The reproductive cycle in Belding ground squirrels was studied in the Sierra Nevada Mountains at two locations, one at 2,100 m elevation, the other at 3,000 m. Adults emerged from hibernation completely prepared physiologically for reproduction. Males tended to emerge slightly ahead of females and yearlings tended to emerge later than adults. Yearling females were fertile but produced smaller litters than adults, 4.48 vs. 6.31. Yearling males were infertile. They exhibited a slight seasonal cycle in testicular growth but did not reach sexual maturity. Testicular growth and spermatogenesis were incipient in many adults and in yearlings prior to hibernation.
Morton, Martin L. and Gallup, John S.
"Reproductive cycle of the Belding ground squirrel (Spermophilus beldingi beldingi): seasonal and age differences,"
Great Basin Naturalist: Vol. 35
, Article 10.
Available at: http://scholarsarchive.byu.edu/gbn/vol35/iss4/10