Stoneflies in winter

surprising, cold-seeking insects

When the little streams start to open up in late winter and early spring, the snow on either side may be dotted with small, dark objects crawling slowly along. Look more closely, and see that they are slim, winged insects that range in length from a few millimeters to about a centimeter. Sometimes there are hundreds of them, generally moving away from the stream into the surrounding vegetation. They may crawl fifty or a hundred feet or even more away from the water. After mating, females go back to the stream to lay their eggs.

Winter stonefly adult. Photo by David Bergeson

These are the so-called ‘winter stoneflies,’ of which there are reported to be about six species (in four different taxonomic families) in Southeast. The larvae are active in cold water; in fact, they apparently cannot handle warm conditions. After spending their larval lives in the water, they transform into adults; the emergence may be triggered by increasing daylength. They emerge below the surface ice where lowered water levels have created a little space and then find small openings in the ice so they can move onto land. Adults are more cold-tolerant than the larvae and they are exposed to more temperature extremes. Most adults don’t live very long, perhaps a few days or a few weeks, and their main goal is reproduction. The adults of at least some of these species eat algae that grows on tree bark.

No one seems to know why these species emerge so early in the year, when temperatures regularly drop below freezing. They are rather conspicuous on the snow and would be ready prey for hungry birds—but there aren’t as many of those around in February and March as there will be in May, June, and July, when ordinary stoneflies emerge and mate. So some researchers suggest that predator avoidance might make early emergence advantageous—leaving open the question of why more species don’t emerge so early. Other researchers suggest that some as-yet-undetermined negative conditions in the water might drive these species to metamorphose and emerge. Here is a ready-and-waiting research opportunity!

While the ‘winter stoneflies’ are emerging and mating, the numerous other species of stonefly are still in the creek, as larvae. There has been a fair amount of research on the ways in which stonefly larvae (and many other invertebrates) cope with the cold of winter. It turns out that most Alaskan stoneflies are not especially tolerant of cold.

The salient exception is a stonefly called Nemoura arctica, the only Alaskan stonefly known to tolerate being frozen. This species develops slowly in Alaska, requiring at least two years of larval life before metamorphosing into adults. Specimens were collected from the headwaters of the Chandalar River, where temperatures in the streambed in midwinter reached –12.7 degrees Celsius (about nine degrees Fahrenheit). Larvae collected in winter were encased in ice, but most of them survived and became active again when thawed. ‘Anchor ice’ on the streambed is exposed to less extreme temperatures than surface ice, because it is buffered by flowing water.

For comparison, fewer stoneflies tolerate being frozen than midges (Chironomidae), danceflies (Empididae), and some dragonflies (in several families).

Freezing commonly kills organisms because ice inside cells expands and tears cell membranes, ruining the integrity of essential physiological processes. How, then, do dance flies, midges, dragonflies, and one stonefly manage to survive the ice?

Freeze-tolerant insects generally produce ice-binding proteins outside of the cells. Ice then forms around the cells in the extra-cellular spaces, taking up much of the water, so the remaining extracellular fluid becomes very concentrated. Water molecules then move from inside the cells to the outside by osmosis, and the cells effectively become partially dehydrated. In some cases, as much as ninety percent of body water may be lost. These insects run a risk of death from desiccation, if temperatures drop too low and too much water leaves their cells. Furthermore, being encased in ice necessitates being tolerant of low oxygen levels.

Freeze-tolerant insects also produce various types of antifreeze, often small sugar molecules or certain proteins that lower the freezing point of body fluids, protecting enzymes and lipid (fat)-containing parts of the cells (such as the cell membrane).

Still other insects, including some stoneflies, are not freeze-tolerant but would be very susceptible to freezing, except that they make use of the strange phenomenon called supercooling. Extremely small volumes of water (such as those in a small insect) can often be cooled many degrees below the normal freezing point of body fluids (i.e. about – 3 or – 4 degrees Celsius) before freezing occurs. So, for example, a supercooled insect might survive a body temperature of minus fifteen or twenty degrees Celsius. These insects also produce antifreezes that limit the growth of ice crystals in the cells. The risk to supercooling is that virtually any contact can disrupt or circumvent the antifreeze function and allow formation of lethal ice crystals. For instance, soil particles, micro-organisms, or even food in the gut can serve as nuclei for deadly ice crystals. So these insects can’t be very active at all.

