The Value of Aging Trees

A big red oak on top of Sapsucker Ridge

A big red oak on top of Sapsucker Ridge

On a hot July day, I sit beneath a large red oak, nestled into a deep buttress, one of several that flare out from this 200-year-old tree. The ground beneath the tree is littered with old acorn remnants as are the bases of the other elders in this stand of deciduous trees.

Protected as a picnic spot by the previous owners, the trees were allowed to prosper even as other portions of our property were cut over in the nineteenth and even twentieth centuries. Instead of fencing a young forest, such as that last 120-acre cutover piece we acquired back in the 1990s, we put up our three-acre deer exclosure in March 2001 around these mature trees.

Now, as I gaze around, I see dozens of oak seedlings and saplings filling in the forest floor. Most are red oaks, but some are offspring of the enormous white oak beside the exclosure gate.

Technically, this is not an old-growth forest but one that is becoming old-growth. Still, it and much of the rest of our property consists of an aging forest. Not long ago, old trees were seen as useless and were harvested so that young trees would grow in their place. But in the last few decades scientists have been discovering that old trees in an old forest are incredible absorbers of carbon dioxide. And red oaks, with their dense wood, are particularly good at absorbing impressive amounts of carbon.

One study, in Massachusetts’s Harvard Forest, found that at 50 years of age, their trees, both oak and maple, were absorbing 0.8 tons of carbon per acre every year. After 15 years, the rate of carbon uptake had doubled. Researchers studying old-growth forests in the West discovered that those forests too absorbed more carbon as they aged.

One of those researchers, Bev Law, of Oregon State University, told a journalist that, “Across forest types, globally, we find that the amount of carbon stored is high in older forests, and that live carbon continues to accumulate for centuries.” This carbon is held not only in the trees themselves but in their fallen leaves and branches as well as in the fertile soil of old forests.

Law is director of the AmeriFlux Network, an international collaborative project founded in 1996 to measure the carbon dioxide, water vapor, and energy in all kinds of major ecological community types or biomes in North, Central, and South America. Using a variety of sophisticated tools, scientists are able to track carbon in any ecosystem. Here in our eastern forests, studies have been done in several states including the aforementioned Massachusetts.

Old trees in an old forest have other uses too. They provide large hollow trees for a variety of birds and animals that use them for nesting, food, and shelter. For instance, sycamore trees are the most massive trees in the eastern United States. They can grow over 100 feet tall and 10 feet wide and live up to 500 years. When they are very old, they have a cavity at ground level large enough, in one recent case, to house a maternity colony of 100 Indiana bats, researchers discovered back in 1993.

A giant eastern hemlock tree in Central Pennsylvania

A giant eastern hemlock tree in Central Pennsylvania

Large, hollow trees also appeal to children of a certain age. I was reminded of Jean Craighead George’s book My Side of the Mountain which my husband Bruce read aloud to all of us when our three sons were young. They were all entranced by the 12-year-old hero of the story, Sam Gribley’s large, hollow tree home in the wilds of the Catskill Mountains. In his case it was a hemlock tree. Remembering the many old-growth hemlocks we have (or had, before the hemlock woolly adelgids killed so many of them in our Pennsylvania old-growth forests), I knew that such trees might have been large enough to house one young boy.

Because our old-growth hemlock trees are mostly in Pennsylvania’s state natural areas, the trees attacked by adelgids have been allowed to die and be reclaimed by the earth as our son, Dave discovered during a recent visit to Snyder-Middleswarth Natural Area. Many people find this wasteful, believing that such trees should be harvested. But Dr. Joan Maloof, who has been writing and speaking about the value of old-growth forests, maintains that “old-growth forests are one of the few land uses where topsoil is created instead of destroyed.”

We like to think that our own younger but mature forest is also creating soil as we allow our trees to fall over and rot, creating, as our young nephew Patrick once cried over and over, “Dirt, dirt, dirt” while sifting the powdery, reddish-brown remains of red oak branches through his fingers. Those powdery remains of the heartwood and sapwood appear to be a nursery for the downy rattlesnake plantains I’ve discovered inside and outside our exclosure. When we first put up the exclosure, I found a large colony of this orchid growing on a slope where several trees had rotted down to heartwood and sapwood. Another plant that we found outside the exclosure and fenced had germinated beneath a stump that was seeping rotted wood at its base.

