Breeding Seasons and Fecundity of Female Gray Squirrels in Ohio

Abstract

Measures of productivity, breeding seasons, and fecundity of female gray squirrels (Sciurus carolinensis) were studied in southeast Ohio between 1966 and 1970. The corpus luteum begins to decline in size before birth and disappears 5-7 weeks postpartum. Placental scars are visible at least seven months postpartum and, if uteri are chemically treated at scar sites, can be separated into winter-spring and summer-fall implantations. Breeding extended from late December until September, with peaks in breeding activity occurring 2 to 25 January and 19 May to 18 June. Ovum and embryo mortality totalled 9.0 percent for 33 pregnancies. Summer-born juveniles averaged 68.1 percent mortality between implantation and the hunting season in midfall, whereas spring-born juveniles averaged only 15.9 percent mortality over a similar period, which is 3 to 5 months longer for spring-born young. During the January-September breeding period, an average of 2.2 percent of the subadult females, 55.8 percent of the yearling females, and 95.4 percent of the adult females had at least one estrus cycle. Placental scar counts were significantly higher in adult breeders compared with yearlings and in summer-breeding adults compared with spring-breeding adults. During 1968-70, 60.9 percent of the adult females bred in winter-spring, 66.4 percent in June-August, and 27.3 percent during both periods. A representative group of 100 gray squirrels of both sexes could implant 110 embryos during a single January-September breeding period. J. WILDL. MANAGE. 39(2):426-438 Both gray and fox (S. niger) squirrels are important game animals in Ohio; in 1962, it was estimated that 306,331 Ohio hunters killed 1,428,876 squirrels (Donohoe 1965:73). Squirrel hunting ranks second only to cottontail rabbit (Sylvilagus floridanus) hunting in Ohio. Estimates of natality are needed for both species of squirrels to better assess the effects of various levels of mortality, particularly mortality induced by hunting, on population maintenance. This paper deals only with the gray squirrel, which contributes 79 percent of the squirrel harvest in the unglaciated portion of eastern Ohio (Donohoe 1965:76). The objectives of this study were to delineate the annual breeding season, to determine the effects of age and season of breeding on the fecundity of the female gray squirrel, and to determine the reliability of using corpora lutea and placental scar counts as measures of productivity of the gray squirrel in southeast Ohio.