Photoperiod and Reproduction in Flying Squirrels, Glaucomys Volans

In Michigan and Massachusetts, flying squirrels, Glaucomys volans, have two peaks in breeding activity; the first peak in the number of litters is in April and the second in August. All 19 males examined from March through July had scrotal testes, but only two of eight from August through November and five of 12 from December through February. Experimental data indicate that long photoperiods, beginning in September, inhibited testicular descent during the normal breeding season. The normal, seasonal reproductive cycle was maintained in the absence of temperature cues. Testicular descent in males was hastened with accelerated decreases in photoperiod. Reproduction was induced 6 months out of phase when animals were exposed to photoperiods 6 months out of phase with the seasons.