Room to roam: Home range fluctuates with food supply

Fences, stakes and lines on a map define my property from my neighbor’s property. Animal’s have property lines too but they define them differently. 

Some animals, such as coyotes and bobcats, defend their territory by marking the boundaries with scat or urine. This tells other members of the same species this area is occupied.  

Red-winged blackbird 

The harsh scolding of a red squirrel lets everyone in the forest know that someone is intruding on its territory. The puffed-out display of a red-winged blackbird while calling lets another red-winged blackbird know it is intruding. 

Animals establish and defend territories primarily because of food and mates. A territory ensures an adequate amount of food for an animal.

A chickadee will defend a small territory in the summer while breeding but will flock together with other birds in the winter. While flocking together, the chickadee will remain within a certain area, which is considered its home range. 

Chickadees will defend a small territory during breeding season

All animals have a home range but not all have a territory. An animal only has a territory if it defends the area. 

A home range is the area an animal uses regularly to survive. For a beaver that may mean the pond with its lodge and the surrounding forest in which it fells trees. 

Animals move around their home range for food, shelter, to find a mate, care for young and to escape predators. 

The size of the home range depends immensely on food abundance, habitat and the size of an animal. A wolf pack has a smaller home range when deer and elk are plentiful. 

A black bear’s home range will be smaller if it occupies prime huckleberry brush. In North Idaho, a female black bear has a home range of five to 10 square miles, whereas a female grizzly bear ranges from 90 to 100 square miles. 

Food supply dictates the size of a black bear's home range

Carnivores tend to have a larger home range than herbivores because their food source is more spread out. Herbivores, such as deer, feed on vegetation in a their home range. Carnivores, such as wolverines, prey on animals that wander about their own home ranges. Thus, a carnivore’s home range has to cover multiple home ranges of its prey.

Males typically have larger home ranges for mating purposes. A male bobcat’s territory will overlap several female’s home ranges, ensuring that other males won’t mate with the female bobcats in his home range. However, the female bobcat’s home ranges will not typically overlap. 

Unlike a bobcat, female cougar home ranges can overlap, especially when it comes to the young dispersing. A young female cougar will often establish a home range that overlaps her mother’s home range. 

On the other hand, young male cougars may need to travel far to find a home range without a dominant male. 

Traveling to find a new home range can have mixed results. For young wolves, crossing an occupied territory can mean death, an allowance to cross or acceptance into the wolf pack.

When an animal establishes a home range, it becomes familiar with the locations of food, water, hiding spots and danger, such as a road. The animal may have one resting spot or multiple resting spots within its range, depending on the size of the home range. 

The size of a home range or territory can vary year to year or season to season depending on food availability, which is why animals have a more flexible means of marking their territory than we do with fences. 

Note: Published in the Bonners Ferry Herald on Feb. 28, 2013. 

First Robin

Is it too early for spring? The first robin sighting is a hint of what's to come.

Looking back at my calendars, this sighting is two weeks earlier than in 2011, when I saw the first robin on March 9. The first bluebird was on March 13 that year.

Masked bandit commonly strikes at night

Small, five-toed tracks in the snow that are suggestive of miniature bear tracks amble away from an empty dog food dish outside a door--the masked bandit strikes again. Under the cover of darkness, the masked bandit raids what food sources it can find in the winter, including pet food and garbage.

Called a masked bandit because of the black markings on its face, a raccoon is seldom seen in the winter except for their tracks in the snow. 

While their two-to-four-inch tracks may resemble a bear’s tracks in miniature, they don’t sleep away the winter like bears. Instead they only den up when the snow becomes deep or during cold spells. 

Raccoons are similar to bears in the way they prepare for winter. Both acquire layers of fat in late summer and fall to survive the winter. 

Despite the raccoon’s omnivore diet, many of it’s food sources disappear in the winter, so it has to depend on fat reserves to survive. Unless it can find a steady source of pet food or garbage.

During winter, raccoons aren’t likely to find bird, turtle or waterfowl eggs or even reptiles, frogs and insects to eat. 

