Shrews may resemble mice but they are different

Shrews are one of the smallest mammals in North America and the smallest one resides in North Idaho--the pygmy shrew. The pygmy shrew weighs between two and four grams, roughly the weight of a pencil. Other shrews that reside in North Idaho include the American water shrew, masked shrew, montane shrew and vagrant shrew.

Shrews may look like mice but they are significantly different because they belong to a different order containing insectivores and they have pointed noses, small ears and tiny eyes. Like voles, identifying a shrew on the species level is difficult.

Shrews resemble mice but they have a pointed snout, small ears and tiny eyes

One unique aspect of a shrew, if you can catch one or find one dead, is that they all have reddish tips to their teeth. Shrews can also be identified by five toes on all feet whereas mice have four toes on the front feet and five toes on the hind feet.

All insectivores use senses besides sight to find food, mainly hearing, touch and smell. Shrews have many characteristics that allow them to forage for insects. 

Shrews have tiny eyes because they don’t rely on sight to find their food. Their pointed snout helps them burrow through soil to reach grubs including earthworms, insects, spiders and other small animals such as young mice, salamanders, snails and slugs. Some shrews even use echolocation like bats to find insects. 

Since their sense of smell is extremely important for finding food, a larger portion of their brain is devoted to their sense of smell. Once shrews find an insect, they catch the insect with their two enlarged, pincer-like upper front incisors that protrude forward. 

As big eaters, shrews eat at least their body weight in food each day. If they don’t eat frequently they may die of starvation so shrews store food in their nest. This voracious appetite doesn’t keep shrews from being picky eaters. Shrews prefer fresh food, even fresh stored food.

With a diet of insects, storing fresh food may seem unlikely but shrews keep their catch fresh by crushing the prey’s skull and biting off the legs. This keeps the insect alive until the shrew eats it. Shrews have sharp, pointed teeth adapted just for crunching on insect exoskeletons. 

While shrews may have a voracious appetite and a unique way of storing food, they are not on the top of many predators food list. Many shrews emit a musky odor from scent glands that resembles a skunk odor and effectively deters most predators except for owls. 

Like some mice, voles and lemmings, shrews are mainly nocturnal but will also be sporadically active during the day. They burrow in the leaf litter or humus layer to travel or travel in the burrows or runways made by voles and moles (also an insectivore). 

Like the water vole, the water shrew readily takes to water and lives around streams and ponds. The water shrew can even run on water because of the long, stiff hairs between its toes and along the sides of feet that trap air bubbles. 

Many of the shrews, mice, voles and lemmings survive the cold winter temperatures by living in the subnivian zone. This zone stays within one to two degrees of freezing regardless of the air temperature if there is adequate snow cover. 

Occasionally, tracks of these small mammals can be seen on the surface of the snow scurrying between trees or clumps of grass. However, the small mammals don’t stay on the surface long because they are more prone to predation, even if they possess a musky odor. 

Look for shorter tails on voles and lemmings

Scurrying around underground, in meadows and through leaf litter are several small, furry mammals. Last week, I wrote about the mice found in North Idaho and this week, I’ll focus on the voles and lemmings.

There are five native species of voles in North Idaho and one species of lemming: southern red-backed vole, western heather vole, meadow vole, long-tailed vole, water vole and northern bog lemming. Identifying individual vole species can be very difficult.

Voles and lemmings are grouped together in the same family and both are stocky-bodied and short-tailed with ears more or less concealed in their fur. Bog lemmings look like voles with really short tails. 

Compared to mice whose tails are almost the same length as their body, the tail of a vole is considerably shorter. The southern red-backed vole’s tail extends about 1.5 inches from its four-inch body. Voles and lemmings are also typically darker colored than deer mice.

Voles are active throughout the day because they feed on low-energy food that requires frequent eating. Voles and lemmings are primarily herbivores, foraging on fungi, seeds, nuts, berries, lichen, bark, green vegetation and roots depending on what is available in their habitat.

The habitats that voles occupy in North Idaho include damp forests with fallen logs, mountain meadows, clear-cuts, bogs, alpine areas, grassy areas, brushy areas, and along streams and ponds. 

Meadow voles are the most common vole in North Idaho and the most widespread vole in North America. Signs of meadow voles, like most other voles, are more common than seeing the vole itself.

