Reproduction and emergence of juveniles in Tamias straiatus (Rodentia: Sciuridae) at two localities in Ontario, Canada

Eastern chipmunks (Tamias striatus) were studied in Algonquin Park in 1968 and at Chaffey's Lock, Ontario, in 1969 and 1970, employing a combination of trapping, marking, and systematic observation. Spring breeding occurred in all years. No summer breeding was observed in 1968. In the summer of 1969, only one of 10 females was pregnant and no young were seen. In 1970, seven of nine adult females as well as a female born in the spring had litters in the autumn. At least five females bred in both spring and summer. Apparently, the incidence and extent of summer breeding is variable in these local populations. Females bred toward the end of March and, when polyoestrus occurred, again in June or July. Young were born most commonly in April and August. In the summer of 1970, 22 young first emerged from their burrows at between 5 and 7 weeks of age. Estimated weights at emergence varied from 27.9 to 70.9 grams and averaged 50.5 grams. At emergence, average litter size for a breeding period varied from 2.8 to 5.3.