Two species

an encounter with a wary ermine… and some thoughts about tree swallow nests

On a murky day toward the end of February, I went with a friend on the Boy Scout camp trail. Rain and warm temperatures had turned the snow to unpleasant deep slush and puddles in some places. As usual, we were just looking to see what we could see—and it wasn’t much. There were some crows picking through the wrack on the beach, a tiny group of bufflehead moving farther offshore, and a few geese on the far side of the big meadow. Not even any curious seals popping up to inspect us, no sea lions cruising by. A bit disappointing!

We cut through some of the groves on the big berm behind the beach, where the mosses were happily showing off their many shades of green. One spreading tree sheltered several duck decoys. Then, as I was stepping over a few roots, a movement near the toe of my boot made me stop. A small white head with bright black eyes was peering up out of squirrel-size hole in the ground. I signaled to my friend (who walks faster than I do) to come back. Meanwhile the white head disappeared, but briefly, only to re-emerge once more for a quick look-see. The owner of the head did not like two monsters looking at it, so even though we backed well away and waited, it did not reappear. With its wintry white coat, the ermine (a.k.a. short-tailed weasel; called a stoat in the U.K.) would have been very conspicuous on the snowless ground under the trees. We don’t see ermine very often, and this was the highlight of the walk that day.

The same day, in the afternoon, three female mallards arrived on my icy home pond. One of them had scouted the place two days earlier, and now brought along a couple of friends. They were out of luck, though; no open water and no seeds on the ice. The ducks weren’t the only critters that were anticipating spring, however. The previous week, a bear had crossed the ice into my yard, no doubt allured by the aroma of the peanut butter feeders, and left dirty footprints on my downstairs windows. That was not the only bear report for the Valley—ADFG tells me that there have been other early risers (or poor sleepers) this winter.

Some recent reading included a book called White Feathers, by famous naturalist Bernd Heinrich. It’s about tree swallows, those beautiful aerial acrobats that also sing sweetly—some birds seem to have it all! They are cavity nesters, using natural tree holes and readily using nest boxes.

Among many other observations, Heinrich noted that the tree swallows using his nest boxes had a strong interest in white or light-colored feathers, sometimes collecting them from some distance away. Male swallows were especially interested, although females sometimes showed interest too. Small feathers might make a cozy nest, but they had a special use for long, whitish feathers, chiefly during the later stages of egg-laying and the incubation period.

Of course, I wanted to know if our local tree swallows collected white and light-colored feathers too. And they do: inspection of nest boxes here and in Gustavus found white and whitish feathers around the clutches of eggs.

Those long, white feathers are arranged around the edge of the cup that holds the eggs, placed with the quills poked into the bottom of the nest around the eggs, so that the plumes stand up and arch over the eggs. The feathers clearly are not a cuddly cushion for the eggs, and not a snuggly blanket around them; smaller feathers might do that. They might conceal the eggs, but feathers of any color could do that. So why white ones? Are tree swallows the only species that adorns its nests in this particular way?

Photo by Jessica Millsap. This image was taken as part of the Audubon Tree Swallow Project, under permits from the Alaska Department of Fish and Game and the US Fish and Wildlife Service.

Tree swallows are fiercely territorial, aggressively defending an area and sky-space near the nest, sometimes engaging in knock-down-drag-out fights that end in injuries. They defend a chosen nest cavity against other tree swallows and other cavity-nesting species, including wrens, woodpeckers, bluebirds, starlings, chickadees, and others. The supply of suitable cavities is generally limited and competition for them can be ferocious. In some cases, tree swallows even oust chickadees that have already laid eggs and appropriate the cavity.

The long, whitish feathers, arranged to arch over the eggs, would show up well in dark cavities, easily visible from the nest opening. Heinrich suggests that they might possibly be a visible signal that tree swallows occupy that cavity. When the adult swallows are out foraging, such a signal could be useful in turning away other cavity-seekers and thus avoiding injurious battles. More observation and research needed!

A Wintery Walk

a wonderful weasel encounter

Days are rapidly getting shorter, and the peanut butter junkies at my feeders are voracious. The familiar Oregon juncos that thronged the feeders all summer are now scarce. But I’ve begun to see slate-colored juncos, here from the Interior for the winter. Closely related to the Oregon types (both are usually classed as subspecies of dark-eyed junco), but the new arrivals took at least a week to figure out how to exploit the peanut butter feeder. Maybe they watched the chickadees and got the idea.