Raccoons eat almost anything but they are especially fond of food from the water. They often hunt along streams or marshes to find meals of frogs, fish, snails, crayfish, amphibians, aquatic invertebrates and even young muskrats.

When a raccoon catches prey in or near water, it may manipulate it in the water, giving the impression of washing it. However, scientists think that a raccoon’s sense of touch may be better when it’s feet are wet. 

A raccoon’s feet have five long, dexterous digits that enables it to grasp and manipulate objects. The long toes in combination with sharp, non-retractable claws make raccoons good climbers. Like squirrels, they can rotate their hind feet 180 degrees to descend trees head first. 

Raccoons climb trees to rest in during the day, either on a branch or in a cavity. A raccoon’s scat can be found at the base of a climbing tree because raccoons defecate before climbing a tree. Scat can also be found on roofs because they defecate before entering a structure. 

Resting sites can also include an abandoned mammal’s burrow, a building, abandoned vehicle, hollow log or cavity among rocks. Typically a raccoon will be by itself, unless it is a mother with young or it is extremely cold. Groups of 20 raccoons may share a den during a cold snap.

Young will stay with their mother through their first winter. Young raccoons are the most likely to die from starvation in late winter and early spring because they have fewer fat reserves to draw on due to their smaller body size. 

Young raccoons also have to be wary of eagles and large owls, the latter being nocturnal like raccoons. Birds aren’t a raccoon’s only predators. They are preyed upon by cougars, bobcats, coyotes and domestic dogs. 

Being nocturnal and crepuscular (active at dawn and dusk) helps raccoons avoid some predators and is why they reduce their activity on full moonlit nights. Being active under the cover of darkness allows the masked bandit to strike again. 

Note: Published in the Bonners Ferry Herald on Feb. 21, 2013.

Black bear research sends biologists into bear den

“Now! Now! Now!” Tom Radandt exclaimed as he kicked his feet, which was all that could be seen poking out of the black bear den. Immediately he was pulled from the den by the ropes tied to his ankles. 

Biologists ready to pull Radandt from the bear den

As the biologists quickly covered the entrance with a tarp, Radandt explained that the yearling climbed over him as he was getting ready to cut the collar off the female black bear. Retrieving a collar off a female black bear can be exciting when she is sharing a den with two yearlings.

“Den work is always interesting, you never know,” said Wayne Wakkinen, IDFG biologist. 

Radandt, Wakkinen and Justin Teisberg were retrieving the GPS collar as part of a study on black bear habitat around McArthur Lake. Only two of the 16 collars didn’t drop off as scheduled on Oct. 1, so they needed to be manually removed if the bear dens could be accessed. 

“The nice thing with black bears is you can go in the dens,” said Wakkinen. “The bears will be awake when you dig up the den but they will be lethargic. You don’t go into grizzly bear dens. They seem to be more alert and it usually doesn’t go well.”

Preparing the sedation drugs

Biologists use drugs to sedate black bears. They are the same drugs veterinarians use on dogs before surgery explained Radandt. 

If the release mechanism on the collar doesn’t work and you can’t get to the den, the canvas spacer on the collar will eventually rot, causing the collar to fall off, explained Wakkinen. 

The collars are typically scheduled to drop off within two years because that is the battery life of the collar. The GPS-equipped collars record the location of the bear every 60 minutes. Unlike older collars where data could only be downloaded with the collar in the office, the new collars can download data remotely. In this study, Wakkinen used an airplane and telemetry to find the bears every couple of weeks and then circled while the data downloaded onto a computer in the plane. 

Collared retrieved after one yearling tried to escape

The biologists still try to retrieve the collars even though they have the data because they can refurbish them. 

“A lot cheaper to rebuild than to buy new stuff,” said Wakkinen. 

Later this spring when all the data is compiled, Wakkinen will be able to see where the sixteen bears spent their time in regards to habitat. Knowing what type of habitat the black bears utilize will help him make recommendations to the Idaho Transportation Department on where the bears will most likely cross the highway.

The bears in this study were trapped in the spring and summer of 2011 within three miles of McArthur Lake. Wakkinen explained they use leg-hold snares and check the traps once or twice a day depending on the weather. The goal was to trap bears that had an opportunity to cross the highway. 

