Nature Watch
September 28, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
After the glory of autumn color comes the inevitable bare-limbed look of our forests as leaves fall from hardwood trees. Ever wonder what triggers those leaves to fall?
It’s due to a chemical called auxin, a growth-regulating substance produced by plants. When leaves develop in the spring, each new leaf makes large amounts of auxin, which among other things, signals the leaf stem to grip its branch tightly. As the leaves age, they produce less auxin. As summer wears on, two thin layers of cells called the abscission layer grow across the base of the leaf stem where it is connected to the branch; this is likely initiated by the decreasing daily light period.
As the supply of auxin dwindles, the cells in the abscission layer separate from one another, and the leaf stem’s hold on the branch grows weaker. A hard rain or a gust of wind then blows the leaf free and it falls to the ground.
Even though we’ve had frost, there is still some harvest to be had among gardens and orchards. October is harvest time for animals as well as humans; many animals now are very active storing and hoarding food. From chickadees to voles to red squirrels to beaver, an animal’s success at finding and caching food will likely mean the difference between starvation and survival in the upcoming winter.
Storing up food is a full-time job. A pair of adult beavers typically stockpiles half a ton of tree branches to provide for their families through the winter. Red squirrels have been known to stash 15,000 cones along with hundreds of mushrooms in tree cavities and holes to tide them over.
Black bears also are quite active now, packing in the calories in preparation for upcoming hibernation. During the fall, bears are in a food frenzy—they eat constantly and may gain up to a third of their body weight in this season. In the fall, a hungry black bear might eat more than 20,000 calories per day. Compare that to the average human’s daily intake of 2,000-2,500 calories!
Throughout most of their range, black bears crawl into their winter dens between mid-October and mid-November. Individual bears choose denning times depending on food availability in the fall as well as their own physical condition. Female black bears, with or without cubs, tend to den up before males.
Become a phenologist! The cooler weather and occasional frost this time of year mean biting insects are not much of a bother—it’s an ideal time to hike or explore in the woods, and notice how plants and animals are preparing for the coming 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, September 28, 2007
Friday, September 21, 2007
Fall Colors
Nature Watch
September 21, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
What good is phenology? For some, it’s a year-round hobby that helps keep them in touch with the ebb and flow of the natural world. But the practice of noting and recording seasonal changes in nature does have what some would call more practical values.
For example, phenology is used to help with the prediction of insect emergence and strategies for insect control. Farmers, of course, are phenologists, and carefully correlate natural patterns and seasonal changes with crop planting and harvesting. Scientists who study global climate change trends pay close attention to the history of phenological data.
This time of year, the most obvious seasonal change is literally right in front of our eyes, as we are at the time of peak leaf color change among our deciduous trees.
The appearance of the beautiful yellows, reds, oranges we see is actually a result of the fading of the leafs’ green color, which is caused by cholorophyll. When chlorophyll fades, “beneath” it are other types of pigments that become revealed. These are the carotenoids, which produce yellow, orange, and brown colors; and the anthocyanins, which produce red, purple, and crimson colors.
The vibrancy of fall color is related to weather conditions that occur before and during the time when chlorophyll in the leaves is dwindling. A series of warm, sunny days and cool, crisp, but not freezing nights seems to bring about the most spectacular color displays.
Different tree species have characteristic color changes. Oak leaves usually turn red or brown. Aspens transform into golden yellow. Red maples turn brilliant scarlet and sugar maples change to an orange-red. Leaves of some species, such as the elm, just shrivel up and fall, while changing to a drab brown color.
The timing of the color change also varies by species. For example, oaks show their colors long after other species have already dropped their leaves. The differences in timing among species seems to be genetic, for a particular species at the same latitude will show the same coloration in high elevations at about the same time as it does in warmer lowlands.
Unique among the color-changing trees is the tamarack, also known as the eastern larch. In the spring and summer the tamarack has bright green flat, soft, and flexible needles. They are shaped uniquely on the branch in a whirled cluster somewhat like a flower’s petals. The trees are easy to identify by their narrow pyramid shape and their location—they’re most common in swampy areas.
This tree is both coniferous (produces cones) and deciduous (loses its leaves). Although the tamarack looks like an evergreen, it is not ever-green, because its needles change to a golden-yellow color in the fall and drop off.
On warm and sunny fall days, garter snakes can be found basking in the sun on rocks and fallen trees. Soon, they will find a rock pile or an abandoned ant hill where they’ll spend the winter in hibernation. This snake’s yellow stripes help camouflage it in the grasses of forests and open fields where it lives. The garter snake feeds on insects and small rodents like mice. It is not poisonous.
About this time, northern flying squirrels begin visiting oak trees to feed on acorns. As the acorns mature you might find partly chewed ones on the ground. The squirrels feed at night, so if you want to see them, look for the acorns then keep your eyes open for squirrels scrambling up the trees.
