If during warmer weather you’ve ever seen what you thought was a miniature kangaroo hopping across a grassy field, you weren’t seeing things. It was a tiny rodent with huge hind feet and a long tail called a jumping mouse.
I’ve only ever seen them while mowing trails through hayfields in the fall.
Though their burnt orange fur is distinctive, it was their kangaroo-like hops across the path ahead of me that really caught my eye.
The individuals I’ve seen were probably meadow jumping mice, but another species, the woodland jumping mouse, is also a possibility.
Without having the mouse in hand, it’s difficult to distinguish between these species, but their natural histories are similar, so I’ll treat them as one.
Jumping mice
Jumping mice are tiny mammals (they weigh a bit more than a chickadee) with huge rear feet and a tail that’s a good bit longer than the body.
Their bellies are white, and the fur on their back (what you glimpse as they bound out of view) is a rich orangish brown. But it is their orange front incisors that give them away: the front surface of each is deeply grooved.
Though this is a definitive characteristic for identification, grooved incisors aren’t likely to be detected unless a cat drops one on the porch.
Though jumping mice can walk and run, when hurried or frightened they hop away in zig-zag fashion. When just moving through open vegetation, each hop measures just a few inches.
But when frightened, they can jump 6 to 10 feet. That startles predators just enough so they often escape to jump another day.
And that’s good because they’re on the menu of owls, hawks, weasels, skunks, bobcats, foxes and snakes.
Hibernators
The most fascinating part of jumping mouse natural history is unfolding right now several feet below ground. Back in the fall they ate madly to fatten up for the winter.
Jumping mice are true hibernators. For four to six weeks they devour seeds, berries, roots, nuts, underground fungi and invertebrates — up to half their body weight each day.
By late October or early November, they’re ready for the big sleep. Though they live and nest above ground during the spring and summer, late fall sends them underground.
They dig a burrow that extends below the frost line and build a grapefruit-sized nest of grass and leaves. When the nest is complete, they plug the tunnel and assume a distinctive sleeping position.
Jumping mice curl into a tight ball by placing the nose between the hind legs and wrapping the tail around the body. Hibernation lasts up to six months.
Body temperature drops to 35 to 40 degrees, and the heart and breathing rates slow drastically. In late April or early May, jumping mice emerge to a bountiful crop of lush spring vegetation.
Though hibernation may seem a safe way to pass a long cold winter, more than half of hibernating jumping mice fail to survive the experience.
The physiological demands of hibernation combine with hunting pressure from small burrow-exploring predators such as least weasels and shrews to make hibernation a risky strategy.
Breeding
Fortunately, the reproductive rate of jumping mice more than compensates for winter mortality and helps maintain a stable population. Breeding dominates spring and summer behavior.
Small balls of vegetation placed beneath logs or inside a large tuft of grass shelter jumping mouse nests.
After a gestation period of just 18 to 21 days, four to six pups are born. Each weighs less than 1 gram. In less than six weeks, young jumping mice are sexually mature, and mice born in the spring’s first litter usually breed their first summer.
Adult jumping mice raise two and sometimes three litters per year. Yes, seeing is believing.
If you think you’ve seen tiny orangish kangaroos hopping across a grassy path, you’ve probably seen a jumping mouse. And that makes you a particularly sharp-eyed curious naturalist.
