Nature Watch
December 27, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
I saw the first white snowshoe hare of the season today. I was walking down near the Namekagon River when I noticed this white lump just inside the tree line along the road. There were still a few brown spots on the shoulder and back, but the hare had otherwise changed over to his beautiful, pure white winter coat that will eventually help it to disappear against the winter snow.
The change in fur color from brown to white in the fall and back again in the spring is just one difference between hares and rabbits, but it is the most easily observed. Because of this unique transition, the snowshoe hare is also known as the “varying hare.” Why do hares molt this way and rabbits do not? The answer is mostly related to climate.
The geographic ranges of hares and rabbits overlap here in Wisconsin, but hares are considered a northern species, while rabbits are a southern species. Farther north, the durations of summer and winter are more equal, so hares change colors to match their environment. The same is true of other far northern species, such as the weasels (which are also found in Wisconsin), ptarmigan, arctic fox, and collared lemmings. But the change in color has to also keep the hare warm, and white is typically known as a color that reflects sunlight. The answer to this riddle is that white in the natural world is not a color but is the absence of color, or pigment. The cells in white hairs are empty of pigment and are instead filled with air, which provides thermal insulation. The change from brown to white fur begins as the amount of daylight decreases. The ears and feet are the first to change, and the whole animal is white after about 10 weeks.
Snowshoe hares (waabooz in Ojibwemowin) are found in the northern half of Wisconsin where they prefer spruce and cedar swamps and other thickly-vegetated coniferous woodlands. Up to two litters of one to seven (usually two to four) hares are born each year between May and August. Hares primarily feed on grasses, tree buds, and other plant material, but they are also known to feed on the meat of dead animals, including other hares. They do not kill other animals, but they will scavenge carcasses whose insides have been exposed. Main predators of snowshoe hares in Wisconsin include weasels, gray and red foxes, coyotes, wolves, bobcats, and mink.
A popular topic of study for biologists has been the dramatic fluctuations of snowshoe hare populations. Hares are known to go from periods of great abundance (almost overabundance) to periods when there seem to be none left anywhere. The severity of the fluctuation varies geographically, and this is thought to be caused by the relative number of other species that occupy the same level as the hare in the food chain. In other words, if there are fewer links in the food chain (such as in far northern latitudes), and the hare is a main source of food for larger predators, than over-consumption by predators can cause the hare population to decline sharply, and the predator population will soon follow. On the other hand, if there are other animals (such as cottontail rabbits here in Wisconsin) for predators to feed on, then the hare population does not change so dramatically. It is estimated that as many as 85% of hares do not live for more than one year. The common life span for those that do survive is five years.
The change of seasons is upon us. The varying hare has shown that winter is indeed on the way, even if we do not see much snow yet. But the lack of snow makes it easier for us to see this fascinating animal if we look hard enough.
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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
Thursday, December 27, 2007
Friday, December 21, 2007
This Food is for the Birds
Nature Watch
December 21, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
I returned home late one evening last week and was walking up to the house when I heard it. Actually, I felt it more than I heard it. There was a deep resonant sound that beat in my chest. I stopped. It was about 25-degrees, and my breath formed small clouds as I stood in the driveway listening. Then, from out of the forest came a deep voice: Who’s awake? Me too. A quieter, single-note response followed from a second bird and then the silence returned. The male owl repeated his question and answer: Who’s awake? Me too, and the female bird responded again with a single note. After listening for a few minutes, I went into the house. It was clear that this conversation between a pair of Great Horned Owls would continue for a while.
There are eight species of owls that nest in Wisconsin, but only about half of them can be found in Bayfield County. The Great Horned Owl is perhaps the best known of these because it is found in every Wisconsin county, and because it is the most “owl-looking” owl. Even if people don’t know this common species by name, they likely think of it whenever someone says the word “owl.”
Great Horned Owls are large birds, nearly two-feet tall, with yellow eyes and feather tufts that stick up on each side of the head like ears. In our area, only the Barred Owl comes closest in height, standing 21-inches high. But Great Horned Owls can be distinguished from Barred Owls by their eyes. Barred Owls are one of only four species that have dark brown eyes rather than the piercing, bright yellow eyes found on the Great Horned and 14 other owl species in North America.
I heard the Great Horned Owls calling that evening because these dark nights and cold days of winter are the beginning of the mating season for them and most other owls. Adults are calling back and forth to each other, looking for mates and cementing relationships. They will soon be building nests and settling down to lay eggs and raise young. In Wisconsin, eggs are laid as early as February 6, and the first young are hatching a little over one month later.
