Late Winter 2012
Winter is over (if it was ever really here). No more short days and Mid-Atlantic wacky weather. A Northern Hemisphere winter, generally defined as the coldest time of year, presents a unique set of challenges for living organisms. Reduced photoperiod, those shortened days of wan fleeting sunlight, is a stressor for all of us, plants and animals alike. Decreased temperatures and reduced access to available water round out the Big Three. All other problems of winter stem from these basic challenges: lack of food, need for shelter, increased predation threats. Tough times call for a tough crowd. Want to know what our wild neighbors were doing while we were inside waiting for spring? Winter and cold weather are vital to the life cycles of plants and animals. We could learn a thing or two about coping with stress from our friends in natural areas.
In This Issue
In Praise of Dormancy
Flora's Winter Dreams
Tracks in the Snow
Maryland's Rare Winter Birds
The easiest way to deal with winter is NOT to deal with winter. Leave. Fly south. Catch a warm current and migrate to Central or South America or the Caribbean and wait it out. Nice work if you can get it but what if your species can't move that far, or if you are a plant, what if your species can't move at all? Dormancy is one option.
Dormancy is defined as a period of inactivity when active growth and development temporarily stop. There are as many different ways to be dormant, each with its own vocabulary word, as there are groups of animals and plants. Of course, decreased temperatures are a problem for any creature that can't maintain its own body temperature at safe levels. These animals must find a way to survive when the mercury plunges.
What about our friends who can move around? Some animals manage to remain fully active during winter. Mammals use several strategies to get through the cold and dark. Mammals have fur, and unlike some synthetic fibers, natural fur does not freeze. Fur traps a layer of still air that retains body heat and keeps out the cold. (Some plants use this technique as well.) Active mammals will have fat stored up from greener times but must also search for food and water. That fox you see at Rocks State Park is warmer than you think. But being active in winter requires calories and the winter pantry is almost bare. The most successful active mammals are those that can take advantage of many food sources. Omnivores like opossums are experts at this, eating plants, small mammals, insects and grubs, garbage, human fast food, anything to get by. The raccoon, another omnivore, stays active but during times of extreme weather, it will hole up and wait it out, using up fat reserves. See more about active winter animals here.
To get around the energy use and dangers of being active in winter, some mammals will just "sleep" through it. Most of us know this as hibernation or torpor. An animal in true hibernation will drop its metabolic rate so low that is uses only a fraction of the energy needed to stay active. The reduced metabolic rate results in a lower body temperature, close to that of the surrounding air, near freezing. Breathing and heart rate slow to almost undetectable levels.
Prior to heading into their winter quarters, hibernators will spend summer and fall eating heartily. This creates a layer of fat to stave off starvation and to keep warm. Different from white adipose tissue, the fat these mammals produce before hibernation is brown fat. Brown fat lays over the shoulders, neck and upper back and actually generates heat; brown fat cells contain mitochondria, which are the power plants of the body. The brown color comes from iron in the mitochondria and the greater density of blood vessels woven throughout the fat. Newborn humans also possess brown fat to help keep them warm before their bodies learn to shiver.
There are different kinds of hibernation. True hibernators will not be roused easily; their metabolic rates remain depressed. Their bodies feel cold. Brain function almost ceases. Groundhogs, or woodchucks, are true hibernators. During hibernation, the groundhog's "ever-growing" teeth will stop growing. Chipmunks and some mouse species are true hibernators as well. True hibernators do not spend the entire winter in this state of near death, as was once previously thought. These animals will rouse every few weeks to leave their nest or den or burrow, stretch their muscles, re-boot their brains, maybe grab a snack of some stored food, urinate and defecate. Then they will go back into their deep sleep for another 2-3 weeks.
Bears go through a different kind of hibernation, what is more accurately called winter lethargy. A bear's metabolic rates don't decrease as much as those rates found in true hibernators, and its body temperature only drops by about 10-12 degrees. This variation is because bears give birth in January so the mother's metabolic rate must be high enough to carry out the activity of birth. (The energy needed to safely bring the rate up from true hibernation to one sufficient to support birth would expend too much energy to be safe and sustainable.) During birth, the mamma bear, or sow, will rouse enough to deliver and clean up the cubs. She will then go back to sleep while the cubs suckle, mostly unsupervised.