Research has shown, however, that the majority of freshwater insects in Alaska try to avoid extreme cold by burrowing down into the substrate below the frost line, or remaining in habitats where water does not freeze. These larvae, including the larvae of ‘winter stoneflies’, stay active through the winter, feeding, molting, and growing.


Plant evolution and life cycles

spores and seeds

Occasionally, friends have asked me about the life cycles of plants, so here I will attempt to summarize them, in the context of plant evolution. I set the stage by describing the basic pattern of life cycles in animals, with which we are more familiar, in order to make the contrast with plants.

Most animal life cycles are relatively simple, compared to most plants. During sexual reproduction, eggs from a female-functioning animal are fertilized by sperm from a male-functioning individual, creating a zygote. Egg and sperm each have one complement of chromosomes—one set of DNA, so when they join, the zygote has two sets of chromosomes with DNA from both parents. Having one set of chromosomes is called ‘haploid’ and having two sets is called ‘diploid—or 1N and 2N for short.

The 2N animal zygote develops into an adult, in some cases passing through an intermediate juvenile stage or several such stages, which may look different and behave differently from the adult form. For instance, caterpillars are juvenile moths and butterflies. But the development is more or less continuous, from fertilized egg to adult, and generally only the 2N adult form is capable of reproduction. The 2N adult produces eggs or sperm that are 1N by the process of meiosis.

In the plant world, things are quite different. Plant life cycles (in plants consisting of more than one cell) in general consist of two phases or two generations. A haploid or 1N phase is typically known as a gametophyte—a plant that produces 1N gametes (eggs or sperm or both). When a 1N sperm fertilizes a 1N egg, the resulting 2N zygote grows into a 2N sporophyte—a plant that by meiosis produces 1N spores that grow into 1N gametophytes. Thus, the life cycle alternates between a 1N gametophyte plant and a 2N sporophyte plant (this is known as alternation of generations).

However, the relative sizes of the gametophyte and sporophyte vary tremendously in the plant kingdom. All plants were derived originally—many, many tens of millions of years ago—from algae (probably green algae), so I’ll start there. Among the thousands of species of multicellular algae, there are many in which the gametophyte is tiny, microscopically small. A zygote—the future and much larger sporophyte—typically develops on the gametophyte, which may then disintegrate. In some algae, however, the gametophytes are large and persistent, easily visible, and about the same size as the sporophytes.

Somewhere along the line, over four hundred million years ago, aquatic green algae found a way to colonize land (possibly by means of symbiosis with fungi). These ancestral algae led to two quite different evolutionary lineages: the mosses, which are small and absorb water and nutrients from air and soil but do not transport them very far internally, and all the other plants (ferns and seed plants), which have internal vascular systems for transporting water and nutrients throughout the plant (and so they are known as the vascular plants).

Moss sporophytes. Photo by Katherine Hocker

In the mosses and their relatives, the eggs and zygotes began to be protected in jackets of sterile cells. The visible mosses that we see throughout our forests and muskegs here are gametophytes (1N). Sperm swim in water to reach eggs on female gametophytes. A fertilized egg (in its protective jacket) on a female gametophyte produces a sporophyte (2N), which we see as a little stalked capsule growing atop a frond of visible moss. The 2N sporophyte reduces the chromosome set to 1N by meiosis, producing 1N spores, which are dispersed and grow into gametophytes. Both of the alternating generations of moss plants are readily visible.

