By early November, the rain of one of the cold fall storms may have turned to snow, even at the low elevations. In a wind, golden needles float gently down from the Larches. The Aspens and Cottonwoods appear as dead skeletons, though they are very much alive. Their buds, already formed in late summer, are dormant, waiting for increasing photoperiod and warmth in the spring to burst forth. The small, spatula-shaped leaves of Scouler’s Willow, our principal upland willow species, may still be hanging on the bushes, flaming yellow. The wind has scattered most of the fluffy white seed tufts of Fireweed; Smooth Aster still retains some of its parachute-like achenes. Snowberry, in low, shrubby thickets, has dropped most of its opposite leaves, but the fleshy white fruits remain. The prickly stems of Baldhip Rose are gray-brown, but the bean-sized red hips, bare of sepals, provide colorful contrast. If you look closely, you may find signs of gnawing on one of these fruits – possibly the work of a hungry Red Squirrel or American Deer Mouse?
Keep an eye out for a Northern Pygmy-owl perched near the top of a tree, singing a clear, whistled “toot, toot, toot.” Smaller than American Robins, these diminutive owls are fierce predators, sometimes attacking birds larger than themselves. Rarely seen during the nesting season, Northern Pygmy-owls descend to lower altitudes at this time of year, and may stay around the lowlands for the winter.
Cool temperatures slow the movements of Western Thatching Ants, whose dome-shaped nests are conspicuous in somewhat dry, open areas. You may see a conical hole in one of these nests, very possibly the result of a Northern Flicker taking advantage of the slow-moving food. Overhead, you might watch a large, chattering flock of Pine Siskins swoop down into a Western Redcedar, feeding on the seeds, only to take off again in an undulating, shifting cloud. The cones of the Redcedar are starting to open, and a strong wind may scatter the winged seeds several hundred feet from the parent tree. Bohemian Waxwings, crested birds with beautiful, silky plumage in pastel shades of chestnut and gray, may be flocking to concentrations of fruits like Mountain-ash. These birds nest in the boreal forest, migrating south in an unpredictable pattern, looking for abundant fruit. The changes in habitat wrought by human lifestyles have probably altered the winter ecology of this species significantly – certainly, the ubiquitous European Mountain-ash planted in human neighborhoods is heavily fed upon by the Waxwings. Unlike our two native species of Mountain-ash, this one is a tree, rather than a shrub.
By mid November, Bohemian Waxwings, House Finches, Starlings, or others may be finishing up the last few fruits hanging on the smooth, bare, red-tinged branches of Blue Elderberry. If you look up at the crown of a mature Grand Fir, you’ll probably see little brown spikes protruding above the uppermost branches. Grand Fir cones disintegrate on the tree, each leaving a thin, central core. Near the bases of many of these spikes, some seed bracts still remain, like a little cup. Chestnut-backed Chickadees and Pine Grosbeaks are among the birds that can be seen feeding up here, pecking at these yet-to-fall bracts.
If there is snow on the ground, the tracks and behaviors of many forest mammals become readily observable by anyone with patience and persistence. It can be rewarding to do more than simply identify species from tracks. Spending a few minutes or hours following the trail of one particular animal through the snow, asking questions about its speed, gait, and behavior, can give you amazing insights into an animal’s ecology. In paying attention to the trails of White-tailed Deer, I have noticed browsing on some conifer seedlings, especially Lodgepole Pine and Douglas-fir. However, I’ve never seen any browsing on Grand Fir seedlings – perhaps the compounds that make the boughs smell so good are unpalatable to Deer? Following trails through the snow, getting into the mindset of the animal that left them, you will learn surprising things and feel a greater connection with that creature.
By early December, the snow under a Paper Birch may be littered with tiny, winged seeds and whole catkins, although many still remain on the trees. Common Redpolls, small finches with a red cap and yellow beak, feed largely on Birch seeds at this time of year. These birds breed in open boreal forest and in forested pockets of the Arctic tundra; they are known to be quite nomadic in winter. In our area in some years, Redpolls may be quite numerous during the cold months, even staying around beyond the spring equinox. This is correlated with a scarcity of seeds farther north; in other years, few or no Redpolls may winter here.
I tend to think of December in north Idaho as being a cold, snowy time of year, but the instances of periods of warming have been increasing. And so it may be that, after a storm covers the trees with snow and bends the branches with its weight, the snow turns to rain and grows heavier and heavier. Although our conifers have evolved to bend under this weight, the cumulative power of solid water becomes apparent when branches snap under the strain. Or perhaps, nudged by a strong gust, a mature Lodgepole Pine crashes to the ground. This small-scale disaster – the end of this particular tree’s life – also creates life for other species. Within a week or two of the tree’s death, Snowshoe Hare tracks may crisscross the snow. If you were to look closely, you might notice needles clipped by sharp incisors near the ground, or a clean, diagonal cut where a Hare nipped a twig.
True to their name, Snowshoe Hares are well-adapted for northern winters. Not only did they change their coat earlier from brown to a snowy white; they really do have snowshoes, too – in the form of copious fur between the toes of their large back feet. Many predators eat these lagomorphs, including Lynx, Bobcats, Great Horned Owls, and Coyotes. Winter adaptations give an individual Hare a chance to survive the winter in spite of its status as an important food source, and thus allow the species to carry on.
