Short-eared owls

A walk on the dike trail near the Mendenhall wetlands in early March revealed the usual resident Canada geese, grazing in small groups but alert to passing humans some distance away. Gangs of mallards nervously shifted from the edges of an incoming tide to deeper water as humans passed by on the trail. Little flocks of juncos dashed for cover in the nearby trees. It was too early in the season for migrating shorebirds, but I was hoping for something out of the ordinary—and I got lucky.

I don’t often walk out there, because I dislike the tremendous noise of the planes, large and small. But I know that short-eared owls come through on migration or sometimes visit in winter. So it happened that less than half a mile from the trailhead I saw one of these owls swoop up from the meadow, turn in front of some conifers, and sail off over the meadow again.

Then I watched this owl coursing back and forth, low over the grass, many times. The flight style is distinctive: a slow, deep flapping beat with short glides in between, often described as moth-like. This individual landed once, looked down at its feet, and took off again, apparently without prey. It sailed off between the spruces toward the airport, which it may see as just another meadow but the airport officials prefer that it does its hunting elsewhere.

Short-eared owls have a huge geographic range across North America and Eurasia, though South America and into northern Africa. The species has established endemic, resident populations on far-flung islands, including Iceland, Hawai’i, the Galapagos, and the Antilles in the Caribbean. These island populations are different enough that they are ranked as sub-species, but further study may decide they are separate species.

Jan-27-Short-eared-owl-2-5X7
Photo by Kerry Howard

Their name comes from the tiny feather tufts (‘ears’)on the forehead. The tufts are often indistinguishable, showing only when erected; they may be used in social signals with other owls. The tufts have nothing whatever to do with functioning ears that register sounds. The real ears of most owls typically are asymmetrical: the shape and location of the ear opening is different on right and left sides of the head. Along with the facial disc of feathers, that’s what lets them localize their prey so well, even in darkness. The facial disc and ear asymmetry are best developed in owls that only hunt at night. The short-eared owl, however, hunts by both day and night, and uses vision as well as hearing.

Short-eared owls are hunters of open areas, flying low over meadows, sometimes hovering, sometimes scanning an area from a convenient stump or snag. They catch and eat all sorts of prey, from large insects to muskrats and grouse. Birds are major prey in some areas, especially near shorelines where waterbirds are popular food items. But in most places, small mammals, especially voles or lemmings, are the main prey. Both the numbers and the reproductive success of the owls often reflect the abundance of these prey items.

In general, prey is decapitated (or de-winged) before being swallowed whole. Later, the owls regurgitate pellets of neatly packed undigestible bones and feathers. We curious naturalists love to find these deposits, so we can figure out the identity of the victims.

Short-eared owls nest in open areas—grasslands, tundra, marshes. Southeast Alaska is not well-endowed with those habitats, compared to much of the rest of Alaska, and if short-eared owls nest here, it must be uncommon. A pair of short-ears defends an area around the nest from other owls but reportedly does not defend a big feeding territory. As a result, nests are sometimes not very far apart (a few tens of meters).

The female of a pair scrapes out a shallow bowl on the ground, lines it with grass and a few feathers, and lays her eggs. A typical clutch of eggs has about four to seven eggs, but occasionally more, particularly when prey is very abundant. She does all the incubating (about a month); the male delivers food to her. When the eggs hatch, he still brings food to her and she doles it out to the chicks.

She lays one egg a day and starts incubating with the first egg, so the eggs hatch asynchronously, in the order of laying. Thus, the chicks are all of different sizes, and cannibalism of the runts may sometimes happen. The chicks are fluffy and nest-bound for a couple of weeks, after which they start to wander (eldest first, youngest last). But it takes another four or five weeks before they can fly and a year until they mature.

Populations of short-eared owls are declining, due primarily to habitat loss.

Snowy blankets

life in the subnivean world

Snow makes a great blanket (albeit damp and cool), insulating whatever lies below it from cold air above. As we found out not long ago, a few inches of snow kept solid (walkable) ice from forming on ponds, even after many days of single-digit temperatures.

