Bird nests range from simple to elaborate

Just when I think the robin can’t hold any more grass in its beak, it leans over and picks up one more piece before flying to a nearby tree. Without any guidance, the robin knows exactly what materials to collect to build its nest and how to construct its nest. 

Nests are not random creations because all birds of one species tend to build the same type of nest with similar dimensions and materials. For example, American robin nests are deep cups constructed of mud and grass usually in the fork or crotch of a tree. There are exceptions like robins nesting on rail fences or in wood sheds but you wouldn’t find a robin nesting on a gravel bar. 

A cedar waxwing nest is hidden from view

Birds instinctively know how to construct a nest and where to construct it. Nests can be as simple as a scrape in the dirt to massive aeries weighing two tons. No matter the nest, they all serve the same purpose--keep the eggs and hatchlings warm and safe from predators.

The simplest form of nest is the scrape which is a small area cleared for eggs. Scrape nests are used by most shorebirds, terns, many ducks, pheasants, quail and some falcons. Terns and killdeer make a scrape nest among small rocks and rely on the speckled eggs to keep them camouflaged from predators.

A simple type of nest is a cleared area for eggs such as this killdeer nest

Arctic terns lay their eggs among small rocks without any other material

Mallards also use scrape nests but often line it with grasses or other soft materials. Many birds line their nests with soft materials for the eggs and hatchlings.

However, some birds don’t even clear an area for a nest. Some raptors and owls just lay their eggs in a safe place, such as on isolated ledges or in small caves on a cliff. Their eggs are often pointed so they roll in a circle instead of rolling off the ledge. 

The most common type of nest is the cup nest. Most songbirds, hummingbirds and swifts build cup nests. Cup nests are built with pliable materials, such as grass, to make a well-insulated nest. Robin nests are a familiar cup nest as well as barn swallow nests. 

A cup nest that has fallen out of a tree

The middle layer of a robin’s nest is mud and is shaped just right by the female sitting in the partially constructed nest and rotating her belly around while the mud is still moist so it can be smoothed and shaped. 

Barn swallows also use mud to build their nests but their nests are made of mud pellets mixed with grass, straw or hair and then attached to a vertical surface. Collecting mud is no small feat and one barn swallow made more than 1,200 trips to construct its nest. Swallows then line the nest with feathers or hair. 

Hummingbirds build the tiniest of cup nests using fine plant material held together with spider silk. As if the small size wasn’t enough to make the nest hard to find, hummingbirds camouflage the outside of the nest with moss or lichen. 

Often cup nests aren’t seen until the leaves fall off the tree or shrub. Most cup nests succumb to the elements over the winter and some of the materials may be utilized the next spring when most songbirds build a new nest (though some birds, such as robins, may reuse their nests). 

Winter weather slowly deteriorates bird nests

Other types of nests are reused more often than cup nests, including those of eagles and woodpeckers. Look in next week’s column to find out about these nests and other types of bird nests. 

Caterpillars utilize a variety of tactics to stay alive

As a slow-moving, plump morsel, caterpillars are an ideal target for a predator’s meal. However, caterpillars still exist because they have developed means to escape detection from predators or ward off predators.

Black swallowtail caterpillars use black and yellow coloration to warn predators of their toxicity

The most common way caterpillars, like many other animals, escape detection is camouflage. Their camouflage makes it hard for even us to find them when they resemble twigs, bark, leaves, buds, flowers, fruits and tendrils. Larvae of several swallowtail butterfly even resemble bird droppings--something even birds won’t touch. Others bear false eyespots that resemble snake’s eyes or look like hair balls or small furry mammals.

Another way caterpillars escape detection is by not being exposed. They gain protection by living concealed lives within stems, roots, galls, seeds, wood and other plant tissue. Tent caterpillars build silk tents to help protect themselves from hungry birds. Tent caterpillars also find safety in numbers. 

On the other end of the spectrum are caterpillars that are brightly colored and say “See me!” The black and yellow stripes of the black swallowtail caterpillar are easy to spot in the garden but birds have learned to avoid them. The bright colors are a warning to alert predators of the unpleasant taste or toxicity of the caterpillar. Black and yellow are two of nature’s most widespread warning colors as demonstrated with wasps and bees. 