Then, a couple years ago, I found still another downy rattlesnake plantain plant that had germinated on the decaying remains of a fallen red oak limb. At the same time, I noticed that the fenced plant outside the exclosure was looking poorly. I gathered up more of the “natural” fertilizer from the trunk and sprinkled it over the plant, and once again it is thriving. I haven’t seen any studies that indicate that downy rattlesnake plantain needs this material, but I wonder.

Photographing downy rattlesnake plantain in our deer exclosure

Photographing downy rattlesnake plantain in our deer exclosure

As our forest has aged over the last 41 years we’ve lived here and now nearing one hundred years of age in our hollow area, our forest bird diversity has increased. Fallen trees across our first-order, headwater stream, attract several breeding Louisiana waterthrushes and winter wrens. Barred owls court and nest in our larger, hollow trees. Scarlet tanagers, worm-eating warblers, and red-eyed vireos, among others, are more common than ever. Once we had no nesting black-throated green warblers, cerulean warblers, blue-headed vireos, winter wrens, or Acadian flycatchers, but our aging forest has attracted them. All of these bird species and several more, such as blackburnian warblers — depending on whether species need coniferous, deciduous or mixed deciduous forests — use older, mature forests. And the larger these forests are, the better the chances are for the birds to fledge nestlings.

The same is true for many mammal species. Bears, raccoons, and porcupines, for example, like to den in large, hollow trees. One study of black bear den trees found that in order for red and white oak trees to be big enough, they had to be between 175 and 280 years old, which reminds me of the huge oaks our boys found more than 30 years ago at the steep base of our mountain on a property line with a neighbor. They took some box camera photos of themselves standing in front of them and they looked as if they were as large as California redwood trees. I was amazed and delighted, but before I had a chance to see those trees, our neighbor’s logging operation had cut them down. The boys went to check on them and said that they were all hollow inside, so excellent habitat had been destroyed and not a dollar earned on those trees.

The same den tree study found that raccoons liked tree hollows in trees from 90 to 164 years old, and gray squirrels 65 to 130 years in age. Many bat species, too, like old trees with cavities and loose bark. Other opportunities for denning in older forests include in soil pits created by large root masses of wind-tilted trees, in the root masses themselves, and in stumps, logs, large, horizontal limbs and cavities in standing trees, all of which we have in abundance in our aging forest..

One special kind of older forest that has diminished greatly is that of mixed red spruce and hemlock in the northern tier of Pennsylvania. Such a forest especially appeals to red-backed voles, water shrews, and state-endangered northern flying squirrels. According to researcher Dr. Carolyn Mahan of Penn State, this type of coniferous forest creates a moist microclimate that supports a diversity of fungi, which both the voles and the northern flying squirrels thrive on. They also spread the fungi spores, thereby enriching the soil. Water shrews also seem to prefer such forests, but they like them to be in swampy ravines.

Megalodacne heros beetles feed and mate on varnish shelf fungi, found on an ancient hemlock logs

Megalodacne heros beetles feed and mate on varnish shelf fungi, found on ancient hemlock logs

We also have red-backed voles in our deciduous forest, and Mahan explains that they are not specific to old red spruce/hemlock forests, but more of them are found there than in forests such as ours. Northern flying squirrels are much rarer in our state because they are habitat specialists and their red spruce/hemlock forests have been lost to habitat fragmentation from development of all kinds and to hemlock woolly adelgids. The remaining smaller, patchier coniferous groves next to deciduous forests also attract the more generalist and numerous southern flying squirrels. They are sharing nest sites and even hybridizing with northern flying squirrels, and in the process, passing on a roundworm species, Strongyloides robustus, to which they seem to be immune but which is killing the northern flying squirrels.

