Are you seeing more chipmunks than usual this year? Apparently there have been enough chipmunks to make the news, which caught the attention of the Masked Biologist. It is also the focus of this week’s wildlife matters.
As a feature writer, I spend one to two hours a day reading. I like to stay abreast of the news, and sometimes I am surprised by what I learn. In this case, back on July 18th, an article about chipmunks caught my eye first because Fox News used a stock photo of a rodent that was clearly not a chipmunk. I traced back to the AP wire, with the title “Chipmunks, fattened up on acorns, are driving people nuts.”
Now, I like a good pun as much as the next person, so I was compelled to read the article. Apparently in New England, there was such an abundance of chipmunks observed that it made national news. Now I don’t know if you have seen a preponderance of chipmunks this year, but I personally have seen more this year than in a couple years prior. As stated in the article, it is probably tied to last fall’s acorn crop. The oak tree in my yard dropped so many acorns that the chippies and squirrels couldn’t keep up. This spring there were still plenty covering the yard.
You probably know that squirrels take acorns and bury them in fall. They don’t remember where they buried every one, as the old wives tale suggests. Rather, they use their sense of smell to find them and dig them up in the spring. Chipmunks are different. They cache dry nuts and seeds in their dens to help them get through the winter. They have large complex dens, including a latrine and a food storage room or kitchen that can store as much as half a bushel of seeds and nuts. Chipmunks hibernate in the winter, but not like a bear does; they go inactive for long periods of time, especially when it gets cold, but they wake up and feed when they get hungry. So having a high quality cache of food is important coming out of the winter in prime condition.
So in order to have a bumper crop of chipmunks, we needed a bumper crop of acorns. But there is more to it than that. Here in the northern half of Wisconsin, we have two species of chipmunk, the gray (or eastern) chipmunk and the least (northern) chipmunk. Eastern tends to live in more deciduous environments, meaning trees that shed their leaves in fall. Northern prefers more coniferous areas, or areas with a lot of trees that produce cones. Early in the last century, northern was probably far more common in northern Wisconsin. Eastern moved in, though, and there were naturalists that predicted that eastern would completely displace northern in the north. Both species coexist readily, with plenty of resources and some separation of habitats, so depending on where you land in the Northwoods you may have one species or both.
An important difference between the two species in this context is reproduction. Both species breed in April and give birth about a month later. Eastern chippies, though, breed again in July-August, so they can have another litter of 4-5 babies in early fall, as the acorns are dropping. In years of less food, there might be more competition, and with chipmunks out looking for food during the day, more predation. That could lead to less breeding and the failure of the second litter. In a year like last year, though, with abundant acorns, the eastern chipmunk which as I said prefers deciduous forests like oak stands would have a full healthy litter, possibly up to 7 young, and there would be that many more chippies going into the winter. Then you add on a forgiving winter (in chipmunk terms, anyway) and a spring that’s right on time with plenty of leftover acorns, and you have the recipe for an explosion of the chipmunk population.
Now, if you are concerned that chippies will overtake the forest, don’t worry. As a rodent, chipmunks are near the bottom of the food chain, meaning lots of animals make chipmunks part of their diet. The predatory mammals and birds we have here in the Northwoods will take advantage of this plentiful food source and help keep the population in check.