On a lovely, sunny but cool and windy, day in mid-October, a little group of friends strolled up the road at Eaglecrest to go off onto the upper ski loop. Darting in and out of the angular rocks that line the road toward the Black Bear lift was a small white critter that disappeared almost as soon as it showed its head. So it took us a little time to ascertain who it was: of course, a short-tailed weasel or ermine (called a stoat in Europe). It then gave us many chances to see it as it explored both sides of the road, around the turn and past the Kimball memorial bench, popping up its head every so often to look around (and perhaps to check on us). The weasel was presumably hunting for something edible, such as a vole or shrew, but we saw no evidence of success.

Photo by David Bergeson

The white winter fur was certainly conspicuous against a background of gray rocks and brown fern fronds. When there’s snow on the ground, of course it’s a different matter—the white fur is great camouflage then, only the black tail tip and a beady black eye marking the beast on a white background. “Our’ weasel apparently had turned its coat from summer brown to winter white well before snow would cover the ground (although a little dusting fell a few days later). Molt is said to be initiated by changes in photoperiod (day length), and modified by temperature, but southern ermine don’t change to white at all. In northern populations, the physiology of molting to winter color is not closely timed to reliable seasonal snow cover; in fact, on snow-free Haida Gwai’i, ermine still acquire a white winter coat. This leaves open a question about why molt is not better synchronized with background color everywhere.

Weasels are built long and slender, which enables them to slip into narrow tunnels, even into vole hideouts in pursuit of prey. However, that elongated body has a lot of surface area (where heat is lost) relative to body volume (where heat is generated), so weasels have a high metabolic rate that generates heat– but necessitates lots of food. An active hunting style presumably provides more encounters with prey (than a sit-and-wait style, for instance), but has its own energetic costs. They need to eat several times a day (taking in about thirty percent of their body weight!) and have a well-insulated nest (often stolen from a victim) in which to rest between hunts. If the usual prey of small rodents is scarce, weasels may hunt hares, squirrels, birds, and even eat worms and bugs and carrion if necessary. They cache dead prey for future meals.

Mating season is in spring, but fertilized eggs are not implanted in a female’s uterus until nine or ten months later. Then the embryos develop into babies in about a month, the newborns staying in the nest for a couple of months or so. Litter size is variable, usually four to eight kits, but well-fed females can produce much larger litters (up to eighteen kits!). Juvenile females become sexually mature while still in the natal nest and may (if a mature male was nearby) already carry fertilized eggs when they disperse to establish their own home ranges. Males can’t inseminate their female litter-mates because they don’t mature until about a year old.

Here are a few more interesting tidbits about weasels: They have excellent color vision, unlike most mammals. They climb well, with reversible ankle joints (like squirrels) so they can descend a tree head-first. If threatened by a superior predator, such as a cat, they may pretend to be dead; if not eaten, they quickly revive and run away.

At this time in October, there was a thin sheet of ice on my home pond in the morning and the ponds at Eaglecrest were ice-covered. Nevertheless, we saw caddisfly larvae in their cases, hanging out on the bottom of a few ponds or moving extremely slowly. They probably spend the winter as larvae, feeding on detritus when possible, but otherwise quiescent; pupation and metamorphosis into flying adults would occur the following year.

A few blueberries clung on their bushes, and I was informed that they were exceptionally tasty. The bright green fronds of deer fern and fern-leaf goldthread stood out on a background of brown, dead and dying vegetation. On the surface of some old skunk cabbage leaves, tiny pools of water had coalesced and frozen solid, forming jewel-like, nearly spherical beads that gleamed in the sunlight.

We ate our lunches in warm sunshine, all spread out in the lee of a grassy bank. The first wintery walk of the year turned out to be a good one.

Wildlife CSI

natural history mysteries

In early November, there were a few late coho in Steep Creek, and a friend saw a pair that seemed to be close to spawning. They hid out under a ledge of ice, in a little pool near some overhanging branches. That was at nine in the morning. At noon, I happened to visit this location, just checking for anything of interest. A big patch of scarlet stained the snow on my side of the stream. Of course, I had to look more closely. Then I found what was left of a salmon: the spine, picked clean, and the skin, turned inside out and covering the tail. I saw no live fish.