Mahan has 600 nest boxes in 21 study sites for the northern flying squirrel, and this year not one northern flying squirrel has been found in any of those boxes. Last year she and other researchers planted an experimental 2500 native red spruce seedlings among the dying hemlocks of a site and others in a recent Game Commission clearcut which was fenced to see if they will grow and thrive and someday produce more red spruce forests. If they do well, they will plant more red spruce seedlings. But think how long it will be before there will be another red spruce forest as magnificent of those we had in Pennsylvania. How much better it would have been if we had saved larger pieces of our older spruce forests.

After talking to Mahan and other researchers, I am more determined than ever to keep growing an older forest. But on this hot summer day, I most appreciate our mature forest for its deep shade that cools not only me but all the creatures large and small that live here.

All photos by Dave Bonta ~ click on images to view larger versions at Flickr

April Journal Highlights (2)

Close encounters of the avian kind

April 18. The sun warmed the Far Field, and as I walked Pennyroyal Trail, a towhee sang, a flicker called, and a ruby-crowned kinglet sang. I stopped to “pish,” hoping to entice the kinglet into view, and I did. He flew on to a tree branch, erected his ruby-crown, and sang, giving me my first look at what I had been hearing for weeks.

I went on to the woods beyond the Far Field where a brown-headed cowbird sang and a ruffed grouse crept off into the underbrush. I imagine he was the drummer I stalked back in early April. Sitting still on a moss-covered, old log, I also heard a red-bellied woodpecker, eastern towhee, and northern flicker as the dead leaves rustled in the wind.

The sun quickly disappeared, and I picked my way through the woods until I encountered two excited white-breasted nuthatches on a tree trunk. At first I thought they were courting, but then I realized that they were drinking from sap wells. They were quickly driven off by a male yellow-bellied sapsucker.

As soon as he disappeared higher in the tree, the female nuthatch returned for a few furtive sips. Still, the sapsucker quietly worked on new wells, sipped from old ones, and chased off a ruby-crowned kinglet. Occasionally the male sapsucker flicked his wings as he worked or flew over to an adjacent grapevine as if to rest. Surely there is no tasty sap in a grapevine. The irrestible sap wells are on a pignut hickory, as usual, and it is encircled up its trunk with old sap wells.

The nuthatches returned, calling softly, as they drank from the lower sap wells while the sapsucker worked high in the tree drilling new ones. At last I left the relatively peaceful scene, two species sharing one resource.

April 20. I used my turkey call as I sat in the spruce grove and called in a hen turkey. She came close to my hiding place at the edge of the grove and then retreated back to the edge of the woods along First Field Trail, clucking all the way. I’ve never called in a hen before, but according to one of our turkey hunters, that’s not unusual. Still, experts disagree on why they respond to a hen call. Is she already setting on eggs and defending her territory? Is she a scout for a male turkey or trying to keep rivals from joining “her” gobbler? Is she recruiting more hens for “her” gobbler? Is she merely curious? Are there reasons that we can’t even imagine?

Then, walking back on the Far Field Road, I scared up a gobbler. He, of course, saw me and ran, but I did get a quick look at his long beard. Was he still searching for hens? If only I had tried the hen call along the road. Oh well! It’s obvious that the turkeys are restless and have perhaps not gotten together yet due to the cold.

Above the barn on Butterfly Loop at dusk, the woodcock called, turning around to direct his call in all directions as we watched from a respectable distance.


Gray squirrels and masked shrews: social behavior

April 21. At least three young gray squirrels were born in the black walnut tree nest hole beside the driveway. Today they emerged for the first time, or at least two of the three did. I sat watching on the veranda as first one emerged and stayed out, exploring nearby branches. Then the second emerged more briefly and stayed closer to the nest hole before going back into it again. Each squirrel chewed about the hole entrance, hanging upside down before emerging. When both squirrels were out, a third one peered timidly out of the hole, but stayed inside. All their climbing about, peering in and out of the hole, even their chewing was silent. But scolding from a distant adult squirrel sent them all back into the den hole with one looking out. Three adults harvested black walnuts on the lower lawn.

The first six-spotted tiger beetle gleamed bright green on the driveway.

April 23. The gray squirrel family, even the shy one, played in, out, and around their nest hole as we watched from the veranda.

