Reproductive Rates and Cycles in the Pocket Gopher

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Abstract
About 2300 gophers (Thomomys bottae navus) were collected throughout the year from cultivated land in the Sacramento Valley, Calif., and examined for various indications of breeding. Year-long breeding occurs with peaks in fertility in spring, summer, and winter. Spring is the principal breeding season. Summer breeding is mainly by small-sized [female] [female] , possibly those born the preceding spring. Fertility is low during autumn. Winter breeding is variable. Size and position of testes are unreliable indicators of breeding. Testes tend to be smaller and scrotal during the hot summer period, larger and abdominal in winter. Testes in juveniles average relatively smaller than in adults, but undergo parallel size changes. Descent of testes may occur early in life, and they are frequently scrotal in juveniles. The average adult [female] is potentially capable of bearing more than 3 broods per year, but produces about 2. Estimates of litter size range between 4.92 and 5.77, mean number of fetal sites and of small embryos per female, respectively. Decrease in litter size with advance in pregnancy is attributed to fetal resorption. Fertility increases with size of [female] , but may decline in old age. Gophers in irrigated alfalfa fields are significantly more prolific during summer than those in non-irrigated lands, but no such difference was observed in spring when green forage was available to both groups. An effect of nutrition on breeding is indicated.

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