Chipmunks also line their burrows with leaves, rocks, sticks, and other material, making the burrows even harder to see. "The vocal repertoire of the chipmunk consists of five more or less stereotyped sounds: the chip, the chuck, the trills, the whistle or squeal, and chatter." The chipmunks' trill has been measured to occur at the rate of 130 vibrations per minute. In a six-year study that tracked 59 resident and 49 transient chipmunks on a 1.5 acre study area in Spotsylvania County, Virginia during the late 1970s, chemistry professor Lawrence Wishner significantly contributed to contemporary published research regarding the Eastern Chipmunk's behavior by drawing on his copious, localized observational data. Wishner noted that "it cannot be overemphasized that the uniqueness of this study lies in its continuous day-to-day observation of 108 individual chipmunks for a period of six years." Diet The chipmunk is mainly active during the day, spending most of its day foraging. It prefers bulbs, seeds, fruits, nuts, green plants, mushrooms, insects, worms, and bird eggs. It commonly transports food in pouches in its cheeks. Lifecycle The eastern chipmunk defends its burrow and lives a solitary life, except during mating season. In fact, the chipmunk's solitary existence has been noted as "one of the most characteristic behavioral features of the chipmunk," whereas "social interaction of a relatively peaceful nature occurs only during the brief period of courtship and mating, and during the six to eight weeks that the young spend with the mother after birth." Females usually produce one or two litters of three to five young. The two breeding seasons are from February to April and from June to August. During the winter, the chipmunk may enter long periods of hibernation. Predators of the eastern chipmunk include hawks, owls, foxes, raccoons, snakes, weasels, coyotes, bobcats, lynx, domestic dogs and domestic cats. On average, eastern chipmunks live three or more years in the wild, but in captivity they may live as long as eight years. Eastern chipmunks are known to be one of many hosts for the parasitic larvae of Cuterebra botflies. T. s. doorsiensis The subspecies Tamias striatus doorsiensis was described in 1971. It is only found in Door, Kewaunee, northeastern Brown, and possibly Manitowoc counties in northeastern Wisconsin. Compared to the other subspecies of eastern chipmunk present in nearby in Michigan and Wisconsin, they have brighter patches behind their ears, grayer hair along their backs, and