Lots of critters make use of the snow. Ravens roll and toboggan; otters slide. Red squirrels often make winter nests in and under their snow-covered middens. Marten, the most arboreal of the weasel family, find winter resting places under the snow. They often use places where fallen branches and stumps intercept snowfall, creating spaces for resting as well as easier access to subnivean prey. They are reported to rest frequently in red squirrel middens, including those occupied by squirrels. Even birds find shelter under snowy blankets. Ptarmigan make burrows for night-time shelter, leaving little piles of fecal pellets in depressions, which we find in spring as the snow melts from the top of the burrow. Redpolls cluster together in tunnels under the snow to keep warm.

A lot goes on underneath the snows. Invertebrates of many kinds live in subnivean places. There are springtails, beetles and other insects, and spiders, some of them dormant, some of them active at least periodically. They are prey for shrews (which have to eat every few hours) and mice.

Keen’s mouse (the coastal form of the deer mouse) makes snow-blanketed nests in crevices or shallow burrows or cavities in logs and stumps. They often have short periods of torpor, to conserve energy, and make small caches of seeds. Unlike voles, they commonly come above the snow when foraging.

Voles and shrews scuttle along their tunnels, sometimes pursued by voracious weasels (ermine in much of Alaska and least weasel in the interior) that fit easily into those tunnels. Their nests are typically balls of vegetation with a cozy cavity, occasionally appropriated by a weasel that consumed the nest-maker. Meadow voles may even breed in winter if the snow blanket is thick and the food supply is good, but their mortality can be extremely high if the snow cover thins or their nests get wet. Many kinds of voles make winter food caches of roots and seeds and shrews often store prey for later eating.

Lemmings stay active all winter. Brown lemmings harvest the bases of grasses and sedges, as well as a lot of moss (an unusual food, not very digestible). Winter nests under the snow are thick-walled and often lined with their molted fur. The northern collared lemming makes long snow tunnels on the tundra in winter; snow burrows have nest chambers and separate latrines. The winter diet includes lots of low-growing willow bark and buds, reachable under the snow. They may even breed in winter, if the snow cover is really deep. The widespread northern bog lemming is the only lemming in Southeast, living in sphagnum bogs and other habitats. It makes nests and burrows under the snow, but little is known about its ecology.

Pikas are small relatives of hares that customarily live on rocky mountain slopes with nearby meadows. There are two species in North America, one in the Rockies and Cascades, and the collared pika in Interior Alaska and Yukon. All summer long they industriously gather grasses and herbs from the meadows to make hay piles in the rocky talus slopes; each pika may collect over twenty kilos of hay, making many trips per hour. Each pika defends a territory from other pikas and thus protects its haystacks. Most of the winter is spent under the snow, in burrows and crevices, living off the stored hay. Pikas are well adapted to cold but are very sensitive to heat; on hot summer days they hide in the rocks. Warming climate is a serious threat to their populations. In the southern Yukon, average temperatures have risen about two degrees C per decade since the 1960s, and the warming trend has already reduced pika numbers in some areas by ninety percent. There is no place for them to go: they can’t just move higher on the mountains since they are already there, and they can’t cross the warm valleys between the mountains.

Loss of snow cover is just one of the many well-documented deleterious effects of human-generated climate warming.

Hares

wild neighbors, rarely seen

Mid-February, and Parks and Rec hikers are headed up from Crow Hill Road to Lawson Meadows. The skiers soon disappeared, leaving the snowshoe-ers to plod our way up. The lead hikers got lucky—a snowshoe hare dashed across the trail right in front of them. We almost never see the critters themselves, just lots of tracks and occasional pellets. They are nocturnal, and often active in the twilight hours of dawn and dusk. I was not one of the lucky ones, sadly. I think the only hare I’ve actually seen was a young one (called a leveret) that was clamped in the jaws of a cat.

Hares are distinguished from rabbits in several ways, one of which is the condition of the young at birth. Female hares make a simple nest, just a shallow depression. The leverets are born with their eyes soon open, ready to hop about in a couple of days, while little bunnies are born furless, blind, and helpless, restricted for several weeks to a nest, often in a burrow. In general, hares are larger than rabbits, with bigger ears and feet. Just to confuse the issue, jackrabbits are really hares!