A concurrent study is taking place at Lookout Pass with the same goal of determining potential highway crossings areas said Wakkinen.

“We don’t have to have the bears cross the highway but if we get highway crossings, all the better,” said Wakkinen. 

Retrieving collars in the fall after they drop-off is usually easier then reaching the den in winter

Black bears have a small home range, roughly five to ten square miles, explained Radandt, USFWS biologist. Therefore, trapping black bears around McArthur Lake provides the biologists a better chance of seeing what habitat they use in the area near the highway.

A female grizzly bear has a home range of 90-100 square miles. Black bears are smaller and don’t need as large of an area for food explained Teisberg, USFWS biologist.

“They are reliant on the huckleberry crop,” said Wakkinen. “They will travel more in bad berry years.”

“The population seems to be stable,” said Wakkinen. “The harvest rate of black bears is surprisingly low. The harvest rate is five to eight percent, maybe 10 percent.” 

In Boundary County, black bear density is approximately one bear per two to three square miles. Over by Priest Lake, the density is closer to one black bear per square mile explained Wakkinen.

Telemetry is used to locate the collar in the den (on the left)

Black bear research has advanced with technology. When the collars first were used the biologists had a good year when 30 data points a year were collected. Now, the GPS collars can provide at least that many data points a day, providing a wealth of information on habitat, density and movements. 

And when technology doesn’t work, it sends a biologist into a black bear den with a sow and two yearlings to retrieve a collar. 

Note: For more information and photos on black bear hibernation and my adventure into a bear den, see post of "Looking inside a black bear den" on January 31, 2013.

Note: Published in the Bonners Ferry Herald on Jan. 31, 2013.

Have you had tree bark for breakfast lately?

How often do you eat tree bark? Every time you sprinkle cinnamon on your oatmeal or eat cinnamon rolls for breakfast. Cinnamon sticks are dried, curled up pieces of bark from Southeast Asian trees of the genus Cinnamomum. 

The cork stoppers on wine bottles--also bark. Cork oaks have thick, corky bark that is harvested by stripping away the bark every decade without killing the tree, similar to birch bark but thicker.

While bark from certain species is useful to people, it is crucial for the survival of a tree. Bark prevents excess water loss, repels insects, protects the tree from temperature extremes and animals, and provides fire protection for certain species. 

From white birch bark to the fibrous reddish strips of cedar, bark is as varied as the leaves on trees. 

Unlike leaves, bark can look different with age. For example, trembling (or quaking) aspen has creamy-white bark with black markings after it grows out of its pale green juvenile bark. Then as the tree matures, the older bark at the base of the trunk can turn gray and become heavily fissured. 

Young aspen tree

To understand how bark becomes fissured with age on some trees, we have to go deeper into the tree. When looking at a stump, such as a ponderosa pine, there is a distinct line between the bark and the wood. Typically there is more wood than bark. 

Bark is only a few inches thick on a grand fir over 150 years old

When a tree grows, it grows from the cambium layer, which is a very thin layer of cells that encircles the tree between the bark and the wood. The cambium layer produces cells to the inside that creates the sapwood and cells to the outside that creates bark. 

The cells created to the outside of the cambium layer are phloem cells, which carry nutrients manufactured by the leaves down to the roots. New cells are created each year, which pushes the oldest phloem cells to the outside. The old cells eventually die and don’t transport nutrients. 

Holding all the phloem cells in is a layer of cork cambium. The cork cambium creates cork cells towards the outside of the tree which is the bark visible on a tree. 

As the tree grows in girth, something has to give, especially since there are dead cells that cannot stretch. What gives are the cork cells. As the new growth pushes outward, the cork cells crack and form fissures and ridges. Thus, fissures form on trees past a certain diameter, which depends on the tree species. 

Since the base of the tree is the oldest, it has the thickest bark and biggest fissures. Thick bark is beneficial to trees, particularly those that grow in fire-prone areas. Sequoia have bark that can be two feet thick. Thick bark often has huge fissures and ridges that create updrafts which carries heat up and away from the trunk. 

