Every other Friday on Morning Edition NHPR’s Sam Evans-Brown tracks down answers to questions about the environment and outdoors for our listeners in a segment we call “Ask Sam.”
Sherry From Meredith asks: “I’m noticing a lot of chipmunks this year, as my son Josiah put it. Are we having a Chip-ocalypse? Like we had Squirrel-mageddon a couple of years ago?”
There were two crucial ingredients to the Squirrel-mageddon. The first was a year in which oaks and beech and other so-called mast trees produced a lot of nuts; what’s known as a mast year. The nuts lead to a boom in the squirrel population, but it was a basic fact of squirrel behavior that led to the roadkill: when they run out of food, squirrels have adapted to go looking for it.
“When they are in high density they expand, and this is when they can get killed by cars,” explains Mathilde Tissier who is a post-doctoral researcher participating in a long-term study on chipmunk populations (going on 16 years now!) up in Sherbrooke, Quebec.
Chipmunks don’t go roaming about when there’s not much food, because unlike squirrels — which live in trees and cache an acorn here and there, tucked between nooks and crannies of stonewalls or in the crevices of your house — chipmunks live underground and horde large amounts of nuts and seeds in those little burrows you see them skittering down into.
So when food is low, they go dormant.
“Chipmunks can do this, what we call a ‘lull,’” says Tissier, “They go inside the burrow in July when it’s really hot, and then they go out in late August and September.”
The adults, who have already been hoarding food all spring, will start to go underground. We’ll all probably start to notice fewer and fewer Chipmunks generally, as the summer progresses. The ones that will remain active — and which will likely get slowly picked off by predators, starve, or occasionally get hit by cars — are all the juveniles.
In the Northern US and Canada Chipmunks reproduce only once a year, but can time their reproduction to anticipate whether they expect it to be a mast year or not. If there’s a chance of mast, they can give birth later, so the juveniles head out on their own to forage in bountiful forests. If there’s no mast, such as this year, the young are born in the spring, so they might have all summer to attempt to build up a horde for the winter.
“We say Chipmunks are great gamblers,” explains Patrick Bergeron, who leads the long-term chipmunk population study.
So there will be a chip-ocalypse, and it’s the juveniles who will bear the brunt — the mast year baby boom. But because chipmunks remain confined to a relatively small territory, the drama will likely play out more in the woods and less on the roadways.
But where are the squirrels?
Now here’s a question I had: if we had a mast year last fall, why aren’t there tons of squirrels again, a la 2018?
I should add the caveat that it’s actually still possible that there is a bumper crop of squirrels out in the woods, but that they simply haven’t yet exhausted the supply of last year’s mast laying out in the woods, and haven’t started to go looking for food, and getting flattened by cars yet.
However, Patrick says it’s possible that the very reason we’re not seeing enough squirrels for a squirrel-mageddon might be because of all the chipmunks!
“If you look at the grey squirrels, they may rely on deciduous trees. So I see that they’re in a system that should be very similar to the chipmunks,” he says. This is called “interspecific competition". “And then in that race — or that arms race — of tracking the trees, I think the population maybe sometimes may fail to do so."
Just to restate this: maybe what happened was the population was a bit low, after all those roadkills in 2018, and so when we had another big mast year in 2019, who was there to capitalize on it?
Sam Evans-Brown, is host of NHPR’s Outside/In which you can subscribe to where-ever you get your podcasts. If you’d like to submit a question you can record it as a voice memo on your smartphone and send it to firstname.lastname@example.org, OR call the hotline, 1-844-GO-OTTER, OR submit it here.