Two species of hare live in Alaska. The Alaskan hare is found primarily in tundra habitats in western Alaska, with scattered occurrences along the north coast. It is much larger than the snowshoe hare (well over six pounds vs three or four pounds), which is the smallest hare in the world.

Snowshoe hares are widespread across northern North America and in the mountain chains that extend southward. They live in forested and shrubby habitats where they eat a variety of woody and herbaceous plants. Winter diets include lots of twigs and bark, but sometimes the hares dig down through deep snow to reach buried herbaceous plants. They may even feed, very occasionally, on carcasses. As is common among hares and their relatives (and some rodents also), two kinds of fecal pellets are produced. A soft form is re-ingested (this is called coprophagy), allowing further extraction of nutrients. Then the more fully digested result emerges as a hard, round pellet. In hard times, hares may even re-ingest hard pellets for a third trip through the digestive tract. Pellets are usually deposited singly, so a pile of pellets means that the animal spent some time in that place.

Snowshoe-Hare-in-December-by-Bob-Armstrong
Snowshoe hare. Photo by Bob Armstrong

Northern populations of snowshoe hares are famous for extreme variations in abundance, with around ten years between population peaks, usually. Reasons for these cycles have been much debated. Hares have many predators and mortality, especially of leverets, is high. The Canada lynx preys heavily on hares, and its abundance closely tracks the abundance of hares, peaking with the same cyclic pattern.

Snowshoe hares are solitary creatures, except of course in mating season. They are territorial, defending their home ranges vs. others of the same gender. A reputable Canadian source says that the trampled runways that we see are made deliberately by territory owners. Each runway is trimmed of intruding twigs and herbs and packed firm by hopping up and down, leaving clear escape routes through the territory.

Female hares can produce several litters a year. They can mate right after producing a litter and gestate the next litter while nursing the first. Considering the high energetic cost of lactation, this is noteworthy. A single litter often has more than one father. Birthing a typical litter of four takes just a couple of minutes, after which the female leaves the nest, coming back once a day to nurse her kids. After about three days, the young ones scatter, coming back to the nest in evening to nurse. They can eat solid food when they are a week or so old and are weaned after about four weeks.

The hare spotted by P&R hikers had patches of brown fur mixed with the winter white. Mid-February seems early for the transition to summer coloration. Timing of the molt is regulated chiefly by day length, not by the amount of snow on the ground, so sometimes out-of- synch brown hares are conspicuous on snow and white ones are very visible on leaf litter.

Sensory systems

detecting magnetic fields

We learn that there are five senses (sight, hearing, touch, smell, taste). And we say that there is the “sixth sense”, meaning intuition or a hunch. But there is a physiological seventh sense that detects magnetic fields and, in some species, an eighth sense that detects electrical fields, and perhaps other senses still to be discovered.

Many animals (and plants!) have magnetoreception: birds, turtles, mice, bats, ants, lobsters, bees, newts, fishes, to list a few examples. The capability is also present in bacteria and may be a basic sense in virtually all organisms. However, it is one thing to demonstrate experimentally that an organism is able to sense and respond to magnetic fields, but it is quite another thing to learn how, or if, the magnetic sense is used by the organism.

A real-life function of magnetic sense is known in many animals. For instance, homing pigeons use magnetic sense to locate their home roost. Migratory birds use magnetoreception as well as celestial cues to find the way between nesting and wintering grounds. Sea turtles use this sense to find their nesting beaches and their hatchlings use it, along with light, to find their way to the sea. Some salamanders and toads use magnetic sense to orient themselves to the shore of a pond or to locate their home pond. Certain ants and bees use magnetic (and other clues) to navigate between their nests and food sources. Salmon use magnetic clues, with odor clues, to navigate back to their ‘home’ streams to spawn. An electrical sense of sharks interacts with magnetic sense, allowing them to orient themselves in the ocean.

The plot thickens, however, as researchers discovered magnetic reception and responses at all stages of fish development. For instance, magnetic fields affect the movement of sperm and their success in fertilizing eggs, as well as the size of the resulting embryos and their orientation. The behavior, orientation, heart rates, and hormonal activities of larvae and fry are affected by magnetic fields too. The biological significance of these responses apparently remains to be determined.