Habitat for the Great Horned Owl varies from the deciduous woodlands between open grass- and croplands, to gaps within the heavily wooded northern forest. They feed on a wide variety of small birds, mammals, and snakes, but their favorite foods are mice and cottontail rabbits. Nests are typically made of large sticks, but the owls do not build a nest themselves. Instead, they will take one over that has been built by some other bird, usually Red-tailed Hawks, but sometimes ravens or the occasional squirrel. The Red-tailed Hawk nests are particularly favored because the hawks migrate and do not return before owl nesting begins. Great Horned Owls also nest in tree cavities and stumps, and even occasionally (but rarely) on the ground.
Great Horned Owls, like most of their other relatives, are most active at night. With a bit of searching, you might find one roosting high in a tree during the day, often sitting right next to the trunk. I once found one in Ashland’s Prentice Park, perched among the bare branches of an aspen tree. I could see its yellow eyes clearly burning right into me even from the great distance that separated us.
If you are fascinated by these birds like I am, you might want to join me on one of the “Owl Prowls” sponsored by the Cable Natural History Museum. One evening a month from June through October, I take people out into the woods to call for owls. Usually we only see Barred Owls, but we are sometimes lucky enough to find a Great Horned Owl or perhaps one of the more uncommon species such as the tiny Northern Saw-whet Owl. Incidentally, if you would like to hear an exchange between a male and female Great Horned Owl like the one I heard a few nights ago, you can find a recording from California on online at www.owling.com/Great_Horned.htm#recordings. Click on the recording labeled “Silverado Canyon, California, October 2000” on the far right. You can also hear the Great Horned Owl and the other species found in Wisconsin at the Museum’s Owl Booth, which is part of our “Birds in Focus” exhibit. Stop in and listen to “who’s awake?” and “who cooks for you all?”!
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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
December 21, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
I returned home late one evening last week and was walking up to the house when I heard it. Actually, I felt it more than I heard it. There was a deep resonant sound that beat in my chest. I stopped. It was about 25-degrees, and my breath formed small clouds as I stood in the driveway listening. Then, from out of the forest came a deep voice: Who’s awake? Me too. A quieter, single-note response followed from a second bird and then the silence returned. The male owl repeated his question and answer: Who’s awake? Me too, and the female bird responded again with a single note. After listening for a few minutes, I went into the house. It was clear that this conversation between a pair of Great Horned Owls would continue for a while.
There are eight species of owls that nest in Wisconsin, but only about half of them can be found in Bayfield County. The Great Horned Owl is perhaps the best known of these because it is found in every Wisconsin county, and because it is the most “owl-looking” owl. Even if people don’t know this common species by name, they likely think of it whenever someone says the word “owl.”
Great Horned Owls are large birds, nearly two-feet tall, with yellow eyes and feather tufts that stick up on each side of the head like ears. In our area, only the Barred Owl comes closest in height, standing 21-inches high. But Great Horned Owls can be distinguished from Barred Owls by their eyes. Barred Owls are one of only four species that have dark brown eyes rather than the piercing, bright yellow eyes found on the Great Horned and 14 other owl species in North America.
I heard the Great Horned Owls calling that evening because these dark nights and cold days of winter are the beginning of the mating season for them and most other owls. Adults are calling back and forth to each other, looking for mates and cementing relationships. They will soon be building nests and settling down to lay eggs and raise young. In Wisconsin, eggs are laid as early as February 6, and the first young are hatching a little over one month later.
Habitat for the Great Horned Owl varies from the deciduous woodlands between open grass- and croplands, to gaps within the heavily wooded northern forest. They feed on a wide variety of small birds, mammals, and snakes, but their favorite foods are mice and cottontail rabbits. Nests are typically made of large sticks, but the owls do not build a nest themselves. Instead, they will take one over that has been built by some other bird, usually Red-tailed Hawks, but sometimes ravens or the occasional squirrel. The Red-tailed Hawk nests are particularly favored because the hawks migrate and do not return before owl nesting begins. Great Horned Owls also nest in tree cavities and stumps, and even occasionally (but rarely) on the ground.
Great Horned Owls, like most of their other relatives, are most active at night. With a bit of searching, you might find one roosting high in a tree during the day, often sitting right next to the trunk. I once found one in Ashland’s Prentice Park, perched among the bare branches of an aspen tree. I could see its yellow eyes clearly burning right into me even from the great distance that separated us.
