Koprowski, J. L. 1992. Removal of copulatory plugs by female tree squirrels. Journal of Mammalogy 73(3): 572-576.
Copulatory plugs form in the vagina of females from the semen of male fox squirrels (Sciurus niger) and eastern gray squirrels (S. carolinensis). Plugs are opaque white with waxy to rubbery consistency resembling those of other rodents. Although copulatory plugs frequently are hypothesized to prevent the successful copulation of subsequent males, female tree squirrels often remove the plug within 30 s of copulating and either discard or consume it. The removal by the female of a copulatory plug suggests that conflict may exist between the reproductive strategies of the sexes.