And what about magnetic sense in plants, which don’t move around? Experiments have shown effects of magnetic fields on such features as flowering time, seed germination and seedling growth, photosynthesis, the behavior of pollen and roots, and enzyme activity. But the importance of these responses in the real world is anything but clear.

How does magnetoreception work? Only the briefest, most simplistic explanation can fit in the space of this essay. The earth’s main magnetic field has three features that can provide information to suitable receptors. The field varies in intensity, which varies with location and the horizontal or vertical orientation of the force. Another feature is called ‘inclination’, referring to the distance from the surface to the depths of the earth; inclination is very steep near the poles and flatter near the equator, so it gives an index of distance from the poles (i.e., latitude). The field also can provide a compass direction; the declination of a compass indicates deviation from the North Pole/South Pole axis of rotation of the earth (related, roughly, to longitude, and depending on latitude). In addition to the main field, there are local anomalies, commonly caused by magnetized rock.

How do animals sense those magnetic features? Some animals have tiny particles of magnetic material in their beaks, snouts, brains, or elsewhere. Another way involves a protein called cryptochrome, found in both animals (including humans) and plants, which undergoes a complex reaction allowing detection of magnetic inclination. In bird eyes, cryptochrome is activated by blue light and may create a filter for light falling on the retina, making a pattern that changes when a bird moves its head, changing the angle between head and magnetic field. There are other possibilities too. In any case, any information gleaned from magnetic features has to be related to an internal map or some other point of reference, if it is to be used for orientation and navigation.

Note that the magnetic sense is so sensitive that it can work over very small distances, such as when a bird moves its head. It has also been invoked as a possible explanation for how foxes orient that marvelous jump as they pounce with their front feet on a rodent under the snow.

Who eats ferns?

there aren’t many who do!

Ferns are not a very popular food item for the animal kingdom. Compared to the herbivorous insects on flowering plants and conifers, relatively few insects eat ferns. One estimate is there is about one insect species for every twenty species of fern, compared to one insect per one species of flowering plant. The disparity varies regionally, however; Hawaii, for example, has more ferns and more fern-eating insects than some other places.

The insect community on ferns is different from that on other plants. Although many beetles and moths are herbivorous, these taxa are under represented among the fern-eaters. Instead, sawflies and two taxa of true bugs (such as aphids) that typically suck plant juices (rather than chewing the tissues) are more common.

The reasons for the relative paucity of insects that eat ferns are not fully understood. One factor is surely the lack of flowers and seeds, which many kinds of insects use. Another factor probably is the defensive chemistry of ferns. Although they lack many of the defensive compounds found in flowering plants, they have considerable chemical resistance to attack by herbivores.

Bracken fern is notorious for its toxins, although toxin levels vary among bracken populations. This species has been studied intensively, because domestic livestock sometimes eat bracken. If cows and horses eat a lot of bracken, over a period of time the cumulative effects of the toxins can be lethal. Bracken turns out to be loaded with compounds that cause various blood disorders, depress levels of vitamin B1 (potentially leading to blindness), and cause cancer. The most toxic parts of the plant are the rhizomes (underground stems), followed by the fiddleheads and young leaves. A survey of toxins in other ferns would help our understanding of who eats ferns (lady fern, a common local species, is known to be toxic, to dogs, humans, and presumably others, at least if large amounts are eaten; in small quantities, the filicic acid in it help control tapeworms).

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Hoary marmot taking a risk on bracken fern

Vertebrates seem to avoid eating ferns, in general. Among the mammals, white-tailed deer sometimes eat them, and feral pigs in Hawaii eat the starchy tree-fern trunks. Beavers dig up and eat the very toxic rhizomes (how do they deal with the toxins?).

The champion fern-eater is the so-called mountain beaver, a burrowing rodent living in the Pacific Northwest. It is not a true beaver; probably related to squirrels, it is the last survivor of a group that once contained many species, now extinct. More than seventy-five percent of its diet consists of ferns, mostly bracken and sword fern. Female mountain beavers shift away from ferns to a higher protein diet of grasses and forbs when they are lactating, however. Mountain beavers must have a very special way of dealing with all the toxins!

