Wednesday, February 25, 2009

Aquatic Plants & Animals

Nature Watch
February 25, 2008

By Susan Benson,CNHM Director of Education

Water is the coolest thing! It is the only natural substance that can become a solid, liquid, or gas. Water is colorless, odorless, and tasteless. It is the most abundant molecule on the Earth, covering about 70% of the Earth's surface in liquid, solid, and gaseous states. Up to 60% of the human body is water - the brain is 70% water, our blood is about 83% water, and our lungs are nearly 90% water. Oceans contain 97% of surface water, glaciers and polar ice caps have 2.4%, and the remaining 0.6% is found in other land surface water such as rivers, lakes and ponds. It is no surprise that humans in the north woods end up spending so much time on our lakes and rivers. Even in the winter, how can we stay away? The glistening snow, the serenity of the view, and the life still below is almost magnetic for many of us.

What happens to the water in the winter? First let us rewind in time to summer, when warm water is found at the surface while cooler water sinks to the bottom. Autumn winds tend to mix up the water and the lake “turns,” so that winter waters are warmer near the bottom where the fish hang out, and colder water is nearer the surface where the lake freezes.

Let’s take a closer look at this phenomenon. As the lake water continues to cool, unlike other substances, it maintains a maximum density at 39 degrees Fahrenheit. After water reaches this temperature, it becomes lighter and stays on the top of the lake surface where it converts to ice. Once the first thin layer of ice is frozen, wind cannot disturb the deeper water, causing the temperature to stay at the same temperature throughout the winter. This ice layer becomes a cap on the ecosystem, limiting the amount of nutrients, energy, and oxygen that can enter the lake. After these events occur, the lake residents living on or under the ice function and survive within a very small range of temperature that brings about some interesting changes.

For cold-blooded fish and aquatic invertebrates that cannot control their body temperature, their bodies maintain the 39 degree temperature. Their metabolism slows, allowing them to conserve more oxygen and energy. Although still very sluggish, they can react to their surroundings. These adaptations have some benefits, but there are still dangers in winters when there is low snow cover and extended cold, causing the water begins to freeze to the bottom, or when the amount of oxygen becomes depleted.

Reptiles and amphibians that hibernate in the bottom mud use oxygen all winter long, and since they are heavier users of oxygen, the oxygen in a body of water is first depleted near the bottom. Local ice fishermen are probably aware of the fact that fish species rise in the water as the winter continues – as a reaction to this lack of oxygen in the lower areas of the lake. Aquatic plants also deplete the amounts of oxygen through respiration, but fortunately, there are some plants that can still photosynthesize in such extreme low light levels.

Semiaquatic animals also have some adjustments to make to the winter lake changes. Muskrats compensate for any heat loss from the cold water by continual grooming themselves with oily secretions. Beavers have a special means of reducing heat loss from their bare tails and feet. Other animals have special fur adaptations to deal with the cold water conditions.

In spring, the lake will “turn” again, causing the warm water to rise, and the annual cycle to keep going. Right now we can feel the daily sun getting warmer, or observe the snow melting daily off our roof even when air temperatures are not as warm. For us, spring might seem just around the corner. Another thaw and spring melt might bring smiles to our faces in upcoming weeks, but the lake’s sealed lid will be slow to release the aquatic ecosystem for some time to come.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at to learn more about exhibits and programs.

Wednesday, February 18, 2009


Nature Watch
February 18, 2009

By Susan Benson,
CNHM Director of Education

While I continue to keep warm with my furnace and new comforter, a black-capped chickadee has a number of amazing adaptations for staying warm throughout the winter that far surpass my own. For a bird that rarely lives more than thirty months, winter is a most challenging time for a chickadee that weighs less than my favorite chocolate bar or a few paper clips (one-half an ounce.) Food, brain, feathers, and body work together to keep this backyard bird favorite alive.