All around the bloody remnants were raven tracks, and ravens still perched in nearby trees. Occasionally one would come down and pick minute bits from the bloody snow. But did ravens catch the salmon, themselves? That seemed unlikely, even if they had worked as a team (which they do, sometimes).

Could a mink have been the hunter? There were mink tracks in the snow a few yards away, and some indeterminate, bloodless drag marks on the bank. A full-size coho would seem to be a challenge for a mink that weighs perhaps half as much, but a mink can carry off a chicken, so we can’t rule it out. So, possibly an otter, accounting for the drag marks on the bank, but there were no definitive footprints. An otter could certainly snag a coho from under the ice.

An adult eagle sat, proprietarily or hopefully, in a cottonwood just upstream. No eagle tracks were visible under the carpet of raven tracks, but an eagle could surely grab a coho—and open it up for the ravens to scavenge whatever the eagle left.

Our detective skills were inadequate for the case!

A few days later, on the west side of Mendenhall Lake, Parks and Rec hikers found a matching scarlet stain, but no carcass, on the snow, and a big fish was stirring the nearby waters where a small stream entered the lake. This could have been another would-be spawner that had just lost its partner. A little crowd of eagles watched over the blood-smeared snow, perhaps hoping to nab the remaining fish. And the ravens had been here too, making tracks all over the site..

As we passed the small, wooded almost-island on the west side of the lake, we spotted an ermine (a.k.a. short-tailed weasel), dashing over the ice from the island to the shore. It was just a blur of motion, marked by the black tip of the tail. Its white fur blended superbly with the snowy background.

The white winter coat of the ermine was fine camouflage on the snow. But that lovely fur would be a visual stand-out against the brown leaf litter of the shoreline forest. The ermine’s seasonal change of coat color was out of sync with the existing background in the forest, making it more likely that an owl or other raptor might make a grab for its slender body. The color change is probably regulated mainly by hormonal responses to daylength and perhaps temperature. But there may be an out-of sync transition time in fall, if snow does not come with the shorter days and lower temperatures. And there may be another transition time in spring, as days grow longer and warmer, if brown fur comes in before the snow is gone.

Are ermine whose fur does not provide camouflage in the transition seasons able to choose habitats with more protective cover, to reduce the risk of predation? The evidence is equivocal. There may be some slight compensation for having a prematurely white coat in fall: The winter coat is thicker and provides better insulation, retarding heat loss (and simultaneously slightly reducing incoming heat gain from solar radiation). In spring, however, prematurely brown coats would mean loss of insulation and possible energy costs just to keep the body warm. And besides, it would be possible to change color without changing the thickness of the fur. In short, the problems encountered by coat color changes that are out-of-sync with the color of the background have apparently not yet been resolved by research.

Snowy tracks

stories written on the winter landscape

Snowshoes crunched over deep snow. The sky was cerulean blue and the sun gradually crept around the mountain peaks. These were fine days to be out, seeing what we could see. We were especially interested in the tracks left by the wild critters as they went about their daily lives.

–A shrew left a long line of tiny marks by the side of a beaver pond. Short digressions led to tufts of grass or a buried stick, where spiders and bugs, slowed by the cold temperatures, might be found. Shrews only weigh a few grams and have a very high metabolic rate, so they have to eat almost continually. We often see their trails running over the snow and plunging into miniscule holes that lead under the snow blanket where prey might be found.

–Mouse trails are much less common. But one day we found a line of hopping prints that went out of the forest and across the upper intertidal zone to the most recent wrack line. The piles of tumbled rockweed might harbor small crustaceans, wayward seeds, or lost insects—all suitable for a snack. Another line of tracks went straight back into the shelter of the forest.

–Snowshoe hares had been busy in some areas. They too were looking for food, maybe willow or blueberry buds. But occasionally there were heavily trampled spots, very localized, as if there had been a dance or other social encounter. Popular routes became hare highways, packed flat along a small ridge or between two dense spruce stands.