Predators can find voles, lemmings and mice beneath the snow

Meadow voles create runways through grassy areas and leave piles of cut stems along the runways. The runways are especially visible after the snow melts since voles remain active in the subnivian zone (insulated layer between the ground and snow). Their globular nests of grass constructed in the subnivian zone are also revealed when the snow melts.

Meadow voles make air holes (roughly one-inch in diameter) up to the snow’s surface to allow carbon dioxide to escape from their subnivian tunnels. These air holes don’t have tracks leading up to them on the surface but meadow voles do travel on the snow’s surface and leave tracks. 

One aptly-named vole is the water vole which swims well and burrows into banks above and below the water level. Look for water voles along streams and ponds through alpine and subalpine meadows.

Less common than voles are bog lemmings. The northern bog lemming has almost no tail (it is three-quarters-of-an-inch long) and its body is nearly four inches long.

Northern bog lemmings are found in bogs, wet meadows, alpine tundra or openings in forests. Bog lemmings create runways on the surface like meadow voles and they dig shallow burrows underground. They also live in the subnivian zone in the winter.

Despite the differences between mice, voles and lemmings, they share the same rung on the food chain as an important food source for many predators, including weasels, foxes, owls, raptors, bobcats and coyotes. On the other hand, shrews have very few predators because of a special characteristic which will be revealed in next week’s column covering the last small, furry mammal. 

Small, furry critters include more than mice

Signs of the smallest mammals are more frequently seen than the animal itself unless you happen to see one scurry across the road. Mice, voles, lemmings and shrews are some of the smallest mammals in Idaho. 

While they all seem to be small, furry critters, there are significant differences between mice, voles, lemmings and shrews. One major difference is that shrews are insectivores while mice, voles and lemmings are rodents--two different orders in the classification system.

Mice exhibit a slender build with prominent ears, large eyes and well-developed whiskers. Voles and lemmings are relatively thick-bodied with small ears, snub nose, short tail and beady eyes. Shrews resemble mice but have pointed noses, small ears and tiny eyes.

Mice, voles and lemmings are rodents along with beavers, porcupines, squirrels, chipmunks and rats. All rodents share the characteristic of a prominent pair of incisors in the front of both the upper and lower jaws which supports their mainly herbivorous diet. 

The trails of mice, voles, lemmings and shrews are often seen more in winter than the animals themselves

There are two native species of mice in North Idaho: the American deer mouse and the western jumping mouse. The house mouse is an introduced species also found in Idaho and throughout the United States. 

The American deer mouse is a small- to medium-sized mouse that is nocturnal and active year-round. They range in color from dark-brown to orange-brown on their back with paler sides and a white belly. Their tail is equal to or slightly shorter than their body length (averaging 3.5 inches). 

Deer mice occupy almost every habitat because they eat a variety of food-- seeds, fruit, insects and subterranean fungi-- and store extra in caches. The woodland form of the American deer mouse capitalizes on food found in trees since it can climb well. 

Deer mice nest in hollow logs, underground burrows, birds’ nests, mattresses and among rocks. 

House mice share many characteristics with deer mice but the house mouse’s tail is less hairy and its coat more gray. House mice tend to have a pale or gray belly unlike the white belly of deer mice. 

House mice are also nocturnal and can climb well. They are most well-known for eating human food, soap, grain in agricultural areas and other items in buildings. House mice are less likely to be found in the woods and instead are found in agricultural areas, roadsides and in buildings in rural and urban areas. 

Another small rodent found in North Idaho is the western jumping mouse and is different enough from the other mice to be classified in its own family. Jumping mice have the same contrasting belly as the American deer mouse but its tail has a small tuft of fur at the tip.

Jumping mice have extremely long, narrow tails and exceptionally long, hind feet that allow them to leap six to ten feet in a single bound when alarmed. They are less likely to be seen since they are mainly nocturnal and hibernate. 

The jumping mouse hibernates for eight to ten months of the year. In the fall, jumping mice eat enough grass seeds, fruit, fungi and insects to accumulate a layer of fat for the winter. However, only about one-third of jumping mice survive hibernation. 

The best place to catch a glimpse of western jumping mice is along streams through mountain meadows. 

North Idaho’s three species of mice live in a variety of habitats but shouldn’t be mistaken for voles and lemmings, which I’ll cover in next week’s column.

Being green in winter isn’t easy

Compared to the Midwest, the forests of North Idaho are filled with more conifers than deciduous trees. Conifers keep our forests green through winter as do their evergreen counterparts hugging the ground. 

