Deer Mice!

Steve Blight | May 20, 2015

My morning routine had become familiar. I got up, changed the water for the dog, and went down into the basement to check the live mouse traps. Sure enough, the little trap door on one of the black plastic boxes was closed, meaning that I had caught another mouse. Sighing and picking up the mouse trap, I went out to the garage where I unceremoniously plopped the lively but no doubt unhappy mouse into an empty 5 gallon pail – the mouse’s temporary holding pen until I was ready to make my all-too-frequent trip to deliver yet another mouse to an uninhabited place.

Deer Mice and their look-alike cousins, White-footed Mice, are extremely common and may be the most common mammal in Ontario. Based on my recent records, they are the most common mammalian visitor to our house. The range of Deer Mice is the entire province of Ontario, whereas the White-footed Mouse is only found south of Algonquin Park.

Deer Mice are highly adaptable little creatures, able to thrive in a wide variety of habitats – forests, grasslands, brushy areas – and buildings. They are omnivorous opportunists that eat seeds, fruits, insects, birds’ eggs, and a variety of other tasty items depending on what is available. They often forage on the ground, but regularly climb trees and shrubs to find food. They den in many different situations – in hollow tree branches, in wood piles or hollow logs, or on the ground in grassy nests. My evidence suggests they have a real fondness for pink fiberglass insulation as nesting material.

These little rodents can be extremely productive. The female is ready to breed at the ripe old age of 35 days, and on average will give birth to 4-5 young per litter. Mice breed in all four seasons and can have multiple litters per year. Were it not for the fact that so many other creatures prey on them, the world would soon be knee deep in mice. For example, the tiny skulls of deer mice are often found in the regurgitated pellets of owls, a testament to their importance in the food web. Foxes, coyotes, other birds of prey, snakes and members of the weasel family are all major predators of mice.

In the fall of 2013, there was a bumper crop of Sugar Maple seeds in our area. People noticed the number of mice seemed to be much higher during the fall-winter of 2013-14. This makes sense, as populations of wildlife often increase or decrease based on food supplies. And as the populations of mice rise and fall, so do the numbers of predators that take advantage of the population swings in prey.

Unlike some folks, I find deer mice quite cute. Their big black eyes, dainty nose and long whiskers remind me of pet hamsters I had as a child, and I have trouble disliking them. However, I don’t want them in my house, and I have spent hours combing the outside of the house looking for tiny gaps (as small as less than ½ inch wide) where they can get in. After what seems like having stuffed bushels of steel wool into cracks and gaps, the flow of mice into the house has slowed. However, I am still greeted some mornings by a closed trap door, meaning that I still have work to do.

In the beginning of our mouse battles, we were only taking the mice to the end of our driveway before letting them go. I figured that an animal that small would not have to be moved very far for it to never come back. However I have since learned that Deer Mice can find their way back to their home territories from quite a distance. According to one study I read, more than 50% of mice that had been trapped, marked and released 1.5 kilometers away made it back to their spot of capture within a day or two, including somehow crossing a significant river. There are theories on how they do this, but the answers are far from clear. As a result of this amazing new information, I now take my captures WAY down the road to an area where there are no houses for more than 2 kilometers in any direction before releasing them to fend for themselves. While I find Deer Mice attractive in a cute kind of way, I do not want them to come back to my house, thank you very much!

Observations: Fellow columnist Lorraine Julien sent her own story on mice: "My brother has an older cottage and they were inundated with mice up until they were able to seal it properly. I remember one winter going there and opening up the pantry. On the shelf was a very large glass jar with a plastic lid. The jar contained cooking oil. When I opened the cupboard door, all I could see were mouse faces looking through the glass!!! They had chewed through the lid and, one by one, they dropped into the oil and drowned. I think my brother said there were about 13 of them. I don't know, as I ran out of the cottage. I would sooner run into a bear than mice."