The other evolutionary lineage led to a huge diversity of vascular plants: ferns and their relatives and all the seed plants (conifers, wildflowers, our familiar trees, etc.). Having a vascular system for transporting water and nutrients allowed the plants to grow taller, sometimes much taller, than mosses. Ferns continue the pattern of alternating generations, with a small, typically microscopic, 1N gametophyte and a much larger, 2N sporophyte, which is what we see. Some ancient forms of club-mosses, which are distantly related to ferns, had sporophytes as large as our present-day trees; and even today, there are tree-sized ferns in some parts of the world. Spores from the sporophyte disperse and germinate into the tiny gametophytes in the soil; as in the mosses, water is necessary for sperm to swim to the eggs.

Next to evolve were the seed plants, in which it is the 2N sporophyte that we see. Freely dispersing spores (which would have made independent gametophytes) are not produced. Instead, the 1N gametophytes are now reduced to tiny things on the sporophyte: pollen grains enclosing the male gametophytes and sperm, and miniscule female gametophytes containing eggs (or ovules), inside an ovary. The ovules are enclosed in protective layers of tissue and, after fertilization, will become the seeds. Ecologically, then, the life cycle of seed plants resembles that of animals, with each individual developing from seed to reproductive adult, and the evolutionary history is hidden from sight.

What the seed plants accomplished was finding a way for sperm to reach eggs through the air, rather than depending on water for sperm to swim or float to the eggs. Pollen grains containing sperm are transported by air currents or animals to receptive surfaces that capture the pollen. Sperm then move down a tube produced by the pollen grain to an egg (ovule), resulting in a 2N zygote. The ovules are contained in several layers of tissue, some of which are derived from the tiny female gametophyte and some of which are derived from the large sporophyte. We call these ‘seeds’, and they are often wrapped up in additional fleshy or protective tissue (from the sporophyte) that we call fruits or pods or cones. The seeds of most plants also contain a supply of nutrients to support the growth of a seedling.

Thus, over the millennia, the life cycles of multicellular plants on land have taken several directions. The mosses have gametophytes and sporophytes that are fairly similar in size. The ferns and their allies have tiny gametophytes alternating with much larger sporophytes. The seed plants have reduced the gametophytes to tiny things dependent on large sporophytes, and the alternation of generations is no longer apparent. The evolutionary reasons for all these variations are a subject of scholarly debate.

It is easy to think of the seed plants as being dominant on our landscapes. Indeed, they are the largest land plants today. But the mosses and ferns are still with us, doing things in their own ways; in Southeast, they are important and visible components of the land-plant communities. So they cannot be viewed as merely primitive or evolutionary failures in any way—they are just smaller.

(I have neglected the fungi here. Historically, taxonomists have sometimes classified them as plants and sometimes not. Their life cycles are varied, complex, and quite different from those described here.)

Midwinter rambles

and some thoughts on ravens and wolves

Late January brought us some wonderful snow, deep and fluffy. Of course, after a few days, the temperature rose and the rain came, turning the low-elevation snows to heavy, hard-to-shovel stuff and sending down great lumps of snow from the trees. Very disappointing!

However, before the rains, there was time to squeeze in a couple of little excursions. Parks and Rec went up to Gastineau Meadows on a lovely day, all of us on skis or snowshoes. Shore pines in the muskegs were turned into ‘trolls’ by the great loads of snow they bore (but these trolls didn’t have any bridges under which to lurk). Most wildlife tracks had been smothered by new snowfall, although a few hare and porcupine trails were just barely discernible.

It was a thoroughly enjoyable excursions, nonetheless. We greatly appreciated a group of three young and very courteous snowmobilers who cheerily made room for us pedestrians to pass and even cut their engines so we didn’t gag on the fumes. Well done, guys!

Soon after that, I went snowshoeing in the Mendenhall Glacier Recreation Area, on a mapping expedition with a friend who has a giraffe-length stride. Much of the time we were off-trail, bushwhacking through thickets and tangles. I wallowed along in the “giraffe’s” wake, lifting piles of loose snow with every step. So I began to understand the perspective of a porcupine, nose down, pushing snow aside as it trundles along on its short legs. My understanding improved when I tumbled nose-deep into a partly obscured tree well. Fortunately, the “giraffe” very kindly hauled me out and even presented me with a refreshing cup of tea. And so we went on our way.