Evergreen plants, including conifers, can photosynthesize during winter despite the cold temperatures

While not as bright and vibrant as deciduous plants that steal the show in the summer, evergreen plants peaking through the snow keep the forest floor green in winter. One of the most obvious is Oregon-grape with its pointy leaves. A few other evergreen plants growing in the region include kinnikinnick, Labrador tea, bog cranberry, creeping snowberry, white and pink mountain-heather, crowberry and prince’s pine.

Unlike deciduous plants that lose their leaves in the fall, evergreen plants (as the name implies) stay green by keeping their leaves year-round. Every single leaf isn’t kept every year. Some conifers retain their needles for two to three years before shedding them. 

For the most part, evergreen plants keep their leaves to conserve energy. Often evergreen plants grow in areas where nutrients are sparse, so growing an entire set of leaves every year is costly. 

Evergreen plants are more prevalent at higher latitudes and higher elevations because the growing season is shorter. Growing all new leaves every year has to be advantageous for the plant instead of keeping the leaves year-round. 

White mountain-heather is an evergreen plant that grows at high elevations

For deciduous plants, one of the advantages of shedding leaves is the reduced chance of damage from snow and ice. An early snowfall when the leaves are still on deciduous trees exemplifies the damage that can occur when the branches become too heavy with snow and ice. 

Conifers possess a unique shape that allows for snow-shedding and their leaves (needles) are also smaller than deciduous leaves and catch less snow. 

A benefit of keeping leaves year-round is that evergreen plants can continue to photosynthesize during the winter. However, the rate of photosynthesis is significantly slower in the winter than in the summer. 

Photosynthesis is the process of using light energy to convert carbon dioxide and water into sugar and oxygen. Light and carbon dioxide are available in the winter but water is less available. 

Water is a key factor for evergreen plants in winter. Water doesn’t move as quickly from the roots to the leaves in winter and less water is available from the soil. Often evergreen plants rely on water stored in the stems for photosynthesis. Some plants can even obtain snow meltwater through their leaves or thinnest bark. 

With precious water in the leaves, evergreen plants have to be careful not to loose it and they have several adaptations to prevent water loss. Water loss happens because water vapor moves from areas of high concentration (inside leaves) to areas of low concentration (air). 

Most evergreen plants have a waxy coating on their leaves to reduce water loss and also to protect new growth from ultraviolet radiation. Without a waxy coating the leaves would dry out quickly. 

Oregon-grapes have a waxy coating on their leaves to prevent water loss

Evergreen leaves also have tight stomatal closures which are holes in the leaves that allow for air exchange (carbon dioxide in and oxygen out). 

Other ways evergreen plants reduce water loss are by having dense foliage to reduce air movement and by having a fuzzy underside on leaves to create a zone of insulation. Both reduce the concentration gradient immediately outside the leaf and, therefore, help reduce water loss. 

Even if photosynthetic rates are slow in winter, evergreen plants can take advantage of spring warmth and increasing sunlight to jumpstart their growing season. For low-lying evergreen plants, spring and late fall may be the only time deciduous vegetation doesn’t overshadow them and block their sunlight. 

Why is the sky blue?

When a child colors a picture of the sky, the sky is blue and the sun is yellow. Why isn’t the sky green and the sun purple? 

The sky appears more blue in the mountains because there are fewer aerosols to scatter white light

The color of the sky is determined by what is in the atmosphere. Without an atmosphere the sky would be black, like what astronauts see from the moon.

Sunlight consists of a broad spectrum of electromagnetic radiation traveling at different wavelengths. We see the visible light portion of the spectrum (violet, indigo, blue, green, yellow, orange and red). The sunlight travels in a straight line until something reflects it (mirror), bends it (prism) or scatters it (gas molecule). 

The atmosphere is filled with different components, such as gas molecules, water droplets and dust, and each component scatters different wavelengths of light depending on the component’s size. 

Our eyes perceive clouds as white because water droplets in clouds scatter white light

Aerosols (such as soot, water droplets and dust) are larger components in the atmosphere and scatter all wavelengths of light. Gas molecules are smaller and scatter shorter wavelengths and blue light has a short wavelength. When blue light is scattered it goes in all directions and that is the light that strikes our eyes. 

Other colors of light pass through the atmosphere without scattering and aren’t visible until they reflect off an object. Then we see the yellow daffodils, green grass and purple plums. 

If blue light scatters in all directions, why isn’t the sky uniformly blue on a clear day? You may have noticed that closer to the horizon the sky is a lighter blue or even whitish. 

