Breeding

If you are thinking of breeding your Chipmunks you must take into consideration a number of factors. Firstly the size of the cage, will it be large enough for a whole family of Chipmunks. Do you have the space to build a larger cage? Will you be selling the offspring and is there a potential market in your area? All these issues must be taken into account before you introduce a mating pair.

Choosing a mating pair
Ideally you should try not to breed a pair of Chipmunks that are closely related (inbreeding), such as ‘brother and sister' or ‘mother and son' or ‘father and daughter', as this may produce defects or deformity in the offspring. Ideally you should get one of the breeding pair from one source and find its mate from another; this is known as ‘out crossing' and should reduce the risk of any defects in the young.

Sexing your Chipmunks
It would be a good idea to confirm the sex of your mating pair just incase you have been given the wrong sex of Chipmunk. This can be easily checked if your Chipmunk is willing to turn up side down. They will do this quite happily throughout their daily activities, but you must try and get it to stay still long enough to view its rear end. You could try placing some food on the outside of the cage such as a piece of apple or a grape which they will happily cling on to the wire mesh while eating the treat, this will give you the opportunity to view the sex of the Chipmunk. In young animals, or in adults which are not yet ready to breed, a great deal relies on your judge of distances. With a female Chipmunk the distance between the urethra is very short, only about 5mm. With an adult male Chipmunk, the distance between the anus and the penis can be up to 20mm. In younger animals these distances are slightly less, but if you have one of each sex, you should be able to tell the difference.

Breeding groups
Chipmunks can be kept in breeding groups, but it states in numerous books to keep more females than males, for example, in a group of four Chipmunks you should have one male and three females, a group of six Chipmunks you should have two males and four females. This will help prevent fighting between males when the females come into season.

After watching and monitoring my colony of chipmunks over the last few years, I have found the females are the more aggressive of the two, this may be a contradiction to all the books you read, stating that the males will fight during the mating season. To be honest I have not really witnessed this myself, I have found the females will become very aggressive to each other once they are pregnant, this is probably due to the females wanting their own space ready for the new babies to arrive. Even after the babies are born the female will still be aggressive to the others, keeping the rest of the colony as far a way from her nest box as possible.

Reproduction
Chipmunks will mature and be ready to breed the following year after they were born. This will not matter if they were born early spring or late summer. Once the winter has been and gone and spring is upon us, the days will become longer, buds will begin to appear on the trees and the temperature will become warmer, the matured Chipmunk will be ready to mate.

Chipmunks kept indoors will probably start mating early spring, maybe around March, especially if they have not had a true hibernation period due to artificial light and indoor heating. Whereas Chipmunks kept outdoors will probably start around April / May for an early litter and July / August for a late litter depending on the climate. It is not advisable to mate your female Chipmunk too often, as pregnancy can take a lot out of her and you will only shorten her life span.

Once the female has come into season (on-heat) she will make it very known to everyone around her, although the males will probably know about it long before you do. During the ‘on-heat' period the ova (eggs) are released and the female will be receptive to a male, so that the eggs may be fertilised before they deteriorate. She will make her condition quite plain and will be calling for any male by chirping very loudly, you will not forget this sound once you have heard it the once, it sound a lot like a bird chirping extremely loud. She will continue chirping on and off throughout the day allowing any male that catches her to mate with her. She will mate with as many males as she feels like and may even harass any male who has lost interest in her. The female will only be ‘on-heat' for one day and the following day the female will have nothing to do with the males. Over the following week either the fertilised ova will implant into the uterine wall whereby pregnancy commences or the unfertilised ova will deteriorate and the cycle will start all over again. If she has not conceived this time, she will come into season again within the next ten to fourteen days, maybe up to twenty days with some females.

Pregnancy
After the first week or so of pregnancy, your chipmunk will show a slight enlargement towards the lower mammary glands, this is due to the influence of the progesterone in the blood stream. Not long after the twenty day mark the other glands further up the abdomen will become more noticeable, also there may be some widening of the animals girth. The babies will be carried in the horns of the uterus, not the in the body, which means for most of the pregnancy they will be tucked evenly up under the ribs, making it easier for the female to still climb and search for food. On her final week of pregnancy you may notice her belly becoming a little more flabby and the skin stretched causing the fur to appear thin. She will usually remain active throughout the pregnancy and may even become a little nasty to other chipmunks that she comes across while searching for food and nesting materials.

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