Monarch butterflies advertise their distastefulness with their black and orange coloration. They obtain this distastefulness during their larval stage when the caterpillar eats milkweed and retains the toxins. 

Caterpillars can either obtain their toxicity from the plants they eat or they can manufacture the toxic compounds themselves.

Bristles and hair protect some caterpillars from predators

If taste isn’t bad enough, one caterpillar wards off predators with its bad breath! The tobacco hornworm dines on nicotine-containing plants and as a result has bad breath which keeps predators at bay. 

Predators also tend to pass over caterpillars with hair or bristles--who would blame them. While some caterpillars are just hairy, like the woolly caterpillar, others have spines and barbs. Some caterpillars have urticating hairs which are hollow hairs that discharge a painful irritant when broken. The urticating hairs even cause irritation on curious humans. 

Some caterpillars use multiple tactics, such as hair and colors, to deter predators

Bristles and hair also deter parasitizing insects from laying eggs within the caterpillar and then upon hatching eating the caterpillar’s insides. The hair and bristles act as an armor against these insects since they seek out the caterpillar by smell. 

If smell, coloration, bristles and hair don’t ward of predators, caterpillars often resort to thanatosis--playing dead. Have you ever touched a caterpillar and it has fallen to the ground? The caterpillar is playing dead and is hedging bets that if it remains motionless on the ground it may go undetected. 

Caterpillars exhibit a wide array of physical, chemical and behavioral tactics to avoid being eaten. However, predators keep adapting their search techniques to these tactics and help keep the caterpillar population in check.

Spring wildflowers bring first splash of color

As the weather warms, signs of spring are everywhere--green grass, emerging larch needles and spring wildflowers. The burst of color from spring wildflowers is a welcome sight after winter. 

There are several wildflowers to look for as the snow melts and the days become warmer in North Idaho, most notably the western trillium, western spring beauty, violets, yellow bells and yellow glacier lilies. 

Yellow glacier lilies and western spring beauty

Whether they bloom in early, mid- or late April depends on the weather but these five are usually the first wildflowers emerging. Depending on elevation, however, they can be found as late as midsummer in the high mountain meadows. 

These five wildflowers are the beginning of a palette of color that will paint the woods, mountain meadows and hillsides over the next several months.

Western white trillium (Trillium ovatum)

The western white trillium is one of the first wildflowers to emerge in the woods which is why it is often called the wake-robin. 

Western white trillium

The ‘tri’ in trillium is one way to remember the identifying characteristics of the trillium since all the major parts come in three-- three leaflets, three sepals and three petals. The single white flower sits above the three broad leaves and the three green sepals alternate with the three petals. After fertilization or as the flower ages the petals turn pink.

Trilliums add a splash of color to stream banks, open and deep woods, and other moist shaded areas. 

The petals of the trillium turn pink with age or fertilization of the flower

Western spring beauty (Claytonia lanceolata)

Soon after the snow melts on open, moist grassy slopes, the spring beauty will emerge. The white dime-sized flower sits atop a two- to six-inch tall stem. Pink veins adorn the five petals that are notched at the tip. 

Western spring beauty

While they may be pretty, the spring beauty is also an important spring food source for black bears, grizzly bears and burrowing rodents. Each plant has a carbohydrate-rich corm (a spherical portion of the stem underground about the size of a marble) that these mammals dig up and eat. 

A spring beauty with intense pink veins

Violets (Viola sp.)

Violets are another small flower that add color to moist woods and meadows. All violets have five petals with one petal developing into a spur-like pouch.

There are several species of violets in the region identified by the flower’s color. The stream violet (also called the yellow wood violet or yellow violet) is yellow. The round-leaved violet is lemon-yellow to gold. The Canada violet is white with a yellow base while the kidney-leaved violet has pure white flowers. The early blue violet ranges from blue to deep violet.

Round-leaved violet (Viola orbiculata)

Yellow bell (Fritillaria pudica)

As the name implies, the yellow bell is a small, bell-shaped yellow flower that droops from the stem. The yellow bell is also called goldcup or yellow fritillary. The yellow bell appears in meadows and open woods including open ponderosa pine forests. 

