Backyard birders, gardeners and others across Pennsylvania have been wondering if it’s just them or have others noticed a marked uptick in chipmunk and squirrel activity this year.
Well, it’s not just your backyard. The rodents are more numerous and correspondingly more active, and perhaps more damaging in the garden, this year.
“This is what I would call a peak year for rodents, particularly rodents that rely on hard mast like acorns,” commented Carolyn Mahan, a Penn State Altoona researcher in behavioral ecology of sciurids, which are members of the squirrel family.
She noted that researchers at the Institute of Ecosystem Studies in Millbrook, New York, in 2006 determined that numbers of acorn-dependent rodents, like white-footed mice and chipmunks, will peak about two years after a good mast crop.
Mahan explained that an abundant mast crop leads to a higher winter survival rate of the rodents, which then leads to increased reproduction, but “there will be a year when there’s not a good mast crop. Then there will be a crash.”
According to the Pennsylvania Game Commission, many parts of the state experienced an abundant mast crop in 2018.
“Normally when we look at long-term data, we see peaks and valleys for almost any animal,” Mahan said. “You can trace it back to availability of food resources.
Even with the abundance of backyard bird feeders, the cyclical boom and bust can be seen in animals like chipmunks and squirrels, which will make more use of resources offered by human when scarcity strikes the neighboring woodlands.
She noted that chipmunks are highly territorial and will tolerate other chipmunks only at a common food source, but also are quick to move into territory, including the extensive burrow system, of any other chipmunk that’s removed from the scene by something like a cat or hawk.
“We call them floaters,” she explained of the chipmunks that occupy spots vacated by other chipmunks.
In contrast, gray squirrels form loose social groups, usually among related individuals, and those groups increase when the population grows.
And, as the chipmunk and squirrel populations responded to mast abundance, predators of the rodents, such as Cooper’s hawks, gray foxes and great horned owls likely have increased in response to the chipmunk and squirrel boom, Mahan said.
According to the Game Commission, both chipmunks and gray squirrels live two to three years in the wild, longer in captivity.
Female chipmunks give birth to one to eight babies, usually four or five, in mid-April through mid-May, and often a second litter in July or August. Female gray squirrels give birth to litters of four or five young in late February through early April and often a second litter in July or August.
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Contact Marcus Schneck at mschneck@pennlive.com.
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