I recently hosted a party at which I was able to spend some time with my friend Kyle. We talked about the stacking of firewood and the general battening down of the hatches that occurs at this time of year.
Eventually our discussion turned to the fascinating topic of mice (my parties are amazing) and I thought this would make a perfect topic for a column. So Kyle, this one’s for you.
For most of us, the local wild mice are white-footed mice (Peromyscus leucopus). Both males and females maintain home ranges that vary in size from one half of an acre to one-tenth of an acre respectively. The size of the home range is directly related to the availability of food. Within their home ranges, each mouse will establish a smaller territory that it will defend against all other mice. And somewhere in its territory a mouse will build its nest.
The nest is usually built of plant material that is wedged into a tight crevice in rocks, trees, or (where I often find them) in piles of firewood. Occasionally, a mouse may even use an abandoned bird nest. The bird nest is usually left intact with a “roof” of grasses and twigs added to the top.
Male white-footed mice don’t really have to do much more than take care of themselves and find female mice that aren’t already pregnant. After mating, the males have no other family responsibilities, but the constant search for females puts them at a high risk of getting caught by a predator.
Females, on the other hand, have to raise offspring, which requires a great deal of effort. After a gestation period of only 23 days, female white-footed mice give birth to three to five tiny babies — naked, blind, and entirely dependent on their mothers for survival. To produce sufficient milk for her offspring, a female will have to consume up to three times as much food as a male mouse.
This is when the quality of a female’s home range is put to the test. If she picked an area with sufficient food, then everything will be fine. If she has to work too hard to find food, however, she exposes herself and her babies to an increase in the already high risk of predation.
Baby mice grow quickly and in less than a month they are ready to venture out into the world. Adults are mildly tolerant of the new youngsters, but by the time male white-footed mice are 10 weeks old they have already established territories and are ready to breed.
The breeding season of the white-footed mouse extends from February to October, with babies being born from March to November. In that time, a female may have up to four litters, which translates into 20 babies a year.
This may seem like a high number, but when you consider the predation rate faced by mice, it’s easier to understand. Weasels, snakes, hawks, kestrels, owls, foxes, coyotes, and even large frogs will eat white-footed mice, which occupy an important place in the ecological food webs of fields and forests.
As winter gets closer and the temperatures continue to fall, it is quite likely that mice will explore our garages and workshops in their never-ending quest for food and shelter. They may cause some trouble in the process, but they are simply looking for a way to survive in a rather unfriendly world in which they represent food for almost every local predator.
Bill Danielson is a professional nature photographer and author living in Altamont. Contact him at www.speakingofnature.com.