Reproductive ecology of black-tailed prairie dogs (Cynomys ludovicianus) was studied on the Charles M. Russell National Wildlife Refuge in northeastern Montana (1978–1980 and 1985). Breeding took place from early March through early April in most years. Persistent snow cover and below normal temperatures in February and March of 1978 delayed the start of breeding. Litter size averaged 4.4 but varied significantly among years. Average yearly litter size was correlated (r2 = 0.986) with summer (June-September) precipitation prior to the breeding season. Largest average yearly litter size (5.0) followed record precipitation, while the smallest average yearly litter size (3.8) followed extreme drought. More than half the yearling females failed to breed while 88% of the females two years and older bred. Testes weights were greatest early in the breeding season and regressed rapidly during April.
Knowles, Craig J.
"Reproductive ecology of black-tailed prairie dogs in Montana,"
Great Basin Naturalist: Vol. 47
, Article 3.
Available at: http://scholarsarchive.byu.edu/gbn/vol47/iss2/3