About Tamias amoenus J.A.Allen, 1890
Tamias amoenus has a dark reddish body color mixed with cinnamon. It has five longitudinal dark stripes that are either black or mixed black, separated by four lighter stripes. The outer pair of these pale stripes is narrower and creamy white, while the more centrally located pair is gray or smoke gray. Each side of the head has three dark stripes, with two lighter stripes between them, and the crown is black or smoke gray. Males and females have similar brain size, roughly equal tail length, ear length measured from the notch, and lower tooth row length. However, females are larger in most other body measurements. Average body mass varies: large males have an average weight of 49.7 g (1.75 oz), while large females average 53.5 g (1.89 oz). Male-biased size sexual dimorphism is common among mammals, but T. amoenus displays female-biased dimorphism. In areas where this species overlaps in range with the least chipmunk or red-tailed chipmunk, it may be difficult or impossible to tell the species apart in the field, and laboratory examination of skeletal structures may be required for identification. Both sexes of T. amoenus have genital bones: males have a baculum, and females have a baubellum. After hibernation, one annual breeding event occurs in late April to early May. At this time, male testes are enlarged, a change supported by warmer temperatures; females also show enlargement of their ovaries and uteri. Females are in estrus for one day, and they produce vocalizations 3 to 5 days before estrus. These vocalizations alert males to their reproductive readiness and trigger intrasexual selection among males. Females mate with one or more of the males that come to her den. The average litter size is around four or five, and births occur in late May to early June. Young in litters of six are smaller, which indicates physical constraints on the mother. The lactation period lasts approximately 2 months, and by the beginning of September, the young reach a size comparable to other individuals in the population. Female reproductive success has been observed to be significantly related to body size, while male reproductive success is independent of body size.