If you are fascinated by these birds like I am, you might want to join me on one of the “Owl Prowls” sponsored by the Cable Natural History Museum. One evening a month from June through October, I take people out into the woods to call for owls. Usually we only see Barred Owls, but we are sometimes lucky enough to find a Great Horned Owl or perhaps one of the more uncommon species such as the tiny Northern Saw-whet Owl. Incidentally, if you would like to hear an exchange between a male and female Great Horned Owl like the one I heard a few nights ago, you can find a recording from California on online at www.owling.com/Great_Horned.htm#recordings. Click on the recording labeled “Silverado Canyon, California, October 2000” on the far right. You can also hear the Great Horned Owl and the other species found in Wisconsin at the Museum’s Owl Booth, which is part of our “Birds in Focus” exhibit. Stop in and listen to “who’s awake?” and “who cooks for you all?”!
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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
Friday, December 14, 2007
December Birds
Nature Watch
Decemeber 14, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
You may have noticed that the cold weather tends to dampen our cars’ fuel efficiency, meaning we have to burn more gas in winter than in summer to travel the same distance.
The same holds true for birds that spend winter in the cold north. Birds, like cars, run high-powered engines at hot temperatures—somewhere between 102 and 112 degrees Fahrenheit for most birds. They need a lot of energy to keep those engines burning, and this at a time when food is least available! How do they survive?
Their first goal is energy conservation, and birds go about this in a number of ways.
Birds have multiple layers of feathers that help them withstand the cold and maintain body temperature. When birds fluff up their feathers in the winter weather, they effectively double their feather volume, and this thick plumage traps an insulating layer of warm air next to their bodies. It would be as if your clothes magically changed into a puffy quilt when it got cold.
Feathers, however, do not protect a bird’s bill, legs and feet. Birds’ beaks are made of a hard material similar to their toenails that is not very vulnerable to harm from the cold. Exposed legs and feet, though, can suffer cold damage. This is where a clever adaptation allows many birds to survive the winter months, even when their legs and feet are in the icy water.
Here’s how it works: the large blood vessel carrying warm blood from the bird’s body into its leg separates into many smaller vessels. The vein carrying cooled blood back from the foot into the leg also divides into many smaller veins, which run alongside and between the blood vessels.
The birds move the heat from the warmer blood vessels to the cooler blood in the veins before the blood reaches the bird’s body—a strategy called “counter current heat exchange.” Birds also can condense the amount of blood entering the legs and feet by reducing the size of the arteries. These adaptations can decrease heat loss in legs and feet by as much as 90 percent.
Another trick birds practice is standing on one leg and lifting the other up into their breast feathers to keep it warm. Often you’ll see ducks in winter weather perched on the ground; when they do this, they wrap up their legs and feet in protective, warm feathers.
Additionally, many bird species that winter in the north can lower their heart rate, respiration, and metabolic rates to conserve heat and energy. Chickadees, for instance, drop their body temperatures from 10 to 20 degrees on very cold nights. Other birds wintering south of here, like some doves, swallows, hummingbirds, titmice, swifts, and nightjars, also can enter this state of dormancy, or torpor, to survive an unusually cold winter night.
During the cold winter nights, birds like woodpeckers and other species curl up inside tree cavities for cover and heat. Other birds crowd together in whatever nooks or crannies they find. Some species of birds that inhabit open fields in the winter months will burrow into snow holes to escape the winds and chill.
Of course, even with all these strategies of energy conservation in play, birds need to eat in order to replenish their energy. Fuel efficiency can only take you as far as you have fuel.
Some birds change their menus in winter. A nuthatch, for example, usually eats insects in summer, but changes its main dinner menu to seeds and nuts in the winter.
In a harsh winter, where snow and ice covers sources of seeds and insect larvae are hard to get to, many bids do die of starvation. This, of course, is why winter bird feeders can be so important in our region. If you have a chance, stop by the Cable Natural History Museum and see our exhibit “Birds in Focus.” It features a display of bird feeders, advice on feeding tactics, and many other resources that can help you learn about safely feeding birds through the 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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
Decemeber 14, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
You may have noticed that the cold weather tends to dampen our cars’ fuel efficiency, meaning we have to burn more gas in winter than in summer to travel the same distance.
The same holds true for birds that spend winter in the cold north. Birds, like cars, run high-powered engines at hot temperatures—somewhere between 102 and 112 degrees Fahrenheit for most birds. They need a lot of energy to keep those engines burning, and this at a time when food is least available! How do they survive?
