This week in the woods, a short-tailed shrew risked a foray out onto the surface of the snow, where its sooty fur stood out against the white. These mammals do not hibernate but rather grow a longer, darker winter coat during the winter and spend most of these months warmed under insulating snow cover. Short-tailed shrews are the most widely distributed shrew in the Northeast, one of the most common North American mammals, and often the most abundant small mammal in a given place.
The fleeting glances we get of shrews in the field impede identification of the six species we have in New Hampshire and Vermont, but these mouse-like allies of moles are all small, with elongated, pointed snouts, pinpoint eyes, and ears miniscule enough for their fur to conceal. Short-tailed shrews may have shorter tails than their compatriots (and shorter snouts as well), but they are the largest North American shrew, sometimes reaching six inches long. Their nearly naked feet, which match their fleshy noses, also help distinguish the species.
Even if infrequently seen, shrews remain active day and night and year-round. They have been recorded to have twelve body movements per second, a heart rate of 700 beats per minute (1,200 if frightened – and capture or loud noises can frighten them to death), and the highest metabolic rate of any North American mammal (60 times a human’s rate). No food for more than three hours can result in starvation, and some shrews consume twice their body weight in a day.
Shrews primarily feed on invertebrates – especially earthworms and also snails, centipedes, and beetles – and in the wintertime depends more on food stored in its burrow, including seeds (especially sunflower seeds spilled from bird feeders) and the tiny subterranean fungus Endogone. “Only seven of the world’s 385 shrew species are known to cache prey,” writes Dan Lambert in an Outside Story article, “and the northern short-tailed shrew is the most accomplished hoarder in this group. Up to ninety percent of its captures are stored in collections.”
Occasionally, short-tailed shrews kill animals of comparable size – mice and voles, hatchlings of ground-nesting birds, and smaller shrews. Especially in these cases of facing oversized prey, it comes in handy that they are venomous (the only venomous mammal in North America). With bites to the throat and face using grooved lower incisors, they chew neurotoxic saliva into their victims, at times killing them but often paralyzing them before dragging them back to their caches. Here, the meat stays fresh longer: an incapacitated mealworm, for instance, can survive for up to 15 days in the underground larder. Short-tailed shrews can then eat their prey at their leisure – sometimes when they are still alive.
Burdened with poor sight and poor sense of smell, short-tailed shrews navigate mostly via sound and, like dolphins and bats, use echolocation. They make ultrasonic clicks too high for the human ear, listen for reflected sound waves, and construct an aural picture of their surroundings that allows them to find solid obstacles and burrow holes as far as two feet away; the ability may even allow them to locate predators and prey.
Maples have the familiar twinned winged seeds with fused pods called samaras – often also called helicopters, whirligigs, and keys. When a seed dries, separates from its sibling, and falls, its ribbed edge slices the air and the thin edge follows; the twirling action generates lift and slows the seed’s descent, allowing it to glide farther away and perhaps even catch an updraft. A single tree may produce samara shapes with wide variability (the basis for evolutionary adaptation), and samaras from different maples can be identified to species by wing shape, seed case shape, angle of connection between two fruits, and color.
This time of year, both striped maple and boxelder (a maple) retain their samaras. Boxelder samaras are especially persistent through winter, and many do not fall until spring. They hang in drooping clusters and have a tan color, much more of a V shape than other maples’, and narrow seeds. Mice and squirrels forage upon the voluminous crops throughout the season, and numerous birds – including cardinals and finches, especially the steeply declining evening grosbeak – depend on them.
Striped maple samaras have wings that make a shallow angle with one another and turn brown over the course of ripening. They hang in pendulous strings, for squirrels, chipmunks, and ruffed grouse to pluck them for their seeds.
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