The sky near the horizon often appears a lighter blue 

When the sun is directly overhead, sunlight passes through the least amount of atmosphere. The more atmosphere sunlight passes through, the more chances there are for the light to be scattered and rescattered in all directions. This scattering mixes the scattered colors together again so we see more white and less blue. 

The same reason applies to why clouds are white and hazy days are whitish. On cloudy or hazy days, there are more aerosols in the atmosphere (such as water droplets) and these aerosols scatter all wavelengths of light, causing them scatter, rescatter and mix back together. 

Scattering also influences the color of sunsets. Since the sun is low on the horizon, sunlight has to travel a greater distance to reach our eyes. This extra distance provides more opportunities for blue light to scatter in every direction. So much scattering happens that red and yellow light is all that is left to reach our eyes. 

Sometimes the whole western sky appears red, especially if it is smoky from a forest fire, because large particles (like soot) reflect and scatter more of the red and yellow light. If there are fewer particles in the atmosphere, the sunset will be more yellow or orange. 

Light traveling a longer distance causes sunsets to be red, orange and yellow  

After the sun sets, the sky sometimes turns a purple hue. The purple hue is a result of red light reflecting off aerosols higher in the atmosphere and mixing with scattered blue light to reach our eyes as purple.

However, during and right after sunset, the entire sky doesn’t turn red, orange or yellow--the sky overhead is still blue. The sky is still blue because of the ozone. Ozone absorbs the longer wavelengths of light (red, yellow and orange) and leaves the shorter wavelengths (blue). At sunset the light travels its longest distance in the atmosphere and the ozone filters out most of the wavelengths, leaving the sky blue overhead. 

A mixture of red light and blue light turns the sky purple after sunsets

The color of the sky can change color for a variety of reasons. But we can be certain the sky will be blue on a clear day and the sun yellow, just as kids depict it. 

Note: Published in the Bonners Ferry Herald on Feb. 27, 2014.

First Robin

Despite cool morning temperatures in the teens, the robins are back. This morning I saw a flock of eight robins in the tree tops. They weren't singing their cheery song yet.

Looking back at my calendar, this year's robins are five days earlier than last year when I saw the first one on Feb. 27. In 2011, I saw the first robin on March 9.

Stromatolites a window into Earth’s history

Fossils offer a glimpse of what organisms have lived on Earth, such as woolly mammoths and Tyrannosaurus rex, and most don’t exist today. Some fossils resemble modern-day counterparts, such as ferns and petrified wood, and others have living examples, such as stromatolites. 

The irregular lumps of rock at the base of the Kootenai River swinging bridge upstream of Troy, Montana are fossilized stromatolites.

Stromatolites are structures created by cyanobacteria (also known as blue-green algae). The internal structure resembles a cabbage while the outside can look mushroom-shaped, loaf-shaped or cauliflower-shaped. 

Cyanobacteria create stromatolites by growing in layers in shallow marine water. Cyanobacteria grow in mats with nearly three billion cyanobacteria covering one square meter. As sediment is deposited over the cyanobacteria from tides and wave action, the cyanobacteria grow up through the sediment. Layers of sediment then alternate with layers of cyanobacteria.

If you’ve noticed the rocks around the base of the Kootenai River swinging bridge, they look like cream and black cabbages sliced open--these are fossilized stromatolites. The black layers are carbon-rich layers from when there was little deposition of sediment and the creamy layers are from periods of higher deposition. 

Alternating organic-rich (dark) and sediment-rich (light) layers can be seen in this stromatolite

Stromatolites grow slowly, so slowly that it can take 100 years for five centimeters of growth or 2,000 years for a stromatolite to reach one-meter high.

When living stromatolites were discovered in 1956 by scientists in Shark Bay, Australia, they were the first ever recorded examples of a structure previously only found as a fossil in ancient rock. 

Stromatolites are one of the oldest fossils on Earth. Worldwide, the oldest fossilized stromatolites are found in South Africa and date back 3.2 billion years. The stromatolites around the Kootenai bridge are part of the Belt formation, a Precambrian sedimentary formation dated between 600 million and 800 million years old.  

The roughly concentric circles are fossilized stromatolites

Stromatolites and the cyanobacteria that created them played a crucial role in shaping the atmosphere of Earth. Like all green plants, cyanobacteria absorb carbon dioxide from the atmosphere, use the carbon to build tissue and then release the oxygen. 