Yellow bell

As a member of the lily family, the flower is three-parted. Like most lily species the petals and sepals of the yellow bell are so similar that the flowers appear to have six petals.

The yellow bell also has a starchy corm sought after by grizzly bears, black bears, pocket gophers and ground squirrels.

Yellow glacier lily (Erythronium grandiflorum)

Painting mountain meadows with a carpet of yellow after the snow melts is the yellow glacier lily, also called the snow lily, fawn lily, dogtooth violet and avalanche lily. The yellow glacier lily is often found at the edge of retreating snowbanks taking advantage of the moisture. Often the glacier lily is intermixed with the western spring beauty.

The single golden-yellow flower droops down with the petals curving backward and the red or yellow anthers hanging below.

Mountain meadow filled with glacier lilies

Yellow glacier lily

Great blue herons more than excellent fishers

Standing motionless in stagnant water, a great blue heron’s head suddenly reels forward into the water and emerges with a small fish. Great blue herons are known for being excellent fishers. Their stealth and lightning-fast strike enable them to sneak up on prey. 

A great blue heron is poised to strike prey with its S-shaped neck

Several features help herons forage effectively. Their long legs enable them to wade into deeper water than other shoreline birds. They can stand still for long periods of time waiting for a fish to come into range or walk very slowly to stalk prey. 

When a fish is within range, their S-shaped neck allows them to quickly strike prey. Specially-shaped vertebrae allow herons to curl their neck in preparation to strike or while in flight (a helpful identification characteristic). 

For their impressive size of 38 to 54 inches tall, great blue herons only weigh five to six pounds

Depending on the size of the fish, the heron strikes in one of two ways. For small fish, herons grab the fish between the mandibles of its bill. For large fish, herons stab the fish with their sharp bill. They then shake the fish to break or relax the sharp spines before gulping down the fish whole. 

Despite their narrow-looking neck, herons can swallow large fish. Since they swallow fish whole, herons regurgitate the solid waste (bones, scales) in the form of pellets similar to how owls regurgitate pellets. 

Another adaptation for eating fish is the special feathers on their chest to help clean fish before they eat them. Herons rake the powder down feathers with their feet to shake off a powder that causes fish slime and oil to clump. This enables the heron to brush off the clumps with its foot before eating it. Herons also rub this powder on their belly feathers to repel swamp slime. 

Even though herons are known as excellent fishers, their diet is highly variable. They also feed on frogs, salamanders, snakes, small birds, small mammals, crayfish, dragonflies and grasshoppers. One study in Idaho found that voles comprised 24 to 40 percent of a heron’s diet. Voles are a major potion of a heron’s winter diet because the shallow, calm water they feed in is often frozen. 

Herons look for food, such as voles, in grassy areas

Their variable diet is one reason the great blue heron is the most widespread heron in North America. In some areas the heron resides year-round but in northern areas herons migrate south unless there is a reliable food source. 

Whether they are permanent residents or migrants, great blue herons are noticeable in the spring when they are nesting because of their noisy ruckus. Herons are solitary when they hunt but they nest in colonies. The heronries can include up to 500 nests in areas with plentiful food and nesting sites but typically range from a few to several dozen nests. 

Herons build their nests high in trees if trees are available otherwise they build them among grass on islands. In Idaho and Montana, herons favor cottonwood trees along rivers and lakes but they will also nest in the tops of ponderosa pine and willows. 

Heronries can consist of a few nests to several hundred nests

They build large, stick platform nests with the male bringing material and the female placing the items. Herons will often reuse nests and the oldest nests are the largest--sometimes up to four feet across. 

Like most animals, herons are most vulnerable when young with 69 percent dying before they are a year old. Eagles, raccoons, bears, turkey vultures and red-tailed hawks are a few predators of great blue heron young. If a chick or an adult is killed within a nesting colony the other birds will often abandon the colony. 

Once the young fledge, they return to the nest to be fed for up to three weeks, placing great demand on their parents’ fishing skills.

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.