Observations of reproductive behavior, growth and development of the young, food habits, habitat preference, and daily and seasonal activity patterns of the Colorado chipmunk are presented for the first time. The breeding cycle is as follows: mating occurs in late February or early March; the young are born in early to mid-April and first appear above ground in May, but do not reach breeding age until the following spring. There is only one litter of young per year. The mean number per litter was 5.7 for three litters born in captivity. The sex ratio of the animals born in captivity and animals observed in the field was 1:1. The average weight at birth was 3.05 g and the daily increase in weight was 0.52 grams for 90 days. The eyes were opened 29 to 33 days after birth. The pinnae unfolded in 2 to 3 days and the auditory meatuses opened when 28 to 29 days old. The eruption of the teeth were as follows: the lower incisors appeared in 10 to 12 days, the upper incisors in 20 to 22 days, and the cheek teeth appeared in 34 to 37 days. The dorsal dark and white stripes appeared in 10 days. Colorado chipmunks at Arches National Monument are found in association with juniper-pinyon areas along solid rock ledges with tumbled rock masses at their bases and on higher ridges and ravines where the soil is rocky, and to some extent associated with the blackbrush and Indian rice grass of sandy flats near juniper-pinyon areas. The seeds or fruits of the following plants were most often eaten: Indian rice grass (Oryzopsis hymenoides), Russian thistle (Salsola kali), squawberry (Rhus trilobata), cliff rose (Cowania mexicana), and juniper (Juniperus osteosperma). The chipmunks do not become active until after sunrise and as the temperature increases to its midday maximum the activity of the animals decrease to a midday minimum. The chipmunks are inactive above ground from late November until late February. It is suggested that during this period the chipmunks alternate between sleeping and feeding from their food stores. Juvenile Colorado chipmunks molt twice during their first year and it is suggested that the adults also molt twice each year. The molt proceeds anterior to posterior in June and July and progresses posterior to anterior in the September-October molt.



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Life Sciences; Plant and Wildlife Sciences



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