April 24. I heard a black-throated green warbler in the woods near the powerline right-of-way singing both his songs. As I stood listening and watching, a masked shrew dashed in and out of the leaf duff along an old, barkless, fallen tree. I sat quietly, watching for the shrews, and heard the first blue-gray gnatcatcher of the season. As I continued on the trail, a pair of mallards flew past on the powerline right-of-way, heading toward the First Field. Were they the same mallards Dave saw earlier in the morning? Had they gone back to Sinking Valley? Who knows? But at least I saw them.

More masked shrews chased in the woods on the other side of the powerline right-of-way. They crossed right in front of me for several minutes so I sat down on the trail and watched as they dashed back and forth across the trail, always using the same pathway at my feet. They were tiny, grayish-brown, with peculiarly-shaped snouts that identified them as masked shrews. I counted half a dozen or more chasing about. They were silent to my ears except for the rustling in the leaves. The books say that they are looking for food, but I only see this phenomenon in April and sometimes in July and I think it has to do with mate-chasing. None of the books say anything about their sex life. I suspect they have two broods a year, but I can’t prove it. Finally they stopped and I continued my walk.

The return of the wood thrush

April 27. Sitting on the veranda reading near dusk, we heard the first whip-poor-will of the season singing above the garage at dusk.

April 28. A pair of northern flickers checked out the black walnut tree squirrel den. Were they waiting until the young gray squirrels leave so they could take over the nest hole?

April 29. I stepped outside early to listen for the wood thrush, but the towhees were so loud they blocked out more distant sounds. Still, I did hear a faint portion of a wood thrush song. I stopped and gave thanks that another spring had come and with it wood thrush music–three months of heavenly singing before they once again leave us.

On Dogwood Knoll a rose-breasted grosbeak sang. And then, as I descended the knoll on a path of blooming dwarf cinquefoil, I heard the singing of a Louisiana waterthrush above the dark place. Halleleujah! We have at least one singing male. I sat on Turkey Bench to listen to his ringing tones.

Down near the bottom of the mountain I heard the “tick-tick” scolding tones of another Louisiana waterthrush. I rested on a moss-covered log beside the stream, still hearing but not seeing the waterthrush.

Bruce came down the road and a small, black, white and orange moth spun around his hat and landed briefly on it. Then it landed on my hat and Bruce photographed it. It was a grapevine epimenis, Psychomorpha epimenis — an early, day-flying moth whose caterpillar feeds on grapes. Truly a beautiful little creature.

In mid-afternoon, Steve pointed out a black vulture sailing over First Field.

April 30. At breakfast I watched a northern flicker throwing to the wind the remains of the squirrel nest in the walnut tree. Those flickers had been checking on the den every day, evidently waiting until the squirrel family dispersed.

Walking up Guesthouse Trail, I finally heard the wood thrush singing clearly. Wild black cherry and striped maple trees have leaved out and already my view into the woods has diminished.
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See also my post at the Plummer’s Hollow blog, Spring wildflowers: back on track.

Shrew Business

In the gray, gathering gloom of an imminent February snowstorm, I stopped to watch a northern short-tailed shrew foraging on the edge of our powerline right-of-way. On this day it was a breezy 22 degrees Fahrenheit and patches of bare earth alternated with patches of frozen snow.

The shrew had scuttled past a mere five feet away. Then it paused and used its long, mobile, cartilaginous snout to poke in leaf litter and dried grasses in search of food. Next it pushed its snout under a snowy patch for ten minutes and busily ate whatever it had found.

That was when I slowly eased myself down on my “hot seat” to watch it. The shrew was too close to focus my binoculars and remained oblivious to my presence. It pursued its prey vigorously, its pointed snout questing, its clawed back feet pumping, its front feet digging like a frantic terrier. Once it pulled what looked like a caterpillar from beneath the leaf litter and chomped it down.

A small, plush, charcoal-gray, furry ball, it scuffled over the snow. Its pink nose constantly sniffed while its naked, pink feet scratched the thin snow layer or the open turf. The little creature ate so much that it even paused to excrete.

