Releasing orphaned field mice - Too cold?

[JudithD]

Hi,
I'm new to the forum and was hoping someone could help with a question.

My husband found a field mouse yesterday in his parking lot at work.

It is fully furred, eyes still closed. I have it on a heating pad and feeding a puppy milk supplement. He is eating well and passing urine and stools also.

Would anyone have an idea how old this mouse would be?

My most important question - I live in the North East region of the U.S. and it is already starting to get cold here. Night time temperatures are in the 40's.
Sorry, I don't know what that would be in Celsius.

Would he know how to survive if I released him when he seems ready? Do they need to find another mice colony to survive the freezing winter? Or would it be best to wait until the spring time when it turns warmer?
I'm just worried about releasing the little guy unprepared to deal with our bad winters.

Thank you for any answers... Judith

[valleyforge]

Hi Judith,

Good work so far ... raising an orphan mouse is quite a commitment to undertake.

If its eyes are not yet open then it is likely less than 12 days old, so should be fed every hour during daylight hours and every 2 hours overnight.

In addition to the milk replacer, you should also feed colostrum at least until they are weaned (at a ratio of one part colostrum to 3 parts milk replacer) ... your veterinarian or local wildlife rehabilitator should be able to help you resource that.

Mice should begin to wean around 9 days old, before the eyes are open, so you should try it with some moistened rusk, or breakfast cereal, or a small piece of apple, pear or banana too ... the sooner you can get it eating solids the better.

It would be unwise to release a young mouse now before spring, and you need to be aware that in raising an orphan of this age on its own, it is more than likely going to become imprinted on humans and so may not be suitable for release at all (not being equipped to bond with its own kind) ... so realistically, you may need to consider keeping it for the duration of its short lifetime ... in captivity it should survive between 18-24 months ... in the wild, average lifespan is probably closer to 2 months.

Good luck.

[posie]

Did you say 2 months ?

[JudithD]

Thank you....

So I should try solid foods in addition to the milk replacement formula?

This is my second mouse that I raised as an orphan. The first one I did keep, as it again, seemed too cold at the time to release. We kept her in a very large aquarium with various tunnels, a wheel to run on, etc.

She lived a long life - 7 years! But I felt terrible about keeping her alone in captivity and this is what I hoped to avoid.

Thank you again. Judith

[valleyforge]

Originally Posted by posie

Did you say 2 months ?

I'm afraid so. My response was based on the species Apodemus sylvaticus, which is what we in the UK recognize as a field mouse or wood mouse.

I'm not familiar with the species that is commonly referred to as a field mouse in New England ... though it's most probably be the Meadow Vole, Microtus pennsylvanicus ... but for the purpose of support of an orphan, the advice is similar.

My reference sources suggest that the Meadow Vole has only slightly greater longevity than our wood mouse, at average max of 154 days in the wild, and up to 3 years in captivity.

If Judith's previous charge survived for 7 years, then it was a remarkable animal indeed ... or some other species.

For Apodemus sylvaticus, mortality increases in Spring due to both avian and mammalian predation (when predators are hunting more to feed their own offspring) ... few adults will survive from one summer until the next. In captivity, the longest any wood mouse I have raised has survived has been 23 months.

[valleyforge]

Originally Posted by JudithD

So I should try solid foods in addition
to the milk replacement formula?

Yes ... try a variety of foodstuffs ... fruit as I previously suggested, plus lettuce leaf, dehusked sunflower seeds, and chopped (unsalted) nuts.

Originally Posted by JudithD

But I felt terrible about keeping her alone in captivity and this is what I hoped to avoid.

Orphans raised on their own rarely socialize with others of their kind when ready for release. If released into the territory of another field mouse, the dominant adults may well fight with and even kill strange adolescents, although younger individuals will generally be ignored. Once removed from their immediate family unit, successfully returning an orphan to the wild is full of problems.

Perhaps you should try contacting wildlife rehabilitators in your area to see if your mouse can be raised with other orphans of a similar age ... that way they all stand a much better chance of making it in the wild.

There is a list of Connecticut licenced rehabilitators listed here:
Southeastern Outdoors - Connecticut Wildlife Rehabilitators

[JudithD]

Originally Posted by valleyforge

If Judith's previous charge survived for 7 years, then it was a remarkable animal indeed ... or some other species.
(

You have my word, she was a mouse and she did live for 7 years.

I'll hopefully get a picture of the newest one and will post the link.

I don't know a lot about the behavior of wild mice, but does the mom throw them out of the nest at a certain age and if so, how do they survive on their own? Or do they live as a family?

Thank you for the link to wild life Rehabilitators, I'll look for some in my area.

[valleyforge]

In most families of rodents, the young males are more likely to disperse, usually leaving the natal area at between 1-2 months of age. Females often form close units outside of the breeding season, staying together for mutual warmth and protection.

Note that the list of rehabilitators is not a complete one ... just one I found easily on the internet. Your local veterinarian may know of other people in your immediate area, or contact your state wildlife department, or the National Wildlife Rehabilitators Association (NWRA) for further info:
www.nwrawildlife.org/

or the Connecticut Wildlife Rehabilitators Association at: http://www.cwrawildlife.org/
and : http://www.cwrawildlife.org/findarehabilitator.html

[JudithD]

Valley Forge,
Thanks again for all the information you have provided.

I didn't realize that they stayed with mom that long.

Obviously, mine thought differently..

What would make them go off on their own when they are not ready? His eyes are still closed and my husband found him in the parking lot at work..

Judith

[valleyforge]

He wouldn't have wandered off on his own ... he wouldn't be capable of that as yet ... even if the mother was killed and he and his siblings were starving.

He most likely was being transported by his mother from the old nest after it was disturbed ... perhaps by a predator, or perhaps due to the nest becoming flooded or damp. She would pick him up by the scruff of his neck and carry him that way. She'd have to carry each one of the brood to the new location before returning for the next one.

If the mother was disturbed by someone (maybe even your husband) or a car moving, or whatever, she may have had to put the little one down, in order to beat a hasty retreat for cover. She might not have been too far away when he was discovered.