are sufficiently numerous to inflict 

 appreciable damage on growing crops in fields 

 and gardens and to carry off considerable grain 

 stored on farms, but they have not thus far 

 proved as injurious as some other rodents. In 

 the arid regions of the Southwest they girdle and 

 kill many native shrubs and severely injure 

 cactuses, especially during the long dry season 

 when food is scarce. 



COTTON RAT 



Sigmodon hispidus Say and Ord 



Other Name. — Marsh Rat. 



General Description. — A fairly large rodent inter- 

 mediate in size between the House Mouse and the 

 common Norway Rat. Head rather broad : nose 

 pointed : ears nearly hidden in the long hair ; body 

 fairly thickset: tail slender, scaly, thinly haired, shorter 

 than head and body ; legs short, slender ; pelage long, 

 coarse, hispid ; color above, grayish-buff grizzled with 

 black ; below, dull white. 



Dental Formula. — Incisors, ■!=-': Canines. ^=? : Pre- 



I — I' — o ' 



molars. 



Molars, 



^=16. 



o — o ' 



Pelage. — ."Xdults : Sexes identical, seasonal varia- 

 tion very slight. Above, pale yellowish-gray, coarsely 

 grizzled with black, paler on sides ; lower parts ashy 

 or dull white ; ears plumbeous at base : feet grayish- 

 white ; tail blackish above, grayish below. YoUNC : 

 Similar to adults but grizzled appearance lacking. 



Measurements. — Total length, lo inches; tail verte- 

 brae, 4 inches; hind foot, 1.3 inches. 



Range. — Eastern United States. Carolinas to Florida. 



Food. — Seeds, grasses and green vegetation ; occa- 

 sionally flesh. 



Remarks.— The Cotton Rats are related to the Rice 



Rats but because of their coarse hair and bristling coat 

 they are not liable to be confused with any other 

 rodents. Like the Rice Rats, this group is of southern 

 origin and only the northern forms come into the 

 United States. Eight species and subspecies of this 

 rodent are found north of the Rio Grande, but this 

 genus is distributed well down into South .America. 



Rel.\ted Species 



Cotton Rat. — Sigmodon hispidus hispidus Say and 

 Ord. Typical animal as described above. Carolinas 

 to Florida 



Texas Cotton Rat. — Sigmodon hispidus tcxiaiius 

 (.\udubon and Uachman). Smaller than the Common 

 Cotton Rat. Texas and Oklahoma. 



Pallid Cotton Rat. — Siijiiiodou Iiispidiis bcrlandicri 

 (Baird). Small; ears larger; color paler than common 

 Cotton Rat. Eastern desert tract upper Rio Grande. 

 Texas and New Mexico. 



Least Cotton Rat. — Sigmodon minimus Mearns. 

 L'nderfur dark; ears, feet and tail densely haired; 

 grayish mixed with blackish and light yellowish-brown. 

 Mountains of southern New Mexico, Arizona and south 

 into ^lexico. 



