Mating occurs from February to April and then again from June to July. The first litter of young are born around April and May and the second litter about July or August.
The average life span of a chipmunk in the wild is two to three years. Captive chipmunks have been known to live for eight years.
The females are usually chased by a number of males who want to mate. The males follow the females in a line and fight among themselves to see who can get closest to them. If the female chipmunks are not ready for mating they can be quite aggressive and will turn and chase the males away.
They sometimes attack the males who are following too closely. The females eventually become receptive (ready to mate). Usually the strongest, most dominant male chipmunks get to mate with the females.
Mating lasts for about one or two minutes, and then the females and males stay together for a short time. The females then chase the males away.
After a gestation period of about 31 days, the young chipmunks are born. During this time, the females carry leaves and grasses to their underground dens. The underground home has a large room or chamber that is used as a nesting site.
At birth, the baby chipmunks are pink and hairless. They weigh only three grams, which is the same as about three paper clips. The babies are about half an inch long and their eyes remain closed for about one month. The average size of the litter is four but this varies.
By the age of three weeks, the young are fully furred and by the time they are five to six weeks old they begin to appear above the ground.
When the baby chipmunks first come out of their den, they explore the ground near the entrance. Their mothers keep a close watch on them. The mothers and the babies remain together for about three months and then begin to separate.
The young must quickly find new homes. Most of them try to find empty burrows close to where they were born. The other chipmunks in the area make a chip-chip-chip sound. This lets the young know which areas or territories are already taken. Some of the young must travel to new areas to locate a home.
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