As we approach the winter solstice, the day length continues to decrease. Day by day, the sun’s path across the sky becomes lower, closer to the horizon. As the sun drops behind the western mountains in the afternoon, it illuminates the snowy heights and shows the contours of the landscape. These contours affect microclimates in the mountains. After a fresh snowfall followed by warming temperatures, you may notice that the snow stays on the trees longer in high-elevation creek drainages, melting sooner at a comparable elevation on the intervening ridges. Cold, dense air tends to pool in the mountain valleys; solar heating warms the ridges faster, melting the snow.
December 21 passes, the shortest day of the year in the northern hemisphere. From this point until the summer solstice, the days will grow longer as the sun begins to make a higher and higher arc across the sky. Right now, long before the sun sets, shadows fall across the steep slopes of the ridges that frame east- and west-oriented creek drainages, and chilly air flows down into the draws. In spite of the cold and the long darkness, conifers are not the only plants that remain green. Hidden in the snow you might find Mountain Boxwood, its dark, glossy, elliptical leaves patiently waiting for the spring. Down in the subnivean zone, the interface between earth and snow, Rattlesnake Plantain also retains its white-striped leaves in a basal rosette. In fact, there are numerous plants who use this strategy to survive the winter. These plants can’t talk, but they have much to tell us. If you find bare ground, you might take time to notice and appreciate these beings, who quietly endure conditions unimaginable to us.
On the trunks and branches of trees, perhaps without the benefit of any snow for protection, many species of mosses and lichens remain conspicuous. Lichens are not actually plants; rather, they are symbiotic associations between algae or cyanobacteria (photobionts) and a fungus (the mycobiont). The fungus provides the protecting physical structure of the lichen, while the photobionts live inside and store energy from sunlight. Thus, like mosses (which are plants), lichens can photosynthesize. The next time you are in the forest, you might appreciate taking a few minutes to let yourself notice the diversity of a moss- and lichen-covered tree, rock, or fallen log. With a hand lens, you can really see the intricacies of these lifeforms. Some mosses are creeping, while others are more upright, and there may be many species growing together in a small area. Lichens are incredibly diverse as well, from club-like forms such as Cladonia to the dark brown, hanging hair lichens in the genus Bryoria. Lichens and mosses living on trees are epiphytes, not parasites. Contrary to some people’s perceptions, they do not cause disease in, or take nutrients from, their hosts.
In fact, these epiphytes serve important ecological roles. During wet weather they swell and become vibrant with absorbed water, which they release gradually to their surroundings, reducing rapid runoff. Complex communities of invertebrates live on lichens and mosses, providing food in turn for bark-foraging birds such as Red-breasted Nuthatches. Especially at this time of year, lichens are eaten in significant amounts by Northern Flying Squirrels and Southern Red-backed Voles, important species in the forest food chain. Compared to vascular plants, lichens are generally slow-growing, and some species require long periods without disturbance in order to thrive. For example, Lobaria pulmonaria is a local leafy lichen with a lung-like pattern of ridges and hollows on its surface. Strikingly bright green when wet, it is often associated with moist, old-growth forests. This species contains both an algal and a cyanobacterial partner, and it is capable of fixing nitrogen from the atmosphere.
Because lichens absorb pollutants, they are being used to efficiently monitor air quality. Some species are more sensitive to certain pollutants than others; Lobaria pulmonaria is sensitive to sulphur dioxide. By taking and analyzing samples of indicator lichens, scientists can track airborne contaminants and note changes over time.
Scientific Names of Species Mentioned
Western Larch – Larix occidentalis
Aspen – Populus tremuloides
Black Cottonwood – Populus trichocarpa
Scouler’s Willow – Salix scouleriana
Fireweed – Chamerion angustifolium
Smooth Aster – Symphyotrichum laeve
Snowberry – Symphoricarpos albus
Baldhip Rose – Rosa gymnocarpa
Red Squirrel – Tamiasciurus hudsonicus
American Deer Mouse – Peromyscus maniculatus
Northern Pygmy-owl – Glaucidium gnoma
American Robin – Turdus migratorius
Western Thatching Ant – Formica obscuripes
Northern Flicker – Colaptes auratus
Pine Siskin – Carduelis pinus
Western Redcedar – Thuja plicata
Bohemian Waxwing – Bombycilla garrulus
Mountain-ash – Sorbus spp.
European Mountain-ash – Sorbus aucuparia
House Finch – Carpodacus mexicanus
Starling – Sturnus vulgaris
Blue Elderberry – Sambucus nigra ssp. cerulea
Grand Fir – Abies grandis
Chestnut-backed Chickadee – Poecile rufescens
Pine Grosbeak – Pinicola enucleator
White-tailed Deer – Odocoileus virginianus
Lodgepole Pine – Pinus contorta
Douglas-fir – Pseudotsuga menziesii
Paper Birch – Betula papyrifera
Common Redpoll – Carduelis flammea
Snowshoe Hare – Lepus americanus
Lynx – Lynx canadensis
Bobcat – Lynx rufus
Great Horned Owl – Bubo virginianus
Coyote – Canis latrans
Mountain Boxwood – Paxistima myrsinites
Rattlesnake Plantain – Goodyera oblongifolia
Red-breasted Nuthatch – Sitta canadensis
Northern Flying Squirrel – Glaucomys sabrinus
Southern Red-backed Vole – Clethrionomys gapperi
Retrieved March 24, 2015 from the Integrated Taxonomic Information System on-line database, http://www.itis.gov.
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