Males fight for access to mates, both through scent marking and actual physical contact. Fights consist largely of biting and scratching and may result in serious injury. Gestation period in captivity is 27-32 days. Newborns weigh approximately 15 g. Eyes open at around 15 days old, and weaning occurs at 26-30 days. Males are heavier than females from early in development on.
Heavier females tend to have significantly more males in their litters than lighter females.
Females breed for the first time when they are yearlings. Behavior One of the most characteristic aspects of woodrat behavior is midden-building. Middens are often built in caves or crevices, and consist of plant material, feces, and other materials which are solidified with crystallized urine. Woodrat urine contains large amounts of dissolved calcium carbonate and calcium oxalates because of the high oxalate content of many of the succulent plants which make up the animals' diets. An important distinction to make is between middens and nests.