By David Wasmuth

David Wasmuth is a local environmentalist and amateur naturalist. He is a Rutgers Environmental Steward and the founder of the Montclair Backyard Habitat Project. 

Amid the mix of disturbing and hopeful news that has made 2020 a year like none other, one quietly odd phenomenon has been hard to ignore: chipmunks seem to be everywhere. It sometimes feels hard to step outside without all but tripping over one. Have months of lock down heightened our awareness of something that was always present? Or will 2020 be remembered as, among other things, the year of the chipmunk?

In fact, the chipmunk boom is not just a matter of perception.  If you recall the more innocent days of fall, 2019, you may remember another unusual phenomenon: acorns. Everywhere. That now seemingly unremarkable year was distinctive in at least one way – it was a mast year for oaks.

Oak trees have a mysterious way of coordinating their acorn production. In some years, they produce relatively few acorns and in others almost none, causing a crash in chipmunk and squirrel populations. Then, in irregular intervals ranging between two and five years, come mast years when all the oaks in a region suddenly produce copious acorn crops. There is no sure explanation for how the trees work out this synchronization. Weather conditions are often cited, but there are also suggestions that the trees “talk” to each other using chemical signals.

From the trees’ point of view, this is a survival strategy. In a mast year, there are far more acorns than squirrels, chipmunks, and other animals can consume. They still bury or cache them for future use, but a lot don’t get eaten, allowing plenty of young oaks to sprout.

From a chipmunk’s point of view, this has been a boom time, a kind of chipmunk Roaring Twenties. Since last winter’s food caches were filled to overflowing, far more chipmunks than usual survived to reproduce in the spring. And in an especially food-rich year like this one, chipmunks will often bear a second litter in July, so we can expect to see a fresh crop of young ones leaving their mothers’ burrows around this time. What humans see either as the epitome of cuteness or as a garden pest, hawks, foxes, raccoons, and snakes see as a meal, making this a good time for predators, too. However, in the chipmunk world as in the human one, good times don’t last forever. Oaks rarely do two mast years in a row, so the booming chipmunk population of 2020 is likely to crash by next spring.

THE CHIPMUNK LIFESTYLE

Despite their adorable appearance and almost tame behavior around humans offering food, chipmunks are antisocial with others of their species.  Chip and Dale aside, they are not likely to get involved in bromances. They live miserly solitary lives, obsessively filling their caches with the nuts, seeds, and acorns they stuff into their cheeks. Since their half-acre ranges overlap, encounters with other chipmunks are common.  These lead to noisy squabbles, with burrow entrances especially fiercely defended.

For such a small animal – no more than ten inches, including tail – chipmunks excavate surprisingly large and complex burrows, using those expandable cheeks to carry out the dirt. Their tunnels are up to 30 feet long with two entrances and may include branching side tunnels.  About three feet below the surface, the chipmunk installs a leaf-lined nesting chamber and a food chamber capable of storing a hoard of up to half a bushel of provisions. In case that’s not enough, it may hide more caches outside the burrow.

Besides the vegan fare we associate with them, chipmunks will also eat insects, worms, baby mice, birds’ eggs, and baby birds, so a mast year is bad news for songbirds.

By late fall, the chipmunk will retreat into its burrow, seal the entrances, and hunker down for the winter. Its body temperature drops by about half, and it sleeps, waking occasionally for a snack from its cached food. In March, males emerge to visit the burrows of females in search of mates. As might be expected given chipmunk social skills, courtship can be contentious, but once the male has found an accepting female a few hours of affection ensue. Then he leaves. A litter of three to five is born a month later, and a month after that the young begin emerging from the burrow to forage with their mothers until they are ready to strike out on their own.

While chipmunks are normally not big on social life, there is one circumstance in which the community pulls together. When a predator is spotted, they will join in a chorus of chip sounds to raise the alarm; the chorus sounds different depending on whether the predator is a bird or a land animal. So, if you’re feeling disillusioned about Chip and Dale, you may find comfort in knowing there is a kernel of truth in Alvin.

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