After almost 45 minutes of high-octane hunting and eating, the shrew ran under a log at the edge of the woods. Probably it was returning to its apple-sized resting nest. Constructed of grasses, sedges, and leaves in the shape of a hollow ball, the nest is located as much as six to 16 inches below ground or beneath logs, stumps or old boards. From the nest, openings lead to a complex underground burrow system that includes separate food-caching locations and latrine areas.

Mostly northern short-tailed shrews (Blarina brevicauda) sleep in the winter to reduce their need for food. But such periods are alternated with intense, active hunting periods that usually occur below the snow cover where it is warmer. Researchers claim that northern short-tailed shrews spend only brief periods above ground during cold weather, but this one, at least, was undeterred by the damp cold.

On a much warmer day in late May I heard a rustle in the dry leaves beside First Field Trail. Again it was a northern short-tailed shrew. This time it ranged over the forest floor, in and out of the leaf litter, along the sides of fallen logs, and atop beds of mosses as it looked for food. Once it tried to grab a centipede but missed. It also lunged twice at a small toad. Finally, it disappeared underground.

I have been enamored with these small, fierce creatures ever since I discovered my first northern short-tailed shrew dashing frenetically around the bottom of an old bucket I had set in our basement sink one winter almost three decades ago. I knew it was not a mouse but just what it was puzzled me. After a little research, I identified it and discovered to my surprise that it was only one of seven species of shrews living in Pennsylvania and 312 species worldwide! Found on every continent but Antarctica and Australia, shrews make up 25% or more of the species richness in northcentral and northeastern North America, especially in wet sites.

Shrews belong to the family Soricidae and first evolved soon after dinosaurs disappeared 38 million years ago. Since then they have remained almost unchanged. Most have five clawed toes on each foot, a long, pointed snout that extends beyond their jaw, a wedge-shaped skull, and sharp, pointed teeth. Those in the eastern United States possess minute eyes and a highly-developed sense of smell and hearing.

Of the seven Pennsylvania species, five belong to the Sorex genus (Sorex being the Latin word for “shrew”) and, except for the larger water shrew (S. palustris), are difficult to distinguish in the field.

Water shrews are primarily denizens of rocky-bottomed, rushing mountain streams in forests of hemlock, spruce, and rhododendron although they also have been found in bogs, dry creek beds, and near small springs. At 5.6 to 6.2 inches in length, they are the longest of Pennsylvania’s shrews. However, they are outweighed by northern short-tailed shrews, the largest shrew species in the state. Water shrews are further distinguished by their long, bicolored tails and bodies that are gray above and white below.

Their large, broad hind feet are equipped with stiff hairs on the sides of their toes that hold globules of air. This allows them to perform the seemingly miraculous feats of walking and running on the surface of water. They are adept swimmers and divers even under ice in the winter as they pursue their small aquatic prey. These are shrews I would love to see in action, but they are rare enough to be listed as a threatened species in Pennsylvania.

One Sorex species I have positively identified on our property is the smoky shrew (S. fumeus). I found one dead in the woods, popped it in our freezer, and later took it to Dr. Joseph T. Merritt, shrew expert and Resident Director of Powdermill Nature Reserve, the biological field station of Pittsburgh’s Carnegie Museum of Natural History. (For more information on Merritt’s work with northern short-tailed shrews, see my February 1997 column.) Merritt was quickly able to distinguish my smoky shrew from other Sorex species because it is larger (4.3 to 5 inches) than all but the long-tailed shrew.

Also called “gray shrews,” they like damp, dark woods with dense ferns and other ground cover shaded by a canopy of second-growth timber–the kind of environment we have here–and they eat small invertebrates of the leaf litter. Smoky shrews live with or near deer and woodland jumping mice, red-backed and pine voles, hairy-tailed moles and northern short-tailed shrews, and they use burrows of other small woodland animals. When disturbed they are liable to throw themselves on their backs and wave their legs while emitting grating, high-pitched calls.

Long-tailed shrews (S.dispar) resemble smoky shrews except for their longer tails, slimmer bodies, and darker coloration. But they prefer to live under and among rocks or boulders, especially talus slopes, hence their other name “rock shrews.” In Pennsylvania their favorite food is centipedes.