A few vertebrates nibble the spores from the spore-containing packets (called sori) commonly produced on the underside of fern fronds. The European wood mouse does this in winter. The endemic short-tailed bat of New Zealand often forages close to the ground and collects spores. There’s a little parrot in Indonesia that eats fern spores. And the Azores bullfinch eats both spores and leaves in winter and spring. Interestingly, perhaps, I have found no indication that the closely-related Eurasian bullfinch does this.

Humans eat ferns too, sometimes as a springtime change of diet, sometimes more regularly. But there are potential risks to eating very much fern tissue. Clearly, learning more about toxins in a variety of ferns would be useful. And we might learn something from how mountain beavers deal with the toxins. But in the meantime, even though careful preparation might diminish toxicity, it is best to be very cautious about eating ferns.

Strange winter

a bricolage of encounters and observations

December was so warm that beavers stayed active, collecting branches for their winter caches and dam repairs, leaving trails in a thin snow cover. The snow recorded the passage of an otter, sliding over a sand bar in Eagle River. That thin layer of snow also collected a tremendous number of male spruce cones, raising the question of why the trees retained those cones so long after the pollen was shed.

January was more wintery, with a good snowfall and nice cold temperatures. Ptarmigan had come down to the Treadwell Ditch, wandering widely and seldom stopping, apparently not finding much to eat.

On the lower ski loop at Eaglecrest, wildlife had been very active. Porcupines, large and small, had wandered far and wide, leaving their broad furrows and baby-size footprints. As we perched on a log for lunch, a flock of chickadees and golden-crowned kinglets conversed and foraged in a nearby hemlock.

There were lots of deer tracks, of different sizes. The deer trails often followed the edge of the woods, and the lower branches there held only fragments of the dangling lichen Alectoria, suggesting that the deer had been eating one of their good winter foods. Bunchberry plants had been grazed from the bases of trees, leaving stem stubs where deer noses had cleared the snow.

Shrews had left their tiny furrows on top of the snow, leading from one dime-sized hole to another, where a shrew had come to the surface and gone back down under the white blanket. Why do they come out in the open, sometimes travelling many yards before diving back down? That’s a long way to go for the occasional spider crawling slowly on the surface…

Driving out the road, we noticed many small groups of varied thrushes picking small items from the roadside. What are they getting? Grit? Blown seeds? Salt? A subsequent stroll on the Boy Scout beach discovered numerous tiny pinkish shrimp washed up (why?) by a moderately high tide. Ravens attracted by our lunch group lined up on a log came in to scrounge our offerings and then nibbled some of the shrimp.

The long, deep cold in January kept the snow beautifully, brightening the landscape. At my house the temperatures didn’t rise above freezing for many days, dropping to single digits at night. Mrs Nuthatch came to the peanut butter feeder long before there was decent daylight. Mink had been active in several places. One explored the shores of Norton Lake in the Mendenhall Glacier Rec Area, not stopping and clearly going Someplace. Another mink, at Eagle Beach, had made tunnels in deep snow, periodically popping up to the surface but diving right back down. ?Searching?

The prolonged deep freeze let me hope that the ice on the ponds in the MGRA would be sound enough to walk on (with snowshoes, to distribute the weight). However, the ice on Glacier Lake was chancey: there were a few spots of open water and some mushy places. So we crept around the edges to see what we could see. An otter had better travelling over the ice, leaving its trail of prints and a slide between spots where it had dug down through the slushy snow. Was it thinking about getting through the ice to look for fish?

Then warmer weather came back, with rains that ruined the lovely snow. At my house, a raven has come to expect occasional tidbits on my deck railing. One morning I put out some pieces of pie crust. In it came, as if it had been waiting, and grabbed the larger chunks. Then, with the bill crammed, it tried to collect the smaller bits. No luck. So it figured out that it had to drop the big ones, eat the small ones, and then pick up the big ones to carry away.

Down on the surface of my pond, I noticed a female mallard, grubbing for spilled seed in the slush under the suspended feeder. She dug and dug, sometimes burying her whole head, for more than ten minutes. Then she walked to open water downstream, leaving her wide trail in the slush. Late in the afternoon, she came back and did it all over again. I bet this duck is one that hung out here in the summer and remembered this food source.

