Reproductive biology, breeding seasons, and growth of eastern chipmunks, Tamias striatus (Rodentia: Sciuridae) in Canada.

Abstract

Reproductive, age, and body-size data from 1403 museum specimens from Manitoba to Nova Scotia and data on live chipmunks studied in the field in southeastern Ontario were analyzed. Schedules of the major stages of reproduction and growth are summarized graphically. Most adult males are in breeding condition (with large testes in black scrotal sacs and macroscopic tubules in caudae epididymidon) from March to June. As females can breed in March–April and (or) June–July, eastern chipmunks are unique among hibernating sciurids in that they have two breeding seasons per year. These occur over much of the Canadian range, with distinct waves of young appearing above ground in June and September. Spring breeding is probably annual and ubiquitous but records are too few to reveal the local frequency of summer breeding. Young have emerged in four consecutive Septembers at Stanley Corners, Ontario. Litter sizes from embryo and scar counts averaged 4.8 and 4.9. Although the young attain adult size and dentition in 3 months, most do not breed until 11 months old. We have questioned or explained conflicting reports and conclude that the breeding habits of Canadian chipmunks are essentially similar to those described by some U.S. workers.