Their first goal is energy conservation, and birds go about this in a number of ways.
Birds have multiple layers of feathers that help them withstand the cold and maintain body temperature. When birds fluff up their feathers in the winter weather, they effectively double their feather volume, and this thick plumage traps an insulating layer of warm air next to their bodies. It would be as if your clothes magically changed into a puffy quilt when it got cold.
Feathers, however, do not protect a bird’s bill, legs and feet. Birds’ beaks are made of a hard material similar to their toenails that is not very vulnerable to harm from the cold. Exposed legs and feet, though, can suffer cold damage. This is where a clever adaptation allows many birds to survive the winter months, even when their legs and feet are in the icy water.
Here’s how it works: the large blood vessel carrying warm blood from the bird’s body into its leg separates into many smaller vessels. The vein carrying cooled blood back from the foot into the leg also divides into many smaller veins, which run alongside and between the blood vessels.
The birds move the heat from the warmer blood vessels to the cooler blood in the veins before the blood reaches the bird’s body—a strategy called “counter current heat exchange.” Birds also can condense the amount of blood entering the legs and feet by reducing the size of the arteries. These adaptations can decrease heat loss in legs and feet by as much as 90 percent.
Another trick birds practice is standing on one leg and lifting the other up into their breast feathers to keep it warm. Often you’ll see ducks in winter weather perched on the ground; when they do this, they wrap up their legs and feet in protective, warm feathers.
Additionally, many bird species that winter in the north can lower their heart rate, respiration, and metabolic rates to conserve heat and energy. Chickadees, for instance, drop their body temperatures from 10 to 20 degrees on very cold nights. Other birds wintering south of here, like some doves, swallows, hummingbirds, titmice, swifts, and nightjars, also can enter this state of dormancy, or torpor, to survive an unusually cold winter night.
During the cold winter nights, birds like woodpeckers and other species curl up inside tree cavities for cover and heat. Other birds crowd together in whatever nooks or crannies they find. Some species of birds that inhabit open fields in the winter months will burrow into snow holes to escape the winds and chill.
Of course, even with all these strategies of energy conservation in play, birds need to eat in order to replenish their energy. Fuel efficiency can only take you as far as you have fuel.
Some birds change their menus in winter. A nuthatch, for example, usually eats insects in summer, but changes its main dinner menu to seeds and nuts in the winter.
In a harsh winter, where snow and ice covers sources of seeds and insect larvae are hard to get to, many bids do die of starvation. This, of course, is why winter bird feeders can be so important in our region. If you have a chance, stop by the Cable Natural History Museum and see our exhibit “Birds in Focus.” It features a display of bird feeders, advice on feeding tactics, and many other resources that can help you learn about safely feeding birds through the 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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
Friday, December 7, 2007
Horns & Antlers
Nature Watch
December 7, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
The nine-day gun-deer season has passed, but hunting continues to dominate conversations around town. Going into supermarkets, hardware stores, or gas stations, you can’t help but hear the stories, and those stories often include talk about antlers and horns. These two terms are often used interchangeably, but they actually are different physical structures. Antlers and horns, like hooves and claws, are both modified parts of the epidermal (skin) layer of mammals, but that is where the physical similarities end.
Horns are grown by both males and females in the family Bovidae (cows, sheep, and goats). They are modified bone covered by a cone-like layer of keratin, or modified hair tissue – the same material that forms our own hair and fingernails. Horns grow above the skull but below the skin, entirely separate structures that do eventually fuse to the skull during development. Horns are not shed each year, but are retained and, for many animals, continue to grow throughout life. Also, horns form a single tine and do not branch out. There is one exception to this rule. The pronghorn antelope (which is in a family separate from the cows, sheep, and goats) has horns that are branched, and it is the only horned mammal that annually sheds the keratin sheath that covers the horns.
Antlers are modified bones that do not have the keratin covering. Male deer, elk, and moose, which comprise the family Cervidae, grow antlers. The one exception to this is the caribou; both males and females of this species grow antlers. They are attached to the skull by way of a short base known as a pedicel. Antlers, unlike horns, are grown and then shed each year as the pedicel loses calcium, weakening its connection with the antler. Growth and development of antlers are controlled by hormones and, in the northern hemisphere, the increasing duration of daylight. The timing of the “drop” in the winter coincides with declining testosterone levels and decreasing daylight.
