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Columbian ground squirrel
It is difficult to characterize these animals by weight, as fat
storage for hibernation is a continual process throughout the summer
months. The total length of a Columbian ground squirrel ranges from
325-410mm, of which 80-116mm is tail. These ground squirrels have
stout bodies with short, dense fur. The nose and face are tawny. The
dorsum is a cinnamon-buff color with darker brown under fur. The eyes
are ringed with a line of pale buff. The legs and venter are buffy,
and the tail is black.
Reproduction
Breeding occurs during the early spring after these ground squirrels
awake from their winter hibernation. The testes of the males develop
during hibernation, and the squirrels are ready to mate shortly
after they emerge from their burrows. The females emerge about one
week after the males, and they ovulate shortly thereafter. As
females approach estrus, their genitals become swollen and emit an
odor most attractive to males of the species. Males locate females
by this odor. Unmated females return to estrus in two weeks.
The average litter size is 2.7 young, but there is a great deal of
variation. Litter size varies with both female size and elevation.
Females living at lower elevations give birth to larger litters than
conspecifics living at higher elevations. Similarly, larger females
bear larger litters than smaller females.
The young are altricial when born. They weigh approximately 6.8-11.4
grams at birth, but they develop quickly. They have hair by 3 days
of age, and they are able to walk and climb within 15 days.
Juveniles nurse for about 30 days, but they remain near their
mothers throughout the first winter of their lives.
Male Columbian ground squirrels reach sexual maturity at about three
years of age. Females may mate in their second season. Full adult
size for both males and females is reached in the third year of
life.
Behavior
Columbian ground squirrels are moderately social animals. They live
in fairly large colonies where related females maintain spatial
proximity. Population densities around 61 animals per hectare are
common.
Males emigrate from their natal ranges and establish residence among
groups of females that are unrelated to them. Females typically
remain in the colony in which they were born but occasionally may
emigrate to a new area.
These animals are active during the day and retreat into their
burrows during the night. Burrows can be elaborately constructed,
especially those used for hibernation. In the hibernaculum, a
squirrel builds a dome-shaped nest of finely shredded grasses.
Drainage holes are often excavated in the floor of the hibernaculum,
and these may prevent flooding during the fall and spring. Males
cache food within their hibernaculum for use in the early spring.
Since males typically emerge from hibernation well before plants
start growing, this food cache is very important to their survival.
Females, which do not emerge until the first shoots of grass are
poking through the soil, do not need such a storage system.
The size of the hibernaculum is related to the size of the animal
using it. Young animals excavate smaller chambers to be used for
hibernation than do adults. Immature animals often spend their first
winter in a hibernaculum close to their mother -- often a separate
chamber within the same burrow system. This may account for the
relatively high (87%) overwinter survival of juveniles.
These animals are active during the summer days, but their activity
level decreased throughout the summer. Males gain weight very
quickly after the mating season ends, and by the time the hottest
weather hits in July and August, these males are at risk of
overheating in the afternoon sun. Males enter hibernation much
earlier than do females, avoiding heat and water stress.
Females enter hibernation later than males, and the timing of entry
into hibernation is in part controlled by the timing of parturition.
Females cannot gain the weight necessary for hibernation until after
they have weaned their litters. Therefore, females giving birth late
in the season are among the last to enter into winter sleep.
Food Habits
These vegetarians eat flowers, seeds, fruits and bulbs. Among
preferred foods are dandelion, timothy, clover and yarrow. In
captivity they should be offered a complete diet of rodent lab blocks, and rat or mouse
mix, with bits of fruit or veggies regularly. Cheerios or wheat
bread are great treats, in small quantities. Do NOT feed chocolate,
fried foods, salted foods, candy or junk food! They may enjoy
crickets and mealworms if they are captive bred, never feed wild
insects as they may carry parasites. Vitamins, like Nutri-Cal are a good addition to their diet, and added calcium
during nursing and growth due to demands on their systems at those
times, but take care not to overdo it. Water bottles should be used
to proved constant, clean water. Ceramic or stoneware food dishes
work well for keeping seeds or fresh foods off the floor, and a wire
mesh hopper that allows them to eat the lab blocks through without
extra waste.
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