Wednesday, November 4, 2020

A Circus of Chipmunks

A "circus of chipmunks" proposed as a venery term
To anyone spending any time outside, this has been the year of the chipmunk. Yards and gardens are punctuated by holes about the size of a silver dollar. Under bird feeders, along the Rail Trail, these striped critters are always scurrying, scurrying, scurrying. The name “chipmunk” is derived from Native American “jidmoonh,” from the Odawa tribes that lived in the Great Lakes region. The Anglicized “chip” refers to the high-pitched “chip-chip-chip” alarm call made when a possible predator (fox, cat, dog, human) is seen.  

Chipmunks are rodents, albeit cuter than rats. Within the species family Sciuridae (squirrel) there is a division between tree squirrels and ground squirrels, the latter including not just chipmunks but also prairie dogs and groundhogs. Massachusetts is host to the Eastern chipmunk. Out west there are 23 chipmunk species – all not to different visually from the Eastern – but genetically different enough to not interbreed. There is one more species, the Siberian chipmunk, in northeast Asia, which has become an invasive species in western Europe via escapees from the pet trade. There is a strong resemblance across all of the species: brown, striped, furry tail and cheek pouches in which to stash food so that it can be brought back to the nest.

Eat and be eaten: Chipmunks are omnivorous. Their diet is primarily seeds, nuts, berries, fruits and the tender plant shoots and buds, but also insects, worms and the occasional bird egg. Same for squirrels. Chipmunks can be garden pests and wreak havoc on bulb plantings. Unlike squirrels, which scatter-bury acorns for digging up later, chipmunks bring nuts and seeds back to their nests. There, along the 10-20 feet of tunneling, they will have a larder of food set aside for winter consumption. The burrows extend below the frost line.

Chipmunks utilize an intermittent hibernating state. From a body temperature close to 100F degrees and a heart rate of 200-300 beats per minute, body temperature approaches 40F degrees and heart rate to 10 bpm. Every few days the chipmunks rewarm to normal temperature, become active, eat, and then cool down again. The net effect is less food needed to survive winter, and for the females, more body fat reserves for a successful spring pregnancy.

As to what eats chipmunks, think hawks, feral and pet cats, weasels, foxes, coyotes, snakes… As chipmunks’ diurnal lifestyle can extend to near-dawn and -dusk hours, they can also fall prey to owls. Great blue herons have been known to stalk near bird feeders for the foraging chipmunk, oft times dipping the struggling animal into a birdbath or other water before swallowing it whole.

As to why this was the year of the chipmunk, last year was the year of the acorn. Last year’s abundance of food carried over into this year, allowing for larger litters and better survival from the spring and summer pregnancies. The young, who at birth are hairless, blind and about the size of a small bumblebee, emerge from the burrow after about six weeks and strike out on their own two weeks later. With the exception of mating, chipmunks leave solitary lives; males have no part in raising infants. In normal times, population density is roughly 1-2 per acre. In good years, this can increase five-fold.

The abundance of acorns in 2019 occurred because oaks do not produce the same yield every year. Evolution research posits that a same-sized crop every year will support stable populations of acorn eaters, which includes chipmunks, squirrels, woodchucks, skunks, turkeys and deer. By producing a large crop every other or third year, populations of seed-eaters are curtailed, and a greater portion of seeds will remain uneaten in good years. The key to this strategy is coordination—it works only if trees of the same species do it at the same time. How tree species coordinate is still somewhat of a mystery, but this synchronicity is probably aided by some combination of chemical signals passed through the air or through underground root/fungal connections. Regardless, this year’s chipmunk (and squirrel) population explosions were newsworthy across New England.

We say a “pride of lions, gaggle of geese, school of fish,” but why? As it turns out, social standing among Medieval European nobility required that men knew their venery – the proper naming of groups of animals – else be taken for crass and uneducated. Collections of these “terms of venery” culminated in a master list compiled in The Book of St. Albans, in 1486. Thus, we have a “colony of ants, a pack of wolves, a murder of crows,” and so on. A group of squirrels is a scurry. Sadly, a group of chipmunks is also a scurry, which lacks the alliterative appeal of a “scurry of squirrels.” Chipmunks are not native to Europe, which perhaps explains the lack of a better venery term.


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