Mouse in the house
Mouse tackling a zucchini (press play to view)
Mice are the opposite of the old saying that children should be seen but not heard. They are more often heard but not seen. Yet, evidence of their presence is commonplace in the form of tiny footprints, tooth marks, and (EEK!) mouse droppings.
To be a mouse
Depending upon the species, female mice can become pregnant by 6 weeks of age, producing litters of 6-8 pups 5-10 times a year. If she lives the typical 1-2 years in the wild, she might produce over 100 offspring. That’s a lot of mice! Of course, mice suffer very high mortality rates – they are are food for many other animals such as owls, foxes, weasels, to name a few – so most of those offspring don’t survive for long.
Most mice are polygamous, that is, they have multiple mates, although females tend to be more monogamous than males. Nevertheless, it goes without saying that Mickey and Minnie Mouse are clearly exceptions to the rule.
Mice are experts at nest building and storing food in caches where one might least expect it, like in my tractor, boots, and chest of drawers. Cached food tends to be nonperishable, such as acorns or other nuts and seeds, however, mice are omnivores, eating beetles, spiders, bird eggs, plants, and even other mice when under duress.
As much as humans would deny it, mice have some characteristics we admire.
They are very social animals with a “nuclear family” – consisting of a mother and young littermates – expanding to a larger social group as the pups age, including older littermates, other relatives, and perhaps a dominant male. A parent typically accompanies a pup on its early forays out into the world. After all, who lets their child cross the street unattended?
Additionally, mice are highly opportunistic and skillful in taking advantage of their environment and making more mice. “Go forth and multiply” should hang on a plaque in all mouse nests.
Home Sweet Home
A typical house mouse has a home range of several square meters if they live in a human structure with access to food or up to thousands of square meters in the wild. Mice, particularly dominant males, will aggressively defend an established territory against unfamiliar mice and chase them away.
When a young male mouse matures, he is faced with a choice – remain and fight with dad to become dominant (à la Oedipus, who killed his father and married his mother) or emigrate to try to establish his own territory. Emigration is chosen more often than not. Unlike Oedipus’s mother, female mice are able to recognize closely-related kin by the smell of their urine and minimize inbreeding.
Can you hear me now?
Look in the mirror?
A seminal, if disturbing, 1973 study by John Calhoun looked at the population growth and behavior of mice in a mouse Eden.
In reality, Eden rapidly descended into a mouse dystopia. Initially, four pairs of mice were provided with endless food and water in a 70-square-foot “universe.”11 After a short get-to-know-each-other period, the mouse population doubled every 54 days during a honeymoon phase, and within 315 days reached 620 mice. If the mouse Eden had continued unchecked, more than 8,000 mice would be produced after 1.5 years.
Mice are social animals, yet the utopia began to deteriorate after 315 days. In the confined space, juvenile males were unable to emigrate, and those who failed to attain dominance – remember that the juvenile male’s options are to emigrate or to fight for dominance – congregated in an asocial group in the center of the space. Maternal abandonment of pups also increased at this time.
No pups survived after day 600, and reproduction virtually ceased after day 920 despite nearly 2,000 mice remaining. After 1,446 days the population had crashed to 120 mice and was projected to be zero after 1,780 days, despite plentiful food, water, and a reduced population. Perhaps most disquieting is the finding that when individuals from this mouse dystopia were removed and housed with mice raised under “normal” conditions, the dystopic mice were unable to regain normal social and reproductive behavior.
“You’d never let the darkness get the best of you.” - Mickey Mouse
Cats have mice to thank
Mice like house mice weren’t always the global animals that they are today. Prior to the development of relatively large, sedentary, hunter-gatherer settlements 10,000-15,000 years ago, mice and humans traveled in different social circles. Mice probably considered humans to be large mammals, best avoided. But once humans stayed in one place and began storing food, an arms race began between Homo sapiens and tiny Mus musculus as mice embarked upon millennia of pilfering from humans. Mice ultimately hitched rides with humans as they traveled along trade routes or even on boats to remote islands which were otherwise mammal-free.13
Enter the cat. Archaeological evidence suggests that humans responded to the ascendency of mice with a cry for help from cats, who are consummate mousers, as early as 11,000 years ago. And so the domestication of the cat began.
Take the good with the bad
If only we had remained as hunter-gatherers and never stayed in one place storing food, perhaps we would have a better relationship with mice – they might be considered as an occasional meal rather than as pests. We would worry less about diseases like Lyme, leptospirosis, and hantavirus, to name a few. That would also mean nomadic living with no cell phones, no cars, and no fast food (and no global warming).
Face it, mice are here to stay, and I prefer to admire their fascinating behavior and biology – albeit not too intimately! – rather than demonize them. So, go forth and make peace with a mouse.
1 “Mouse” is a catch-all term which can include the house mouse, Mus musculus, the white-footed mouse, Peromyscus leucopus, the deer mouse, Peromyscus maniculatus, and meadow mice or voles.
2 For example, see The Great Mouse Detective, the Redwall fantasy series, Mickey Mouse and his friends in many cartoons, and the classic Mighty Mouse cartoon. I still remember the Mighty Mouse theme song, “Here I come to save the day!”
3 Curious about the mouse who visited our counter every nice, I set up a GoPro camera, offered up a sacrificial zucchini, and discovered the impressive fitness skills of this particular mouse.
5 Some of the newer generation rodenticides have no antidote. As a veterinarian I find that infuriating!
6 Crepuscular animals are most active at twilight.
7 See the essay on animals’ eyeshine: https://forestbarkdollweil.com/night-eyes/
8 See the essay on porcupines: https://forestbarkdollweil.com/porcupines-and-their-quills/
9 If you are over 50 years of age you may not hear over 10,000-12,000 hertz. Sadly I have a hard time hearing the soft, high frequencies of the golden-crowned kinglets’ song.
10 Cochlea comes from Latin meaning “snail” due to its shape.
11 Calhoun uses the term “universe” to describe the space, which, from the size of mice’s home ranges described previously, hints at problems to come.
12 It is difficult to draw direct parallels to us from these observations. The relevance of much rodent research to humans might be similarly questioned but that is a topic for another essay.
13 Mice and other mammals who traveled with humans to mammal-free islands have caused extinctions of various birds and reptiles.
Special thanks to Zoe Weil’s editorial expertise