Another friend was skiing on Mendenhall Lake one cold day, accompanied by a dog. A raven approached and hopped slowly just ahead of the dog, as if tempting the dog to chase it. The dog did so, briefly, before being called back. The raven tried again but then, getting no response, flitted back and tweaked the dog’s tail. The raven tried one more gambit, in an attempt to get the dog to play. It found a stick, landed a little way in front of the dog, lay down and rolled over, stick in claws, as if offering the stick to the dog. Alas, this dog doesn’t play ‘stick’, so the raven failed to entice it into a game and eventually departed.

Photo by Bob Armstrong

Ravens have been observed to play with wolves, too—tweaking tails and playing tag. In at least one case, the game of tag was played by the raven diving at the wolf’s head and quickly darting up and away when the wolf leaped at it. A daring sort of game, indeed. Bernd Heinrich, who studied ravens intensively, suggests that games of daring are a way to show off to other ravens and build status in raven society.

Were other ravens watching this Mendenhall raven from a distance? Perhaps. Or maybe the bird was really just playing. Anyone who has watched ravens rolling and tobogganing down a snow slope and running back up to do it again, or doing aerial acrobatics, cannot seriously doubt that they know how to play.

Ravens and wolves have a long-standing relationship that may be more complex than previously supposed (of which more, anon, I hope).

Lawson meadows

wet-snow tracks and tiny treasures

The meadows near Lawson Creek are a favorite destination for a Parks and Rec hike or just for exploring. You can now get there from the snowmobilers’ parking lot on Blueberry Hill, up to the Treadwell Ditch, then south on the Ditch Trail and over the new bridge at Lawson Creek. The upstream loop of the old Ditch Trail is now cut off by the new bridge, but you can go partway up the valley on the old Ditch Trail after crossing the bridge or hop right up into a chain of meadows that stretches up the valley.

Or you can start on Crow Hill, go up the CBJ trail to the Ditch and then, instead of going left on the Ditch Trail to Gastineau Meadows, go right. Rather than using the Ditch Trail here, I prefer to go up the little slope into the first big meadow. From there, you just continue around the slope and head up Lawson Valley through the chain of meadows.

Eventually, you run out of meadows and the forest takes over. Parks and Rec usually turns around at that point, has lunch, and heads back down. On a recent excursion, our lunchtime ‘café’ was sheltered from the rain by some tall, dense conifers, and we looked out our ‘window’ at the last meadow.

The snow was heavy and wet, and the skiers in the group found it fast going, making it back to the cars in record time. The snowshoers took a good bit longer. On this wet day, the muskegs on the CBJ trail were overflowing the trail in some places, creating deep slush but no problems for our passage. (Right now, as I write, it is hard to even think about rain and wet, what with low temperatures and howling winds that lift the snow into swirling clouds hundreds of feet tall. The mountain peaks are invisible.)

There were deer tracks in the lower meadows. The deer were sinking in pretty deeply and probably found it hard to move from one relatively snow-free, forested area to another. In winter, deer find their food under the trees, where the snow pack is less than in the open. There were also several sets of snowshoe hare tracks, partially covered by a little recent snow. Best of all was a set of porcupine tracks, small and close together, showing where a young one, now independent of its mother, had wandered around snacking on shrubs.

Two other wintry walks yielded a couple of tiny treasures that I’ll share:

Before the rains, during an earlier the deep-freeze, I found lots of silken threads dangling from branches. The silks were probably left by juvenile spiders, which use these threads to become airborne on a passing breeze. That’s how they disperse away from their mothers to begin their independent lives. On that day, each silk was covered with layers of tiny crystals of hoarfrost, which sparkled like holiday tinsel—only better!

The second little treasure, at the edge of the Mendenhall wetlands, was short-lived. I heard an unusual bird song nearby and soon spotted a magpie under some alders. The bird was fossicking about, occasionally pecking at the ground, and singing a very soft, sweet, delightful little song, all to itself. It sang for several minutes, and gradually went out of sight and hearing in the alder thicket. The bird seemed happy; I certainly was!

