I haven’t featured a wild mammal here in quite a while (white horses and new pets count as mammals but it’s a long time since they’ve been wild). Certainly the last wild mammal I remember writing about was the opossum that visited my parents’ feeders last winter. Perhaps not coincidentally, today’s critter has also been coming to our feeders. That’s the whole point of feeders, after all – to draw the animals to you, so you don’t have to go looking for them.
Generally the target group for feeders is birds, but rodents are big fans of the seed put out, as well. Squirrels get most of the attention, but chipmunks are just as frequently seen. In fact, when we first put our feeders out, the chipmunks found the seed within a couple days, but it took a few weeks before we saw the first squirrel there. Chipmunks are abundant in this neck of the woods. My parents have lots of chipmunks around, but up here we seem to have LOTS of chipmunks around.
The Eastern Chipmunk (Tamias striatus) is a forest species preferring deciduous and mixed woodlands, though urban parks will quite readily do as long as there are sufficient mature trees for food. It’s the only species of chipmunk (members of the genus Tamias) found in eastern North America. There’s one species that occurs in Eurasia, and the remaining 23 of the 25 species of Tamias are all native to western North America.
The Eastern Chipmunk’s scientific name, T. striatus, reflects its strongly striped back. It’s often described as having nine stripes, or five dark stripes interspersed with light ones, and technically that’s true, but to me the more intuitive way of describing it would be that it has a dark dorsal stripe, and two dark-bordered white stripes, one on each side.
The origin of the word chipmunk is less clear. One source says it’s from the Algonkian word for “head first”, for the way it descends trees, a second suggests it’s from an Odawa word for “red squirrel”. Another indicates that the “chip” part of chipmunk is in reference to the sound the critters make when alarmed (in the 1830s they were in fact called “chip squirrels”).
Chipmunks are notorious food-hoarders. They spend virtually their whole day searching out food and tucking it away for winter provisions. It’s possible for an individual, if they stumble across an especially rich food source (such as a birdfeeder) to pack away enough food to last their lifetime, nevermind just the winter, in just a single season. Though we tend to think of them as nut and seed eaters, they also eat berries, conifer cones, mushrooms and insects, and even small frogs or birds’ eggs. There’s usually enough food in a single acre of a good-quality forest to support up to 30 individuals, and the only reason there aren’t 30 chipmunks in every acre of woods is that they’re extremely territorial (Alvin, Simon and Theodore being the exception). This is why when you see two chipmunks together they’re nearly always chasing each other.
Just like with the Blue Jays, to aid in their efforts of hoarding food they have pouches on the inside of their cheeks into which they tuck the seed and other foodstuffs they collect. They use their tongue to manoeuver the seeds into the pouches, which together can hold as many as 70 sunflower seeds at once! When full, the pouches bulge in a pretty good imitation of the mumps, nearly doubling the width of the rodent’s face. When they get back to the burrow and want to empty out the pouches they use their paws to push the back of the outside of their cheeks, dislodging the seeds.
They’re pseudo-hibernators, spending the winter holed up and sleeping for most of it. They do enter a torpid state, where their body temperature might drop as low as 5-7 oC (41-45 oF) for periods, but they don’t go into the same deep state of torpor that bears and other true hibernators do, and therefore don’t need to pack on the pounds of fat. When they wake up in the middle of winter they’re able to easily feed from the food they collected over the fall and stored in their burrow. They dig a football-sized burrow about three feet (1 m) underground, and line it with leaves. The lead-in tunnel while they’re working on the burrow can be as much as 10 to 15 m (32 to 50 ft) long, putting the entrance hole quite some distance from the main burrow, which guards against predators so that they can’t just dig around the entrance hole if they find it. Once the burrow is done, they dig a new entry tunnel, and push all the dirt from the new hole back up the old one to plug it so that the mound of dirt on the surface is no longer an indication of an entrance. If they feel like getting fancy, they may add a storage chamber, a “dump” and a restroom to their burrow system.
Most western chipmunks have just one litter per year, but the Eastern has two, one in early spring just after thaw, and the other in mid-summer. When the male chipmunks wake up from their long winter’s sleep in the spring, they’re feeling pretty horny and the first thing they do, after perhaps grabbing a bite to eat so their growling stomach doesn’t embarrass them, is call upon the burrow of a nearby female. If the female hasn’t done her hair and makeup yet she may turn him away until she’s ready. Then all that territoriality that’s maintained over the rest of the year is forgotten, and the couple spend hours cuddling and playing (and mating) together. If two males come to court the same female at the same time, they’ll spend the day chasing each other until one wears out. The victor, the one who lasted the longest, is the one who gets the girl. The same thing plays out in the summer (minus the waking up from hibernation).
Each litter may contain up to 4-5 young. An individual chipmunk, if it survives the learning curve of its first year, may live 2-3 years on average in the wild (a captive chipmunk can reach 8 years) and could produce up to 30 youngsters. The majority of these will be taken by predators, or starve over the winter, and not make it to the following mating season, so populations don’t get overrun by the prolific breeding production. Young are driven off in late spring and early fall, at age 6 to 8 weeks, to fend for themselves. They will either find an old abandoned burrow or dig their own new one to spend the winter.
I don’t mind sharing some of our seed with one or two of these little guys to help them make it through the winter – they’re such characters, the forest would be duller without them!