Northern lowland and southern lowland populations may not be in contact, however. We have two specimens from the supposed hiatus, from one mile north and two miles east of San Antonio, Socorro County, but the first specimen is a skull only, and the second is an adult mouse in worn pelage that is impossible to allocate. The females are polyestrous in captivity, with an estrus cycle lasting about five days. In the wild, reproduction may cease in winter or at other unfavorable seasons. One to ten young, with an average of three or four, are born in a hairles, blind condition.
Growth is rapid and the babies are weaned at three to four weeks.
Females may enter their first estrus at this time, but the onset of reporductive activity usually occurs after five to six weeks. The litter size of the female increases with each birth, peaking at the fifth or sixth litter, and declines thereafter. The young animals may remain with the mother for some time after they are weaned. Literature Cited MacMahon, J. A. 1985. Alfred A. Knopf, New York, 559p.