Aquatic plants

connecting aquatic and terrestrial worlds

Prompted by a discussion with another naturalist, I’ve been thinking about plants that grow in fresh or brackish waters and their unsung importance to animals. So this essay is about aquatic plants (collectively called macrophytes) such as pond lilies (Nuphar), milfoil (Myriophyllum), burreed (Sparganium) , buckbean (Menyanthes), pondweed (Potomogeton), water crowfoot (Ranunculus), ditch grass (Ruppia), arrowhead (Sagittaria), and some sedges (Carex) that play many ecological roles relative to animals. Therefore they also have numerous ramifying effects on many aspects of local ecosystems. Here are some examples.

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Northern Milfoil. Photo by Bob Armstrong

These aquatic plants are eaten by animals. For example, Canada geese nibble the shoots of Lyngbye sedge out on the wetlands; later in the season they grub up the root, leaving characteristic divots. Sedge stands closer to the forest edge are grazed by bears, deer, and sometimes moose. Moose forage on buckbean and other aquatics (see this video by Bob Armstrong), which are reportedly very digestible forage plants and a good source of minerals. Geese, swans, and ducks graze on the leaves of milfoil, ditchgrass, burreed, ditch grass and other species too. Geese and ducks eat the seeds of sedge, milfoil, burreed, ditchgrass , and other species, in some cases passing undigested seeds through the digestive tract and thus dispersing the seeds. All of those animals are, at some point in their lives, potential prey for various predators.

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Swans feeding on milfoil. Photo by Bob Armstrong

Beavers (and humans and muskrats) dig up and eat the nutritious tubers of arrowhead; beavers also eat the yellow pond lilies, buckbean, and soft leaves of several species. Beavers are habitat engineers, creating pond habitat for nesting birds and juvenile salmon. They are prey for carnivores such as wolves; a recent report concludes that wolves are able to plan ahead to set up ambushes for beavers, as well as just running them down on land.

Some of these macrophytes (e.g., water crowfoot, buckbean, arrowhead, pond lilies) produce flowers that are pollinated by insects. The visiting insects may obtain nectar or pollen as food, and they are prey for several kinds of birds.

Damselflies have evolved an unusual use for these plants: female damselflies insert their eggs in the leaves and stems of various aquatic plants, sometimes submerging themselves for several minutes. The emerging larvae are predators on other insects and are themselves (as both larvae and adults) prey for other insects, fish, birds, and frogs.

Macrophytes provide protective cover for small fish, such as sticklebacks and salmon fry, which in turn are prey for larger fish, birds (such as kingfishers and mergansers), otter, and mink. Similarly, toad tadpoles and some aquatic insects hang out in the watery ‘forests’ of pondweed or milfoil, temporarily hiding from predatory insects, fish, or birds.

In addition to providing food, cover, and egg-laying sites, the standing ‘forests’ of aquatic plants provide a handy substrate for dense coatings of algae. Photosynthesis of the algae produces oxygen that improves the breathability of the water. The algae are eaten by toad tadpoles and by herbivorous invertebrates such as snails, which in turn are prey for fish and birds.

These ecological connections are relevant to local ponds (such as Twin Lakes) that are sometimes managed to reduce the density of milfoil and other macrophytes. The species of milfoil in those ponds has been identified as a native species (northern milfoil, Myriophyllum sibiricum). A study of this species (and the invasive Eurasian milfoil, M. spicatum) in eastern North America showed that the native species generally supported more snails and other invertebrates than the invasive species. Those rich communities of invertebrates provide food for fish and waterfowl. Some of the waterfowl also graze directly on milfoil. Thus it becomes important to understand the ecological effects of reducing milfoil density in the lakes. How is the foraging of fish and birds changed? Also, perhaps reducing the density of the native milfoil facilitates invasion by the Eurasian species (widespread in North America and it might be in our area too), which supports poorer invertebrate communities. Furthermore, the invader can hybridize with the native species, changing its palatability or digestibility along with the associated composition of the algal community, with resultant effects on the animals that use milfoil. Hmmm, a potential research project awaiting attention…