Then there are the two smallest, look-alike Sorex species–the masked shrews and pygmy shrews. They can only be told apart by examining their teeth, even though the pygmy shrews (S. hoyi) have the honor of being the smallest mammals in North America. Although they prefer dry mountain habitats, they can also be found in open fields and along the edges of woods. They make their tiny burrows below stumps, fallen logs, and forest leaf carpets and eat twice their weight (that of a dime) in insect larvae, spiders and beetles every day. Unlike most shrew species that produce two to three litters a year, they have only one.

I’m almost certain we have masked shrews (S. cinereus) here and so is Merritt because of the behavior I have observed. Over the years I have often been stopped by rustling and twittering sounds in the leaf litter. Tiny bodies dash in and out of the leaf cover and under and along logs. Sometimes they are so intent on what they are doing that I can sit on a log while they run under my legs. It is difficult to get a good look at them and an accurate count of their numbers, but I’ve seen up to five at a time. Masked shrews are most famous for this behavior, yet so far no researcher has positively figured out why they do it. Some think it is connected with courtship (they do have three litters of four to ten young a year) and others believe it is connected with food gathering. C.R. Vispo observed running masked shrews in a mountain forest in western North Carolina and found that their stomachs were stuffed with fly larvae. Another researcher mentioned that the larvae of some flies may travel in long, snake-like masses over the forest floor. Shrews, with their keen noses, would easily detect such a phenomenon. On the other hand, the running I have observed has occurred only in the spring and summer when masked shrews are courting, mating, and raising young.

Masked shrews are the most widely distributed shrews in North American, living in Alaska, across Canada, and south into the northern half of the United States. They need a shaded, moist habitat and eat tiny mollusks, insects and their larvae, small worms, and the carrion of larger animals.

Finally, there are the endangered-in-Pennsylvania least shrews (Cryptotis parva) that look like smaller versions of northern short-tailed shrews. Also called “bee shrews” because they enter beehives in search of larvae and pupae, their major foods, they like drier habitats than the other shrews. A grassland species, they live in grassy, weedy and brushy fields and forage in the runways of meadow voles. Least shrews breed from March to November and are sometimes found together in nests, as many as 12 and 31 in Texas nests and 31 in Virginia. Although most shrew species are solitary creatures except during courtship and breeding, researchers believe that both least shrew parents care for their offspring.

Shrews in general communicate mostly through scent and vocalizations and the masked, northern short-tailed and water shrews use echolocation especially when they are exposed to strange situations. Researchers think that echolocation may be a way for them to explore a new habitat without attracting predators. Of those they have plenty–owls, house cats, hawks, opossums, raccoons, snakes, foxes, weasels, bobcats, and herons, to name a few. Because they possess high metabolisms, they must eat almost constantly and most small shrews die of old age after a year. Only northern short-tailed shrews live longer–2.5 years.

Much more needs to be learned about these tiny, voracious, pugnacious creatures. Over the last couple decades, shrew research has expanded. As the t-shirt of Pennsylvania wildlife biologist Jim Hart puts it, “There’s no business like shrew business!”

Winter Survival Champions

“It’s amazing. I can’t believe there’s anything here,” exclaimed Dr. Joseph Merritt.

Resident Director of Powdermill Nature Reserve, the biological field station of Pittsburgh’s Carnegie Museum of Natural History and author of Guide to the Mammals of Pennsylvania, Merritt is a specialist in small mammals. To learn more about the lives of such creatures as deer and white-footed mice, woodland jumping mice, southern red-backed voles, southern flying squirrels, eastern chipmunks and short-tailed shrews, Merritt has been live trapping them for over sixteen years. On a cold afternoon in February, with two inches of fresh snow on the ground, my husband Bruce and I were accompanying him on his rounds.