Become a phenologist! Take a fall hike and note all the different colors of the forest. Gather wild apples and make your own applesauce or cider. Soak up the fleeting warmth of sunny fall days as we turn our thoughts to colder weather.
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.
September 21, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
What good is phenology? For some, it’s a year-round hobby that helps keep them in touch with the ebb and flow of the natural world. But the practice of noting and recording seasonal changes in nature does have what some would call more practical values.
For example, phenology is used to help with the prediction of insect emergence and strategies for insect control. Farmers, of course, are phenologists, and carefully correlate natural patterns and seasonal changes with crop planting and harvesting. Scientists who study global climate change trends pay close attention to the history of phenological data.
This time of year, the most obvious seasonal change is literally right in front of our eyes, as we are at the time of peak leaf color change among our deciduous trees.
The appearance of the beautiful yellows, reds, oranges we see is actually a result of the fading of the leafs’ green color, which is caused by cholorophyll. When chlorophyll fades, “beneath” it are other types of pigments that become revealed. These are the carotenoids, which produce yellow, orange, and brown colors; and the anthocyanins, which produce red, purple, and crimson colors.
The vibrancy of fall color is related to weather conditions that occur before and during the time when chlorophyll in the leaves is dwindling. A series of warm, sunny days and cool, crisp, but not freezing nights seems to bring about the most spectacular color displays.
Different tree species have characteristic color changes. Oak leaves usually turn red or brown. Aspens transform into golden yellow. Red maples turn brilliant scarlet and sugar maples change to an orange-red. Leaves of some species, such as the elm, just shrivel up and fall, while changing to a drab brown color.
The timing of the color change also varies by species. For example, oaks show their colors long after other species have already dropped their leaves. The differences in timing among species seems to be genetic, for a particular species at the same latitude will show the same coloration in high elevations at about the same time as it does in warmer lowlands.
Unique among the color-changing trees is the tamarack, also known as the eastern larch. In the spring and summer the tamarack has bright green flat, soft, and flexible needles. They are shaped uniquely on the branch in a whirled cluster somewhat like a flower’s petals. The trees are easy to identify by their narrow pyramid shape and their location—they’re most common in swampy areas.
This tree is both coniferous (produces cones) and deciduous (loses its leaves). Although the tamarack looks like an evergreen, it is not ever-green, because its needles change to a golden-yellow color in the fall and drop off.
On warm and sunny fall days, garter snakes can be found basking in the sun on rocks and fallen trees. Soon, they will find a rock pile or an abandoned ant hill where they’ll spend the winter in hibernation. This snake’s yellow stripes help camouflage it in the grasses of forests and open fields where it lives. The garter snake feeds on insects and small rodents like mice. It is not poisonous.
About this time, northern flying squirrels begin visiting oak trees to feed on acorns. As the acorns mature you might find partly chewed ones on the ground. The squirrels feed at night, so if you want to see them, look for the acorns then keep your eyes open for squirrels scrambling up the trees.
Become a phenologist! Take a fall hike and note all the different colors of the forest. Gather wild apples and make your own applesauce or cider. Soak up the fleeting warmth of sunny fall days as we turn our thoughts to colder weather.
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, September 14, 2007
Migration
Nature Watch
September 14, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
We’re still in the thick of the season for bird migration. Though you may see many species “flocking up” as their departure time grows near, when do they actually take off?
The vast majority of birds migrate at night, so we usually don’t notice when they leave. For nighttime travelers like warblers, tanagers, vireos, orioles, kinglets, thrushes, many sparrows, catbirds, shorebirds, owls, herons, egrets, and waterfowl, study after study shows that migration is initiated 30 minutes to an hour after sunset.
Peak migration is usually from about 10 p.m. to midnight; the number of birds diminishes greatly four to six hours after sunset. Often in the hours before dawn, there are few to no birds aloft.
So why migrate at night? One hypothesis has to do with food and energy, and suggests that birds need to feed during the day before undertaking long flights. That makes sense since foraging at night for insects, seeds and berries would certainly be more difficult. However, some birds do forage and migrate at night, so there are exceptions.
The other explanation also has to do with energy. Nighttime migrants engage in powered flight—that is, they flap their wings rather than soar and glide in order to propel themselves. The nighttime atmosphere is cooler and less turbulent than during the day, so it’s easier and more energy efficient for birds to fly at night.
Powered migrants also generate enormous amounts of heat during flight; cooler night weather reduces loss of water that is used for stabilizing their body temperature. During long non-stop flights, the loss of water may in fact be more limiting than the loss of fat.
All that said, however, there are birds that migrate during the day. Some songbird species are true daytime migrants, like red-winged blackbirds, brown-headed cowbirds, grackles, finches, crows, and blue jays. Most of these species migrate much shorter distances than nocturnal migrants, so they tend to venture south with a series of short flights.