Little sounds in nature

the rewards of listening in silence

If we venture off into the forest, away from town and roads (and aircraft, if possible), we often comment on the Quiet. But Quiet in the woods is not silence—it is the absence of human noise. Then we can hear the little sounds and contemplate the small stories they tell.

Most of us notice–at least sometimes–the conspicuous songs and calls of birds. Many folks rejoice at the first song of a varied thrush that in heard in spring. A friend enjoys the ‘rattling key chain’ vocalization of golden-crowned kinglets. Some of us are cheered every time we hear the song of the American dipper. Those sounds are noticeable by anyone who pays a bit of attention. Birdwatchers pay a lot of attention and do almost as much ‘watching’ by ear as by sight.

Not so very long ago, many of us enjoyed a talk by Hank Lentfer and Richard Nelson, featuring their recordings of some natural sounds. Some of these sounds were easy to identify, while others, being much magnified, were harder. Easy or hard, it was an enjoyable and educational presentation.

Taking a cue from those well-known naturalists, I thought it would be fun to think about some of the small sounds in nature, sounds that become perceptible in the Quiet, sounds that otherwise might easily be overlooked. With the contributions of two observant and thoughtful friends, here is a sampling of small sounds that we have enjoyed as we stroll along, stopping every so often to look and listen.

–wing beats of ravens, wind rasping through their feathers as the birds power their way along, in contrast to the slower, softer wingbeats of a heron

–the puff of air as surfacing sea lions exhale, quite different from the puff of porpoises as they pass by

–thud of falling spruce cones, nipped off by a red squirrel

–rattle of lupine seeds as they fall, when warm weather makes the ripe seed pods burst open

–rustling leaf litter as Steller’s jays bury nuts or search for previous stashes

–fluttering leaves as a wren flits through the shrubs, and the wren’s quiet little notes used to keep in contact with others

–creaking of tree trunks in the wind

–a woodpecker flaking off bark scales from a spruce

–clattering of dry leaves falling through twigs and branches

–bill-clacking of nestling herons

–murmuring of a beaver family in its lodge

–scraping of the ‘tongue’ of a banana slug feeding on a leaf

–the distant roar of sea lions and the far-away whoosh of a spouting whale

–whistling wings of goldeneye ducks taking off

–rhythmical lapping of water on a sandy beach or the quite different pattern of water lapping against rocks

–strong wind in conifers compared to that in deciduous trees

–geese talking as they travel north to the nesting grounds or south to the wintering grounds

–waves withdrawing over a pebble beach

–hoar frost crackling when it collapses

–the buzz of a bee changing as it enters a flower

–the grinding of deer or moose teeth when foraging or a beaver gnawing bark from a branch

–lake ice popping and groaning on a cold winter day

I’ve focused here on auditory perceptions. But perhaps it is useful to keep in mind that we can use all of our senses when we are out and about, and doing so can enrich the experience.

March meanderings

a beaver story, wolf tracks, twisted pines, and a raven’s prank

Our meanderings in March produced some interesting observations. One day we followed a tiny creek up a hill, through the forest, to a muskeg. At the edge of that muskeg, our canine companion showed great interest in some blueberry stems. We then saw that these stems had been cut by sharp teeth; just a few feet away there was a small, de-barked hemlock stump, and the upper part of the little tree was gone.

Then we found obscure old footprints in the snow that looked like beaver tracks, and down in a tiny gully were several bark-less blueberry stems. An opening in the ice at the bottom of the gully showed where the bark-eater had come and gone, connecting to the main creek. Of course, we then searched on downstream a short distance and soon spotted a small beaver lodge, with a cache of sticks in a pool not far away. This beaver had built several very small dams, creating little pools at the headwaters of the creek.