Chickadees eat mostly insects, fruits and seeds. During the winter they consume about ten percent of their body weight daily, which means they have to eat, a lot, all day long. In the fall, a chickadee's brain changes as their hippopocampus expands, improving their memory ability. During this time, they stash seeds in pre-selected roost cavities, and months later can recall where those sites are located. In the winter, a time when fruit and insects are scarce, they alter their main food source to the more abundant coniferous seeds, a food high in oil and fat content. Chickadees have even been observed taking fat from previously scavenged dead animals, which serves as an excellent source of calories. Some food chickadees eat is chemically changed into energy reserves that are stored for heat energy at night. By morning, when those reserves are used up, they get chilled and need to eat again, which is why chickadees frequent bird feeders so often in the morning. A study in Wisconsin has shown that birds depending upon bird feeder sunflower seeds do not survive better than those who do not. However, scientists discovered that when winter temperatures are lower than ten degrees, chickadees that access bird feeders can double their survival rate compared to chickadees without feeder seed availability. Although we can certainly appreciate our simplicity of one-stop shopping at our local grocery store as preferable to the food gathering life of a chickadee, we can at least envy their ability to pig out daily without gaining any weight.

While we discuss the R-value of our home's insulation, a chickadee produces more feathers for warmth throughout the winter. The outer feathers have hooks called barbs that zip together to create a wind barrier, while the under feathers are down, which when fluffed, could be considered a human homeowner’s dream because of its insulation value. As a chickadee fluffs its feathers to create an inch-thick coat, they can maintain a temperature of over 100 degrees Fahrenheit (F.) even when outdoor temperatures are at zero degrees (F.). Certainly our reliance on down feathers in winter coats is a tribute to our feathered friends and their ability to survive cold weather conditions.

While hypothermia is a status which humans avoid, chickadees experience it almost nightly when temperatures are very cold. Although their normal daytime temperature is 108 degrees (F.) they regulate their body by decreasing it fourteen to eighteen degrees (F.). This ability to "turn down the thermostat" allows chickadees to conserve twenty-five percent or more of their hourly energy expenditure. As the night cools, their chest muscles also begin to shiver in order to generate heat. Their friendly social nature as they stick together in flocks during winter is also an advantage. They can roost together in tree cavities to share body heat and save energy. During extreme cold, they might not leave their roosts at all. Finally, another body adaptation is related to their bare feet. Chickadees slow down the blood circulation to their feet just enough to keep these extremities from freezing, bringing a whole new meaning to the idea of "cold feet." This combined set of adaptations, although not exclusive to chickadees alone, is amazing!

Whether you are hearing the spring "fee-bee" of a chickadee in your yard, or observing a fluffed up bird through the window at your feeder, these birds can surely be appreciated and enjoyed. Next time you fill your feeders, you can be assured that you are contributing to the successful survival of many of your backyard birds. Perhaps you enjoy them for their ability to thrive in any condition, for displaying a continuous show of beauty, an acrobatic flight or their curious behaviors and activities. Whatever the reason we appreciate them, we can find many positive abilities in a chickadee that could be a model for human behavior.

Wednesday, February 11, 2009


Nature Watch
February 11, 2009

By Susan Benson,CNHM Director of Education

The smell of spring is in the air. I went for my first above zero temperature walk this weekend along the Namekagon River, and it was delightful feeling the sun on my face. I heard the sound of the blue jays, pine siskins, and evening grosbeaks. At the Museum’s Nestel property, I saw the most amazing cluster of fox tracks, bedding areas, and territory markings, everywhere in the parking area. Most exciting to me was hearing my first chickadee spring mating call.

"Fee bee ee" or "Hi, sweetie" is indeed the sweetest sound heard from chickadees throughout mid- to late-winter. Black-capped chickadees have a very sophisticated communication system that has over thirteen different vocalizations. According to research, the fee-bee song production increases once in the winter and once in the spring, and occurs almost exclusively at dawn, usually beginning in late December and then again later in the spring. Most fee-bee songs are sounded by males, typically from a perch at a distance from other birds. In addition to being used for mating purposes, chickadees will also sound this “sweetie” call when leading a flock, or to advertise their territory to keep their rivals away.
Research has shown that chickadees use variations of the “chick-a-dee-dee” call as they spot a lurking predator. Having tested fifteen predator species, researchers discovered that chickadees vary the call depending on how dangerous the predator might be. The greater the danger, the more “dee” syllables they add at the end of the “chicka”. When facing stationary predators, chickadees will voice the “chickadee” variation and sometimes mob together to harass the threat. When playing recordings of these varied alarm calls to chickadee flocks, researchers received mild or intense responses from those birds depending on the alarm call played. Surprisingly, great horned owls are not considered threatening because they are bigger and slower to a speedy chickadee.