Soaring birds like hawks, pelicans, cranes, and swallows almost always migrate during the day. They depend on thermal updrafts to give them lift, and these warm funnels of wind are most available during the day.
Down in the forests and fields, one of our common wild neighbors is going through a traditional fall transformation. During the summer while his antlers grow, the male white tail deer socializes as part of a bachelor group. But as days shorten, his testosterone levels increase, his antlers harden and the velvet supplying blood to his antlers dries to a ragged sheath that falls off. He rubs off the remains, and from that time on he is a loner, focused on the mating season and using his keen senses to detect danger, rivals and receptive does.
The buck advertises his presence by leaving physical scrapes and signs. He applies scents from various parts of his body to broadcast his presence to other deer. Saliva, urine, and secretions from pre-orbital glands in front of his eyes, forehead glands at the base of his antlers, and tarsal glands on the insides of his hind legs all send aromatic messages to other deer.
Become a phenologist! Celebrate the autumnal equinox this September 23—that day when hours of day and night are equal and we officially enter the fall season. (“Equinox” means “equal night.”) Stay up a little later and bid farewell to departing migrant birds.
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.
September 14, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
We’re still in the thick of the season for bird migration. Though you may see many species “flocking up” as their departure time grows near, when do they actually take off?
The vast majority of birds migrate at night, so we usually don’t notice when they leave. For nighttime travelers like warblers, tanagers, vireos, orioles, kinglets, thrushes, many sparrows, catbirds, shorebirds, owls, herons, egrets, and waterfowl, study after study shows that migration is initiated 30 minutes to an hour after sunset.
Peak migration is usually from about 10 p.m. to midnight; the number of birds diminishes greatly four to six hours after sunset. Often in the hours before dawn, there are few to no birds aloft.
So why migrate at night? One hypothesis has to do with food and energy, and suggests that birds need to feed during the day before undertaking long flights. That makes sense since foraging at night for insects, seeds and berries would certainly be more difficult. However, some birds do forage and migrate at night, so there are exceptions.
The other explanation also has to do with energy. Nighttime migrants engage in powered flight—that is, they flap their wings rather than soar and glide in order to propel themselves. The nighttime atmosphere is cooler and less turbulent than during the day, so it’s easier and more energy efficient for birds to fly at night.
Powered migrants also generate enormous amounts of heat during flight; cooler night weather reduces loss of water that is used for stabilizing their body temperature. During long non-stop flights, the loss of water may in fact be more limiting than the loss of fat.
All that said, however, there are birds that migrate during the day. Some songbird species are true daytime migrants, like red-winged blackbirds, brown-headed cowbirds, grackles, finches, crows, and blue jays. Most of these species migrate much shorter distances than nocturnal migrants, so they tend to venture south with a series of short flights.
Soaring birds like hawks, pelicans, cranes, and swallows almost always migrate during the day. They depend on thermal updrafts to give them lift, and these warm funnels of wind are most available during the day.
Down in the forests and fields, one of our common wild neighbors is going through a traditional fall transformation. During the summer while his antlers grow, the male white tail deer socializes as part of a bachelor group. But as days shorten, his testosterone levels increase, his antlers harden and the velvet supplying blood to his antlers dries to a ragged sheath that falls off. He rubs off the remains, and from that time on he is a loner, focused on the mating season and using his keen senses to detect danger, rivals and receptive does.
The buck advertises his presence by leaving physical scrapes and signs. He applies scents from various parts of his body to broadcast his presence to other deer. Saliva, urine, and secretions from pre-orbital glands in front of his eyes, forehead glands at the base of his antlers, and tarsal glands on the insides of his hind legs all send aromatic messages to other deer.
Become a phenologist! Celebrate the autumnal equinox this September 23—that day when hours of day and night are equal and we officially enter the fall season. (“Equinox” means “equal night.”) Stay up a little later and bid farewell to departing migrant birds.
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, September 7, 2007
Summer's End
Nature Watch
September 7, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
It may still feel like summer, but the birds know better. Migration is peaking for many species, especially broad-wing hawks, and there’s no better place to witness this than up in Duluth at the Hawk Ridge Bird Observatory.
Broad-wings can be seen passing through, with the right winds, in enormous numbers. Like most raptors, they are reluctant to cross large bodies of water. When they migrate south and encounter Lake Superior, the birds naturally veer southwest along the lakeshore.
Broad-wings migrate at high altitudes and seldom stop to hunt during the days of their travels. Because of their dependence on cold-blooded terrestrial prey species, they migrate all the way to Central and even South America. In order to conserve energy on their long journey, they float upward on vertical air currents as high as they can go, and then shoot forward. These air currents, called thermals or updrafts, often are found above rock outcrops, buildings, or parking lots—surfaces that heat the air above them.