This is a strange place to find a resident beaver—and perhaps it is just an overwinter bivouac. The creek is extremely small, maybe just a foot wide, and offers little prospect of creating an extensive pond system. The beaver had harvested blueberry, alder, hemlock, and crabapple sticks, in the absence of more usual fare (cottonwood and willow). Soft, green aquatic vegetation would be rare to absent in this little drainage system, so this summer food would also not be available.

We imagined our beaver—probably a young one—swimming in the salt water from its natal stream as it dispersed to find a home of its own. Then it must have sniffed out the fresh water coming down to a beach and explored its way up to the headwaters of this little creek. At least it could overwinter here.

We were not the only ones to discover the beaver signs. A wolf had left it gigantic pawprints rather recently, as it checked out the lodge and cuttings before cruising over the ridge.

There were other things to see, too: Tracks of deer, porcupine, and grouse. Grouse scat that looked as if the bird had started to shift from winter food to soft summer food. An old, rotten log riddled with beetle borings full of frass (beetle feces) that was better preserved than the wood itself. Very fresh bird scat on the trail, berry-stained and full of false lily-of-the-valley seeds.

Photo by Katherine Hocker

A big, dead, double-trunked shore pine claimed our attention. As do the great majority of dead pines we’ve looked at, this elegant specimen showed a strong twist to the right. In fact, I’d say that over ninety-nine percent of the many dead pines we’ve inspected have this right-hand spiral in the wood. So far, we have found no cogent explanation for this observation; all the suggested published ideas fall far short.

On another hike, at the edge of a muskeg, we were entertained by a raven that flew overhead and dropped something—thud—onto the snow next to the trail. It was a wad of moss and tiny twigs. Oh, I said—nesting material. But something didn’t look quite right (and would moss and little twigs make a thud??). So I reached out and turned over the wad. It was nesting material, all right, but not for a raven. It was an old robin’s nest, mud-walled inside the moss-and-twig mix, and frozen solid. Now the question became—what was that raven really doing? Bombing us, as message? Playing games?


weasels and their kin

One of the treats of a snowy winter is wandering around looking for animal tracks. When I counted up the species for which we’ve found tracks, I saw that one taxonomic family was disproportionately represented—the Mustelidae. Five species of mustelids are likely to leave tracks in snow in our region: ermine, mink, marten, river otter, and wolverine. I’ll first present some basics about mustelids in general, and then some specifics about each of these five species.

Mustelids are a widespread family, occurring on every continent except Australia and Antarctica. There are over fifty-five species, ranging in size from the diminutive least weasel, weighing as little as one or two ounces, to the sea otter, reported to reach over a hundred pounds. They tend to have relatively long, thin body shapes, although some, such as badgers, are stockier; legs are generally short. The claws do not retract (unlike most cats), but again there is an exception: the claws of the fisher are partially retractable. Males are generally larger than females of the same species; their home ranges are larger and tend to overlap those of several females.

They are typically carnivores, preying on a variety of small or middle-sized animals, and sometimes scavengers, although some, such as marten, also eat fruit (and serve as seed dispersers). Much of their ecology is related to availability of food: population abundance, litter size and survival, frequency of reproduction, rate of maturation of juveniles, adult survival (starvation is reported to be a common cause of death in wild populations).

Along with males of many other placental mammals, male mustelids possess a baculum or penis bone. The size of this bone in different species has been suggested to relate to the length of the copulatory act: long bacula are correlated with long copulations. Extended copulations are not generally possible when penile erections depend entirely on hydraulics, i.e. blood pressure. This begs the question of when and where long copulations are adaptive or, conversely, when and where short ones are adaptive. As you might imagine, the subject has attracted some discussion but with no definitive answer.

Most mustelids also share a reproductive habit that (to humans) seems odd: After copulation, the fertilized egg divides just a few times and then rests; it does not implant immediately in the uterine wall, so no placenta is formed and the embryo does not develop further for some time. The delay of implantation lasts several months, during which the few-celled embryo just floats around in the uterus. Eventually, however, it does implant, a placenta develops, and active gestation (just a few weeks long) begins. Thus, the time of mating and the time of active pregnancy are well separated, and birthing is therefore postponed to a season well after the mating season. Delayed implantation is typical of numerous other mammals, including bears and seals.