There are other chickadee vocalizations, and listening to their voices gives the observer a peek into the complexity of chickadee behavior. If intrigued, it would also be worth trying to observe behavioral patterns such as postures and facial expressions in which chickadees participate. No further research is necessary, though, to enjoy the company of these wild backyard neighbors. Listen and look for this first taste of spring, not influenced by thoughts of the groundhog seeing his shadow, but by other signs nature has bestowed upon the north woods.

Chickadee Calls and Songs
“Chick-a-dee-dee”: Both sexes use this call to advertise a good food source, to signal "all is safe" when danger has passed, or to help separated flock mates find each other.
Added “dees”: Added at the end of “chick-a-dee” calls to alert others to danger.
The "Fee bee ee": These notes may be given before or during mating.
The “Tseet: A quiet, high note said regularly when a chickadee is undisturbed, and stops immediately when the bird is disturbed.
The “See”: Said quickly when they spot a predator, and then quickly flee.
The Gargle, or Ch'dle-ee: A call that occurs during territory disputes; there are at least fifteen gargle-type sounds.
Begging Dee: Young chickadees use this call when they see adults after they have left the nest as a way to say "feed me! feed me me!"
Broken Dees: Nesting females use this to ask their mates to bring food.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at to learn more about exhibits and programs.

Wednesday, February 4, 2009

Animals & Heat Loss

Nature Watch
February 4, 2009

By Susan Benson,
CNHM Director of Education

As I mutter about the cost of heating in my home this winter, I am at the same time reminded to be grateful for this heat. I cannot imagine what it would be like to be outdoors all winter long in these continual, below zero temperatures. If one ponders all of the ways that an animal can lose heat, it is astonishing that they can survive at all. For anyone who has studied physical science, they might recognize the terms convection, radiation, conduction, or evaporation, which are some of the challenges animals in our region face in the winter.

One way heat can be transferred away from an animal’s body is through conduction, in which an animal loses heat from their skin to the air, or from their foot surface to the ground. When temperature differences between an animal and its surroundings are greater, heat is conducted much more quickly. Animals with dense fur or more air in their fluffed up feathers conduct less heat into the surrounding atmosphere.

Moving air or wind can cause convection to occur as the wind takes heat away from animal’s bodies, but has a smaller impact when the thickness of an animal’s fur is greater. Animals can also lose heat through radiation, similar to a radiator in our house. We can lose heat to evaporation through our exhaled breath, or when animals sweat. The idea of putting plastic bags around your socks in winter has merit, as it keeps the warm water vapor from escaping, so although your feet get wet with perspiration, they still stay warmer. Studies have shown that radiant heat loss amounts to ten percent or less of an animal’s total energy loss, and so is disregarded as a significant factor in heat loss.

How do animals cope with these -22 degree nights? Animals can huddle together to decrease the surface area of their exposure. By increasing the thickness of the underfur as insulation, a deer mouse can increase its insulation by one-third in the winter. Many mammals increase the thickness of their fur behaviorally by raising their hairs, and birds fluff their feathers, trapping more warm air closer to their bodies. Some animals curl their extremities closer to their bodies. By sharing their lodges, beavers can keep the internal temperature above freezing. Many small mammal species (least shrews, meadow voles, and white-footed mice) that are solitary during the summer live together in social communes during the winter in nests under the snowpack. One vole species that had as many as ten individuals in one nest was found to be twelve degrees warmer than ground temperatures and up to twenty-five degrees warmer than air temperatures. Some small birds go through a controlled hypothermia every night, decreasing their body temperature a few degrees and reducing their heat flow.

Whatever way an animal copes with our winter cold, I continue to admire their abilities. I appreciate my insulative ability of my winter coat, hat and mittens that allow me to enjoy outdoor activities. Still, I wouldn’t trade it for what our animal friends have been exposed to this winter.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at to learn more about exhibits and programs.