–An otter had cruised for hundreds of yards along a frozen slough, making side excursions to visit (briefly) several beaver lodges. The deep trough left by its passage seldom came out in the open but usually stayed under the fringing conifers. Reaching the shore of a well-frozen lake, the otter abruptly turned around and went back the way it had come. The only open water on its route was a very small runnel below a beaver dam—a place not likely to hold good otter food.

–Across some thin pond ice, a great blue heron had gingerly minced its way from one patch of open water, at the inlet, to another, at the outlet. Taking very short strides on its long thin toes, it seemed to have been treading carefully. Little sticklebacks and juvenile coho, beware.

–In several places, we spotted narrow grooves on the snow surface, where a slim body had propelled itself on small feet. These wandering trails led to grassy tussocks, dove under logs, circled a pile of branches, disappeared under the snow and came out again. A mighty hunter was at work: a short-tailed weasel or ermine, whose coat turns white in winter, except for the tip of the tail. The short-legged, long body of a weasel is well-adapted for diving down vole tunnels and other tight places. However, that body form means that a weasel can’t afford to put on heavy layers of fat; the belly would drag when the weasel tried to run—not good for a hunter that has to keep moving for much of the day in search of prey. In addition to their small size, the body shape of weasels gives them a lot of surface area (where heat is lost) compared to the body volume (muscles and organs that generate heat), so they have a high metabolic rate to keep themselves warm. And that means they have to eat a lot. They eat mice and voles and small birds, and carrion when it’s available.

–Porcupines seem to wander widely, and we’ve found their trails in many places, often still distinguishable under a layer of new snow. One day we found a very fresh trail of footprints and even some quill-drag; we followed it along a little dirt bank until it disappeared over the edge. Looking down, we saw that a small log, sticking out parallel to the bank, had been wiped clean of new snow by the animal’s passage; the trail ended near the end of the log. Of course, we went around to an easier place to climb down the bank and investigated the trail’s end. There we found a deep burrow, with hairs and a few dried-up fecal pellets and a good barn-y smell, that ran into the bank for over two yards: a snug, dry den that had been used repeatedly for some time. Upon close inspection, that little access log had thousands of scratches, evidence of many balancing acts as the porcupine had ventured out and back.

January frost and snow

explorations in Hilda Meadows

A bright, cold day—just right for a little exploration. A friend and I headed for Hilda meadows: up Trickster (not groomed), onto the groomed upper cross-country ski loop, over the snow bridge on the creek, and through some brush. We found a tiny patch of sun just in time for ‘elevenses’. Tiny indeed, and short-lived; the sun soon rolled around behind the ridge that is the Douglas Island backbone, and all was shady again.

Our perambulations revealed a wealth of animal tracks. The snow was a bit crunchy but not too hard for good tracking. Peripatetic porcupines had trekked long distances over meadows and into the woods. Most of their tracks were quite small, suggesting that these little fellows had been born just last spring. We noticed the one of them toed out more than others and so was individually recognizable.

There were a few squirrel and hare tracks, but not as many as some other times, a possible marten track, one ptarmigan had snooped around some blueberry bushes, and several weasel tracks. Short-tailed weasels or ermine had left evidence of their passing—across the open snow and down under logs and brush and back out again. Then, luckily, we chanced to see, out of the corners of our eyes, a moving blur, which briefly vanished under a stump and peeked out as a pair of beady black eyes on a small white face. The beastie itself! It scooted over to a log and peeked out again. Watching carefully, it apparently decided we were not much of a threat and bounded leisurely off. Ermine are more often tracked than seen, in my experience, so this was great fun. We were interested to observe that its fur was, in fact, not white as snow, but rather yellowish, so it stood out against a truly white background. Had the fur been stained by tannins (which turn many of our streams brownish) in wet moss?

We found a few examples of dead wood with frosty ‘fur’, a less spectacular version of what I reported a week or two ago. On that previous walkabout, there were wonderful sheets of silk-like strands nicely waved; any professional hair-dresser could have been proud of the result. I have recently learned that this phenomenon is actually called ‘hair ice’! The hairs are extremely fine: only about a one-hundredth of a millimeter thick, but they can grow to many centimeters in length. The process is roughly like this: As the water at the surface of the decaying wood freezes, more water is pulled from the surrounding wood, and it pushes out threads of ice from pores on the wood surface. The geometry of the openings of the pores in the wood influences the shape and direction of the hairs.