The thick bark on a ponderosa pine protects the tree's living tissues from fire

Part of the bark’s protective nature comes from the cork. As the cork cells mature they deposit a waxy material called suberin in their walls and die. The suberin helps the bark be waterproof and air-proof.

Some species’ cork cells are so air-proof that the inside of the tree can’t breathe. The cambium layer and the cells it creates need air from the outside for cellular respiration. To counteract the airtight bark, the tree creates lenticels, which are the horizontal lines on bark, such as on birch. The lenticels act like windows in the bark, allowing for air exchange. 

Bark peeling off birch trees

As a tree matures, the oldest bark can be sloughed off. The ground around the base of a mature ponderosa pine is often covered with puzzle-like pieces of bark sloughed off as the tree grows. 

Animals, such as beavers, moose and porcupines, tend to eat younger bark since it isn't as tough as older bark. They also eat the nutritious cambium layer underneath the bark. No matter how many animal's depend on eating bark to survive the winter, I'll only eat bark in the form of cinnamon, particularly in cinnamon rolls. 

Note: Published in the Bonners Ferry Herald on Feb. 14, 2013.

Happy Valentine's Day!

Do duck’s feet get cold standing on ice?

Staying warm in winter is crucial for animals to survive. Mammals have thick fur and birds fluff their feathers but their legs often have little to no insulation. Keeping extremities warm can be a struggle for animals. But some animals purposely don’t keep their legs warm to save energy. 

The feet of a caribou can be 55 degrees Fahrenheit cooler than their core body temperatures (105 degrees Fahrenheit). A mallard’s webbed feet may only be one degree warmer than the ice it is standing on. 

Caribou don't keep their legs as warm as their bodies when temperatures at near minus 40 F

Cold feet may seem counterintuitive to staying warm but cold feet actually help the animal stay warmer. Cold-footed animals have a special arrangement of arteries and veins in their legs that aids heat exchange and is called countercurrent heat exchange.  

Remember that arteries leave the heart with oxygen-rich blood and veins return oxygen-depleted blood back to the heart.

When an artery leaves the core of the body into an extremity the blood is as warm as the core. As the blood travels to the end of the extremity, which has little insulation, the blood cools down. 

In animals without countercurrent heat exchange (such as people), the cold blood returns to the core and has to be warmed within the core, expending significant energy. 

However, in animals with countercurrent heat exchange (such as birds) the placement of the vein is extremely close to the artery. Close enough that the venous blood can absorb the heat lost by the cooling arterial blood as it flows to the end of the extremity. Remember that heat is conducted from a warm object to a cold object. 

Even near the foot, the cool arterial blood is warmer than the cold venous blood starting to return to the core and still warms the venous blood. As the venous blood moves up the leg, the warmth from the arterial blood becomes greater (because it is closer to the core), thus warming the venous blood even more. 

By the time the venous blood enters the core of the body, it is almost as warm as the outgoing arterial blood. Very little energy is needed to warm the venous blood to the core temperature. 

Countercurrent heat exchange conserves body heat because the warm arterial blood transfers heat to the incoming venous blood. Thus, very little heat is lost to the environment. Mallards lose only five percent of their body heat through their feet when their feet are 33.8 degrees Fahrenheit. 

When geese can't keep their feet from freezing, they tuck one or both feet into their feather to warm them up.

Cool arterial blood still supplies the oxygen the tissues in the legs need and is warm enough to prevent frostbite. 

Many of the animals that spend their time in snow or on ice utilize countercurrent heat exchange to reduce heat loss. Moose and mountain goats are two animals that don’t keep their feet warm. 

Aquatic animals also use countercurrent heat exchange to minimize heat loss. Cold water can drain the warmth of an animal faster than cold air. Turtles and seals use countercurrent heat exchange to supply their flippers with oxygen yet minimize heat loss and beavers use it in their tails.

Even though ducks and geese minimize heat loss by keeping their feet cold, sometimes their feet become too cold. Then they tuck one foot into their feathers to warm it up while they stand on the other foot because sometimes it’s just too cold.

Note: Published in the Bonners Ferry Herald on Feb. 7, 2013.