During the Precambrian, the atmosphere contained very little oxygen. With the growth of stromatolites and the spread of cyanobacteria around the Earth, the atmosphere became more oxygen-rich and less carbon-rich. 

The harsh conditions of the Precambrian, with its carbon-rich atmosphere, hot temperatures and intense ultraviolet radiation set the stage for cyanobacteria to thrive at that time since little else could.

Living stromatolites are found in three places on Earth today: Shark Bay and two places in the Bahamas. Cyanobacteria thrive in Shark Bay because the water is twice as salty as normal seawater due to the restricted flow of the bay. In the Bahamas, stromatolites are found in sub-tidal channels where the currents are very strong and few animals can survive. 

The internal layers of stromatolites can be a variety of shapes

Burrowing and grazing marine animals are the demise of stromatolites because they destroy the layers. Therefore, as marine animals populated the oceans, the range of stromatolites decreased to places that were too hostile for animals to survive. 

While there may only be a few places on Earth to view living stromatolites, those places offer an opportunity to study a living example of a fossil and determine what affects growth. Scientists have determined tides, temperature and sunlight control the growth of cyanobacteria. So not only do scientists have insight into the conditions on Earth three billion years ago but living stromatolites are keeping a diary of the current conditions on Earth. 

Note: Published in the Bonners Ferry Herald on Feb. 20, 2014.

Caching allows early nesting for Clark’s nutcracker

Laying eggs in March would be a risky venture for most birds because of the lack of food available to feed nestlings. But an alpine resident--the Clark’s nutcracker-- has a system figured out to circumvent that issue.

The Clark's nutcracker is a member of the corvid family which includes gray jays, crows and ravens

Like the gray jay, the Clark’s nutcracker caches food when food is available. With a diet consisting mostly of conifer seeds, a Clark’s nutcracker caches between 35,000 to 98,000 seeds between late summer and fall. These cached seeds are the nutcracker’s main food source until the cones are ripe again the next year. Nutcrackers also opportunistically forage for insects, spiders, small birds, small mammals and carrion.

In the northern Rockies, Clark’s nutcrackers mainly forage for the high-protein seeds of whitebark pine, ponderosa pine and Douglas fir. A diet of different seeds is a survival strategy because both ponderosa pine and whitebark pine are masting species (produce a large cone crop every few years). 

Since nutcrackers cache seeds, they keep a home range. The home range isn’t usually productive enough to harvest 98,000 seeds, so the nutcracker forages up to 20 miles away for seeds. 

Obtaining the seeds isn’t easy, which is why the Clark’s nutcracker has a sharp, sturdy bill. The nutcracker hammers into the ripe cone, which on whitebark pine is closed when mature, to pluck out the seeds. 

The Clark's nutcracker uses it long, sharp bill to hammer open ripe cones to obtain seeds 

The Clark’s nutcracker doesn’t carry one seed or even two seeds at a time back to its home range when foraging. Instead, the nutcracker has a pouch beneath its tongue that can hold between 30 to 150 seeds. Once full, the nutcracker flies back to its home range to cache the seeds.

Caches can be in a trench in the ground, in crevices of bark, among tree roots, near fallen logs or branches, or next to rocks. To minimize spoilage and raiding of a large cache by competitors (such as squirrels), the nutcracker places one to 15 seeds in each cache. 

Snow covers the caches on or beneath the soil, so nutcrackers cache more seeds in above ground locations for access during the winter. For the caches beneath the soil, the nutcracker uses it bill to swipe away soil to create a trench. Then it places a few seeds in the trench and pushes soil back over the seeds with its bill. 

With an amazing memory, Clark’s nutcrackers can remember the location of the caches for nearly nine months--long enough for the first cones to ripen the next summer. If cached in a suitable location, the forgotten seeds will germinate and grow. 

Clark's nutcrackers live in alpine and subalpine habitat

The caches of seeds enable the Clark’s nutcracker to court in January or February when most birds are just trying to survive winter. They lay eggs in March (earlier than any other songbird species) with both the male and female incubating the eggs. The male even develops a brood patch on its chest like the female to keep the eggs warm. When a parent isn’t incubating, it goes off to retrieve seeds from one of its caches.

Once the eggs have hatched, the parents utilize the seeds from their caches to feed the young. Researchers speculate that the early nesting allows the young enough time to mature so they can be ready to cache their own seeds once the cones are ripe in late summer. 

Note: Published in the Bonners Ferry Herald on Feb. 13, 2014.