Somehow, a wood-decay fungus is directly involved, as was suspected a hundred years ago by Wegener (of continental-drift fame). Experimental elimination of the fungus by application of fungicide or heat totally prevents the formation of hair ice. Recent studies in Europe revealed that one particular winter-active fungus (Exidiopsis effusa) is consistently involved in the development of hair ice on a variety of broad-leaved trees. Filaments (technically, hyphae) of the fungus grow along the fluid-transporting vessels and rays of the wood. The fungus digests lignin, which makes wood hard, and also takes up tannins from the decaying wood. So far, so good. But exactly what the fungus does in the formation of hair ice is still a mystery. The decomposed lignin and tannins may provide a ‘crystallization nucleus’ that starts the formation of ice at the wood surface, or they might prevent the tiny ice crystals of the hair ice from recrystallizing into large crystals. And somehow the fungus might help determine the shape of the hair ice. Much remains to be learned!

I have not yet learned if that particular fungus occurs in Alaska, but we do have related species. And we certainly have hair ice. So another chapter of the story is waiting to be written.

New Year’s Day 2012

mustelids and lichens in the muskeg lands

Snow was falling, snow on snow, but—unlike the song—this midwinter day was not bleak at all. With two friends, one two-footed and one four-footed, I set out to explore the forest and small muskegs near the Auke Bay school. This was not our original destination, but we got part way out the road, watched a truck slither and spin out over both lanes in the unplowed slush, and decided we’d find a place closer to town. I’d never been in the area behind the school before, so everything was new to me.

No birds seemed to be active there, but we soon found the trail of a short-tailed weasel, also known as ermine, particularly in winter when the fur is white. It had popped out of a hole roughly the size of a fifty-cent piece, looped over the snow for a few feet, and then dived into the snow again. Both of these snow-holes led to open spaces under shrubs bent under the weight of snow, where mice or voles or shrews might provide a snack. The long, narrow bodies of the weasels allow them to follow their prey into small tunnels.

On the surface of the snow, we could easily see their footprints, with the rear feet landing where the front feet had been, as it took off in the next leap. Each leap covered about a foot of distance. They have such short legs that the fastest way to get around is bending the long, sinuous body to extend the stride.

Short-tailed weasels are ferocious predators, dining on mice and other small mammals by preference, but sometimes eating birds, insects, worms, and even young snowshoe hares. Males weigh up to about seven ounces, but females are considerably smaller. They have high metabolic rates and have to eat a lot every day; females with litters may kill four mice a day.

A bit farther on, we found the trail of a bigger relative of the weasel. This path led hither and yon through shrub thickets, briefly into a tiny rivulet, along a log, under some low-hanging hemlock branches, and into still more thickets. Although we occasionally lost the trail for a little way, we eventually followed it for several hundred yards. We decided the trail-maker was probably a pine marten, partly because the footprints seemed a bit too big and furry for a mink, and partly because no sensible, hungry mink should be so far from the delicacies along the shore.

Trudging through the brush can be easier in winter than in summer. Snow presses down many of the blueberry and menziesia branches, and the two humans on snowshoes could stomp over the bent branches. Our canine companion was less fortunate; her snowshoe-less feet sometimes plunged through the brush piles, to the full length of all four legs, leaving her to wallow her way out.

Even though our broad feet helped us through and over the bushes, we still emerged with our knit caps full of lichens and twigs. And every so often a snow-laden arch of branches would give way, depositing us unceremoniously into a hole. We think this is fun, apparently, because we keep doing it.

Along the way, we noticed an area with a spectacular display of beard lichen festooned on almost every branch. Some of the strands were easily over six feet long. We wondered how it is that there are localized ‘hot spots’ for this lichen. Environmental conditions for good growth, including light and lack of aerial pollutants, must be part of the explanation. But it seems likely that dispersal patterns also contribute to the patchiness of strong lichen colonies: Spores and fragments of lichens are carried on the wind, so the direction, speed, and timing of winds would probably deposit them in semi-predictable patterns. Here’s a complex research problem awaiting a clever young scientist.