The adaptive value of a seasonal separation of mating and birthing is often discussed. Most explanations address the importance of rearing young at times of year when food and other conditions are optimal.

This leaves unanswered the reason(s) why mating occurs so long before the season for rearing offspring, and I have not discovered good explanations. In some cases, other aspects of the life history may have created limitations on the convenience of getting male and female together; for instance, bears hibernate for the winter and sexual encounters shortly before birthing are not likely, summertime is surely more convenient; or males take advantage of freedom from child care to go roaming and foraging while females tend the young. I’d like to find a serious analysis of the conditions that favor the seasonal separation of mating and birthing.

Here are a few interesting factoids about our resident mustelids:

River otter—They are very aquatic, eating mostly fish, other aquatic animals in open water or tide pools, and sometimes capturing floating birds from underwater. They can dive to about twenty meters, staying under up to four minutes or so. Being heavy-bodied, they must tread water or scull with the tail to stay afloat. Otters are reported to forage cooperatively in some locations (e.g., Prince William Sound). Otters often travel overland between bodies of water, sometimes sliding over the snow. Their home ranges are said to be smaller on the coast than in the interior, presumably because food sources are more abundant. Otters usually mature at age two years.

Wolverine—They often favor remote areas but use a variety of habitats. In winter, this large mustelid mostly forages by scavenging carcasses left by other predators; its powerful jaws can crack the bones of moose. It is sometimes said that wolverines are too big to survive very long on small prey, too small to kill large game animals regularly, and too slow to chase fast prey. So scavenging becomes a good way to feed. In summer, carrion is less available and wolverines eat more small mammals and birds. They commonly den under deep snow in alpine areas, but commonly travel widely (many miles) to find food. If they get lucky, they will cache surplus food in a handy location. They are slower to mature than our other mustelid residents, usually maturing when three to five years old.

marten. Photo by Matt Knutson

Marten—Denizens of old-growth and mature forests, they are highly arboreal. They commonly feed on small mammals, as well as birds, eggs, and carrion, and are said to need the equivalent of at least three voles per day. However, they can also kill hares and marmots. They mature at age one or two years, depending on food supply. There are two species in Southeast; detailed genetic studies have shown that Kuiu and Admiralty islands are home to a distinct and strictly coastal species (which also occurs on Haida Gwaii and Vancouver).

Ermine—They eat almost anything that moves and need to eat almost continually; they are good swimmers and climbers. They make cozy nests, often usurping the nest of a prey mammal (after eating it), even lining the nest with fur of the prey. Well-insulated resting places are necessary for this small, slender predator that needs this help to keep warm in winter. Sometimes they cache their prey near the nest. Juvenile females can become sexually mature while still in the natal nest, at an age of only one or two months. So, when their mother mates after giving birth (which is the custom with these animals), sometimes the same male will fertilize her daughters as well! They have a short life span in the wild, often living less than two years. Ermine are represented by three distinct genetic lineages in our area, and one of them, with a very limited distribution, is considered to be of conservation concern.

Mink—Comfortable on land and in water, they eat fish, crayfish, various other small aquatic critters, and birds—they are said to be especially fond of bird eggs. They make short dives but usually forage in the shallow water or on land. Mink (and wolverines, ermine, and marten) are adept at climbing. They, like squirrels, are able to descend from a tree rapidly and skillfully, because they can rotate their hind ankles so the claws engage with tree bark. They breed as yearlings, and seldom live longer than three years in the wild.

The populations and historical geographic ranges of marten, wolverine, and river otters in North America have been seriously restricted by human activity: habitat loss including deforestation, over-trapping, pollution (especially otters), reduction of their prey populations. In some cases, reintroductions have restored local populations.

Footnote: (There are three other mustelids in Alaska but we don’t generally see evidence of them here. Least weasels live up north and do not occur here. Sea otters live in the sea, yes, and seldom come ashore. Fishers have only rarely been recorded in Southeast and, in any case, are very elusive.)