The January flood of 1996 had occurred less that a month before our visit. A portion of Merritt’s trapping site along Powdermill Run had been under water and the traps and their protective chimneys had washed away. Merritt had quickly replaced them and, to his amazement, was finding new animals, specifically short-tailed shrews, in that area. Somehow they had learned that the previous residents were gone (presumably drowned) and were already claiming new territory in the winter. Of the eight short-tailed shrews he trapped that afternoon and the following morning, four were new animals in the flood zone and four were re-captures from higher ground. He also found two flying squirrels and two red-backed voles in traps further up the slope, the latter among large rocks that we clambered over and around.

Merritt sets two metal Sherman box traps, protected from the elements by a wooden chimney, ten meters (about 33 feet) apart in his wooded study site of one hectare (about two and half acres) by one hectare, and has a total of 200 trapping sites in all. Baited with sunflower seeds and padded with synthetic-fiber nesting material, the traps are monitored in early morning and late afternoon three days of one week, every month of the year. The short-tailed shrews are toe-clipped because of their tiny ears, the other mammals are ear-tagged for identification so Merritt can distinguish each captive. He also weighs and sexes them and checks their reproductive status.

In the summer he may find as many as 100 traps occupied; in the winter the number is much smaller. That’s because the woodland jumping mice are hibernating, having reduced their body temperature from a normal 98 degrees to 33. Many of the others, such as chipmunks, flying squirrels, and mice, undergo temporary torpor, reducing their temperature to 60 degrees and then periodically arousing to eat stored food. Southern red-backed voles and short-tailed shrews, however, are active all winter long.

Although Merritt studies small mammals year round, he is particularly interested in their winter survival techniques. Years ago, as a graduate student at the University of Colorado in Boulder, he had monitored the individual development and population changes of wintering southern red-backed voles at 11,000 feet in the spruce-fir forests of the Rocky Mountains. Eight days a month he snowshoed into his site and found each trap by digging through snow beneath markers in the trees. He was still snowshoeing in and brushing snow from his traps in early June when he made an electrifying discovery–a two week old vole born under the snow two months before the snow would be gone. In other words, southern red-backed voles not only survived in the winter successfully under a heavy snow pack but they reproduced.

This discovery solidified Merritt’s interest in winter ecology, a discipline pioneered by Russian scientists in the 1930s and 40s. But instead of staying in Colorado, Merritt, a California native, came to Powdermill.

“Once I saw the Appalachian forests, I was hooked,” Merritt told us. Even after sixteen years, he continues to be delighted by the beauty and diversity of eastern woodlands.

His study site at Powdermill is in a mature second growth forest consisting primarily of American beech, yellow poplar or tulip, sugar maple, cucumber magnolia and red oak trees with an understory of striped maple trees, spicebush, witch hazel, and rhododendron. Selectively logged in the early 1900s, the site now has many large trees and a small mammal population of approximately 250.

At Powdermill Merritt is able to study the winter survival tactics of the same southern red-backed vole (Clethrionomys gapperi) that he studied in Colorado, because it ranges in the west along the Rocky Mountains to New Mexico and Arizona, across Canada and the northern United States, and in the east along the Appalachian Mountains south to northern Georgia. This beautiful little creature is easily identifiable by a broad, reddish band running from its forehead to its rump and its bicolored tail, dark brown above and whitish below. It lives in coniferous, deciduous and mixed forests with an abundance of rotting logs, stumps and exposed roots and eats nuts, seeds, berries, mosses, lichens, ferns, mushrooms, plants and arthropods.

After twelve years of live trapping them at Powdermill Merritt determined that they ranged in density from five to 36 voles a hectare. Their winter survival techniques include: reducing their body size in the autumn and winter so they need less food; shifting their food preferences to readily available seeds, roots, bark, and plant parts; foraging under the snow and in subterranean burrows where they are not affected by snow or bad weather and where it is warmer; and engaging in non-shivering thermogenesis (heat production) or NST.

NST is an important winter survival technique not only for red-backed voles but for short-tailed shrews as well. Between their shoulder blades near their spinal cords, they have high energy, heat-producing tissue called brown adipose or brown fat which functions like a blanket to keep them warm. Merritt found that it was especially effective during mid-January, the coldest days of the year at Powdermill.

