If you’ve been spending any time hiking this summer, walking through the woods or even just driving along Vermont roads, you wouldn’t be alone in thinking: Are there chipmunks, like, everywhere this year?
We turn to a small mammal biologist for answers.
It's been a good year for chipmunks in the northeastern U.S. A really good year.
“Yeah, there are quite a few additional chipmunks this year,” says biologist Bill Kilpatrick dryly. Kilpatrick is a professor emeritus at the University of Vermont and the author of the Vermont Small Mammals Atlas. He says the good year for the chipmunks actually started last year, when there was a bumper crop of beechnuts and acorns and other mast. The chipmunks were able to hoard their nuts, as chipmunks are wont to do, giving them a head start going into hibernation.
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“And so,” Kilpatrick explains, “as they were arousing during the winter they found that they had an abundance of food. That meant that they actually arose from hibernation earlier in the year and they also then had very high survivorship of their first litter of young.”
And if you think you're seeing a lot of chipmunks now, just wait. Chipmunks have the ability to control their reproductive cycles in abundant food years to have a second litter right about now.
Remember back to your lessons about the food chain and it likely won't surprise you to hear that chipmunk predators, like owls, are also likely to do pretty well this summer and fall.
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Says Kilpatrick, “There will be increased numbers of predators, not only bird predators but also things like weasels and foxes will also increase. And chipmunks are omnivores, so they're going to feed on other prey items like songbirds, like songbird eggs, like frogs. That makes up a portion of their diet as well.”
But the real winner in this boom and bust cycle might actually be the trees. Kilpatrick says the trees themselves have a strategy to actually kill off some of their predators.
"They use a strategy of trying to produce a lot of mast and then the following year produce very low mast so that the predators on those seeds essentially starve to death and are not there." - Bill Kilpatrick, University of Vermont
“They use a strategy of trying to produce a lot of mast and then the following year produce very low mast so that the predators on those seeds essentially starve to death and are not there. So they're playing the game kind of like the wildebeests on the Serengeti, producing all their seeds or all their young at one time so that the predators, in this case the seed predators, just can't feed on all of them and many of them survive to produce new trees.”
Now, you may remember a superabundance of other rodents, squirrels, in 2018. That was another big mast year, but Kilpatrick hypothesizes that the difference between a squirrel-pocalypse and a chipmunk invasion is in how they live: “It probably has to do with very subtle things about the difference in the reproductive strategy. The chipmunks are underground whereas the grey squirrels are up in trees in hollows in the trees and hollows in the logs. So with climate conditions maybe chipmunks had a real head start this year over grey squirrels.”
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As for why all the chipmunks in northern New England seem to want to run directly in front of your car, Kilpatrick has a theory about that, too.
“I think because there's just so many of them,” he laughs. “And they're trying to establish their own areas and they're many times they're chasing each other. We see a lot of interactions with chipmunks chasing each other and running right in front of cars.”
Other Vermonters are telling Vermont Edition that the chipmunks have invaded their gardens, crawled up inside their cars, and found refuge in their houses. But people who enjoy the antics of these chubby-cheeked mammals are enjoying the uptick in the chipmunk population while they can.
Broadcast live on Thursday, July 2, 2020 at noon; rebroadcast at 7 p.m.