When one broad-wing discovers a thermal or updraft, others quickly join it, all swirling upward in a “kettle.” Their migration is one of the most exciting spectacles of the natural world. The Hawk Ridge Bird Observatory’s popular Hawk Weekend is scheduled for September 21-23 this year. In addition to broad-wing hawks, you may see various other raptors, the rarest of which include the peregrine falcon and gyrfalcon.
Use your sense of sound to pick up another sign of summer’s end. You’re probably familiar with that persistent hum in the trees on warm summer afternoons. That’s made by an insect called a cicada, using a pair of drumskin-like organs on the base of its abdomen. These vibrate at a high speed, making the buzzing noise, when the male cicada calls for a mate. However, that mating call drops off in mid-September, so the sound of fall—at least where the cicada is concerned—is actually the sound of silence.
The colorful Monarch butterflies we’ve seen all summer are beginning their migration south now. While most butterflies don’t stray too far from the area where they hatched, the Monarch is an exceptional exception. Every fall, in what is one of the greatest long-distance feats in the natural world, millions of Monarch butterflies embark on a trek that will take them hundreds, and in some cases, thousands of miles to wintering grounds in central Mexico.
North American monarchs are actually members of a group of tropical butterflies called Danaids. Like other tropical butterflies, Monarchs cannot withstand the freezing temperatures we get in this part of the world. But somehow, this creature has developed the capacity to avoid the cold winters by migrating south. Unlike many migrants, Monarchs make the trip without benefit of experience; they only live long enough to make the trip once.
A fall treat in the flower world is the New England aster, which you might find in roadside ditches or meadows, and is a glory to the eye in the fall landscape when most other flowers are gone. The New England aster comes in various shades of purple and can reach a height of four feet.
Become a phenologist! Mark your calendar each day you see a Monarch butterfly, then note the last entry this season. Seek out the last of the season’s wildflowers on your next walk or hike. Find a natural way to bid farewell to another fine summer.
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
September 7, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
It may still feel like summer, but the birds know better. Migration is peaking for many species, especially broad-wing hawks, and there’s no better place to witness this than up in Duluth at the Hawk Ridge Bird Observatory.
Broad-wings can be seen passing through, with the right winds, in enormous numbers. Like most raptors, they are reluctant to cross large bodies of water. When they migrate south and encounter Lake Superior, the birds naturally veer southwest along the lakeshore.
Broad-wings migrate at high altitudes and seldom stop to hunt during the days of their travels. Because of their dependence on cold-blooded terrestrial prey species, they migrate all the way to Central and even South America. In order to conserve energy on their long journey, they float upward on vertical air currents as high as they can go, and then shoot forward. These air currents, called thermals or updrafts, often are found above rock outcrops, buildings, or parking lots—surfaces that heat the air above them.
When one broad-wing discovers a thermal or updraft, others quickly join it, all swirling upward in a “kettle.” Their migration is one of the most exciting spectacles of the natural world. The Hawk Ridge Bird Observatory’s popular Hawk Weekend is scheduled for September 21-23 this year. In addition to broad-wing hawks, you may see various other raptors, the rarest of which include the peregrine falcon and gyrfalcon.
Use your sense of sound to pick up another sign of summer’s end. You’re probably familiar with that persistent hum in the trees on warm summer afternoons. That’s made by an insect called a cicada, using a pair of drumskin-like organs on the base of its abdomen. These vibrate at a high speed, making the buzzing noise, when the male cicada calls for a mate. However, that mating call drops off in mid-September, so the sound of fall—at least where the cicada is concerned—is actually the sound of silence.
The colorful Monarch butterflies we’ve seen all summer are beginning their migration south now. While most butterflies don’t stray too far from the area where they hatched, the Monarch is an exceptional exception. Every fall, in what is one of the greatest long-distance feats in the natural world, millions of Monarch butterflies embark on a trek that will take them hundreds, and in some cases, thousands of miles to wintering grounds in central Mexico.
North American monarchs are actually members of a group of tropical butterflies called Danaids. Like other tropical butterflies, Monarchs cannot withstand the freezing temperatures we get in this part of the world. But somehow, this creature has developed the capacity to avoid the cold winters by migrating south. Unlike many migrants, Monarchs make the trip without benefit of experience; they only live long enough to make the trip once.
A fall treat in the flower world is the New England aster, which you might find in roadside ditches or meadows, and is a glory to the eye in the fall landscape when most other flowers are gone. The New England aster comes in various shades of purple and can reach a height of four feet.
Become a phenologist! Mark your calendar each day you see a Monarch butterfly, then note the last entry this season. Seek out the last of the season’s wildflowers on your next walk or hike. Find a natural way to bid farewell to another fine summer.
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
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