Despite all these techniques, however, red-backed voles lose weight throughout the winter. In contrast, short-tailed shrews actually gain weight. Merritt calls them the “champions at winter survival.”

Northern short-tailed shrews (Blarina brevicauda) are the largest of North American shrews and one of our most abundant mammals. They live in a wide variety of environments–forests, fields, thickets and grasslands–wherever there is a thick layer of leaf litter and humus where they can construct their intricate underground burrow system. There they hunt invertebrates such as spiders, centipedes, slugs, snails and earthworms as well as salamanders, mice, voles, mushrooms, and plant material. Often, when sitting under a tree in our woods, I can hear the high-pitched squeaking sounds they make. They also use ultrasonic sounds to echolocate objects in their dark burrows.

Short-tailed shrews are smelly creatures, emitting a musky odor produced by oily skin glands on their sides and bellies, which is why cats will kill but not eat them. They are also one of only a few poisonous mammals in the world. Their toxin, similar to that of a cobra’s, immobilizes but does not kill their prey. It slows down their victim’s heart beat, blood pressure, and respiration, making it comatose so it can be stored for three to five days and provide fresh food whenever it is needed. To make sure no other animal eats their prey, they mark it by urinating and defecating on it and cache it in abandoned mice nests. This food caching ability is one of their winter survival techniques.

Until Merritt conducted radiotelemetry studies on short-tailed shrews, they were thought to use huddling as another winter survival technique. Flying squirrels, mice and voles all form group-huddles in a communal nest which help to keep them warm. Not so the belligerent, highly territorial, and individualistic short-tailed shrews. They live alone year round. But the underground nests they build are so well insulated that they are considerably warmer than the above ground temperature. The soil-leaf litter zone where they forage primarily for insects and insect larvae in the winter can be more than 50 degrees warmer than the outside temperature in mid-January and as much as 59 degrees warmer within their tunnels. They also reduce their activity during the coldest periods, staying active only seven to 16 percent of the day. The rest of the time they sleep.

As we accompanied Merritt on his rounds we were impressed by the dedication that drives him on, even in a light snowfall the following morning, even after a couple tumbles on the rocky mountainside, setting and checking hundreds of traps day after day, year in and year out. He admitted that in the milder months he often has help, but in the winter he is usually on his own. He works quickly and efficiently, handling the creatures as little as possible. No matter what the weather, if the traps are set, he checks them, even during the flood when the bridge spanning Powdermill Run was under water.

“I don’t want them to die,” he explained. Unlike some small mammal biologists, he does not kill any of his study animals. In fact, during an earlier visit to his site, in late October, I was struck by the affection he seemed to have for all the small mammals he showed us. He was especially concerned for the wellbeing of his short-tailed shrews.

“Shrews make life real difficult,” he told us. “They’re so temperamental they die if it thunders.” They also chitter loudly the first time they are captured, even before he toe-clips them, something he does not like to do. But it is the only way to get the kind of information on population dynamics that he needs. And after their first capture, the repeats do not protest at all. Many, in fact, are seemingly happy to eat the sunflower seeds in return for a brief minute or two of handling.

During our winter visit, Merritt added to his data. He learned that short-tailed shrews move into a desirable, deserted territory fast, even in winter. One of the newcomers was a big animal–21.5 grams and two weighed 14.5 grams. Although short-tailed shrews cannot be sexed unless they are nursing, he could sex the red-backed voles. One was a male probably born last summer. Another was an unusually big female–30 grams. And one of the flying squirrels, who had never been caught in that particular box before, was a female with a swollen vulva, an indication that she was beginning her reproduction cycle. Like all the flying squirrels he captures, summer and winter, new captures and repeaters, she screamed like a banshee until he released her. Then she flew to one of the 30 flying squirrel boxes hammered on to the trees in the study site.

“I never get tired of seeing them fly,” Merritt commented. Despite what seems at times, to be repetitive, difficult work, Merritt gets more joy from his work than most people, I suspect. To interact with such a charming cast of characters as the diverse small mammals of an Appalachian forest has its rewards and I felt privileged to have had a close-up view of creatures I have often observed from afar in our own Appalachian forest.