Antlers also have a covering over them, but it is not a permanent cover like the keratin sheath that grows over horns. The velvet that temporarily covers antlers as they grow is soft hair and skin that contains blood vessels and nerves. Growth of the antler stops and the velvet dies when testosterone levels reach their peak each fall. The velvet is then shed, in large part by the animal rubbing its antlers on trees and woody shrubs. This rubbing also polishes the antlers, which become stained by the blood that once pulsed through the vessels in the velvet.
Both horns and antlers are used by males to establish dominance and thereby gain access to females during the breeding season. Among the horned animals, males and females can be distinguished from one another by differences in the size of the horns. Male horns tend to be thicker at the base, while those on the females tend to be straighter and thinner, which may allow them to be used as a stabbing weapon.
Of course, there is variation among the horned animals, too. The horn of a rhinoceros is not considered a “true horn” because it is composed of epidermal cells and fibers rather than a bony core surrounded by a keratin sheath. The rhinoceros horn also does not grow from the skull, but from the tip of the snout. Giraffes also have horns. Their horns are composed of bone, and they arise from the skull like other “true horns,” but they do so from the rear of the skull rather than the front. Both male and female giraffes have horns, but unlike other horned animals, newborn young have them as well.
So if you are hunting and lucky enough to get a buck this season, or if you happen to find a skull or antlers during a walk in the woods, take a look at these fascinating structures. Compare them with horns (we have a few in the museum you can come and see) and you may be able to see some of the differences between them.
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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
December 7, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
The nine-day gun-deer season has passed, but hunting continues to dominate conversations around town. Going into supermarkets, hardware stores, or gas stations, you can’t help but hear the stories, and those stories often include talk about antlers and horns. These two terms are often used interchangeably, but they actually are different physical structures. Antlers and horns, like hooves and claws, are both modified parts of the epidermal (skin) layer of mammals, but that is where the physical similarities end.
Horns are grown by both males and females in the family Bovidae (cows, sheep, and goats). They are modified bone covered by a cone-like layer of keratin, or modified hair tissue – the same material that forms our own hair and fingernails. Horns grow above the skull but below the skin, entirely separate structures that do eventually fuse to the skull during development. Horns are not shed each year, but are retained and, for many animals, continue to grow throughout life. Also, horns form a single tine and do not branch out. There is one exception to this rule. The pronghorn antelope (which is in a family separate from the cows, sheep, and goats) has horns that are branched, and it is the only horned mammal that annually sheds the keratin sheath that covers the horns.
Antlers are modified bones that do not have the keratin covering. Male deer, elk, and moose, which comprise the family Cervidae, grow antlers. The one exception to this is the caribou; both males and females of this species grow antlers. They are attached to the skull by way of a short base known as a pedicel. Antlers, unlike horns, are grown and then shed each year as the pedicel loses calcium, weakening its connection with the antler. Growth and development of antlers are controlled by hormones and, in the northern hemisphere, the increasing duration of daylight. The timing of the “drop” in the winter coincides with declining testosterone levels and decreasing daylight.
Antlers also have a covering over them, but it is not a permanent cover like the keratin sheath that grows over horns. The velvet that temporarily covers antlers as they grow is soft hair and skin that contains blood vessels and nerves. Growth of the antler stops and the velvet dies when testosterone levels reach their peak each fall. The velvet is then shed, in large part by the animal rubbing its antlers on trees and woody shrubs. This rubbing also polishes the antlers, which become stained by the blood that once pulsed through the vessels in the velvet.
Both horns and antlers are used by males to establish dominance and thereby gain access to females during the breeding season. Among the horned animals, males and females can be distinguished from one another by differences in the size of the horns. Male horns tend to be thicker at the base, while those on the females tend to be straighter and thinner, which may allow them to be used as a stabbing weapon.
Of course, there is variation among the horned animals, too. The horn of a rhinoceros is not considered a “true horn” because it is composed of epidermal cells and fibers rather than a bony core surrounded by a keratin sheath. The rhinoceros horn also does not grow from the skull, but from the tip of the snout. Giraffes also have horns. Their horns are composed of bone, and they arise from the skull like other “true horns,” but they do so from the rear of the skull rather than the front. Both male and female giraffes have horns, but unlike other horned animals, newborn young have them as well.
So if you are hunting and lucky enough to get a buck this season, or if you happen to find a skull or antlers during a walk in the woods, take a look at these fascinating structures. Compare them with horns (we have a few in the museum you can come and see) and you may be able to see some of the differences between them.
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 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.
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