Bears don't usually leave their dens during winter. As part of their pre-hibernation prep, they increase their body weight by about 30%, focusing their diet on carbohydrates. A few days before entering their winter den, they will stop eating, clear their digestive tract then have a final meal heavy on fiber, pine needles, leaves, even their own hair. This fibrous material creates a fecal plug, called a tappen. Hibernating bears will not emerge to eat or drink for as many as 100 days and yet they do not become dehydrated. Their urine is concentrated into urea, with most of the water reabsorbed back into their bodies. The remaining solid waste is small enough to be stored in their colons. They don't need to urinate or defecate while in the den. They will live off their brown fat reserves for energy; their thick coats and fat insulating against heat loss. When they emerge from their dens in the spring, they will expel the tappen and get to eating. It may take them awhile to find food in the early spring so they often lose a great deal of weight at this time of year.
A bear in winter lethargy is a physiologic and metabolic wonder. In addition to maintaining a near perfect water balance, their cholesterol levels in winter are more than double the summer levels. Metabolism of brown fat will do this. And yet bears seem no worse for the wear: no gallstones, no hardening of the arteries. Bears do not experience calcium loss from bones or muscle cramping from lack of activity as happens in humans. Research is currently being conducted to find a way to translate this to human health, be it for nursing home residents confined to bed or astronauts in tight quarters in space.
Hibernation isn't just about cute fluffy animals curled up and snoring. Hibernation can leave an animal vulnerable to threats. In Maryland, most of our bats are hibernators, coming together in large groups to take up residence in caves, called hibernacula (singular: hibernaculum). Bats utilize brown fat, reduce their metabolic rates, and cluster to conserve energy. Because of their size, bats have a very small margin of error when it comes to awakening during winter. On average, a bat will lose a quarter to half its body weight during hibernation. They don't have a lot to spare. If they are roused during their winter sleep, they can burn just enough extra energy to leave them out of fuel before the end of winter. They starve to death before their insect meals emerge in spring. It is believed that this is one of the effects of White Nose Syndrome, a disease recently found in our bat populations. Colonies of bats found with WNS have been decimated by the fungus which causes them to rouse early from their winter's sleep.
And what about those insects the bats need? Their word for winter torpor is diapause. Diapause, or the developmental delay caused by adverse conditions, can occur in almost any of an insect's various life stages, depending on the species. Diapause may be a period of physical inactivity or a time of developmental delay. Bugs may overwinter as eggs (mantises), larvae (blowflies and beetles, many butterfly caterpillars), pupae or chrysalis (some swallowtail and hairstreak butterflies) and a few as adults (mourning cloak butterflies, crickets). Diapause can also occur during periods of great activity. The famous monarch butterfly will migrate while its adult phase is in diapause. These animals greatly reduce eating and reproduction until they have completed their journey. Insects in diapause can freeze too but their water-filled cells don't swell and rupture because they have natural antifreeze. In the fall, they begin to produce sugars, like glycerol and sorbital, in their hemolymph (insect blood). These sugars reduce the freezing point of hemolymph low enough so that the insect doesn't freeze to death.
Some insects, especially colonial ones like honey bees, ants and termites, will group together in their colonies and tough it out. Honey bees, which have tiny "hairs" all over their bodies, can generate heat by shivering; ants and termites will burrow into the soil below the freeze line and live in relative comfort off their stores.
The next time you go for a winter hike in Maryland's natural areas, remember all the critters snug in their bark beds and leaf dens and soil salons. They may not be out and about now but come springtime, they'll be rarin' to go.
Plants are the anchor of many food chains; any factor that affects plants will affect every other organism in that food chain. Mastering the nature of water has been the Plant Kingdom's ace in the hole when it comes to winter. Plants are essentially boxes of water, a collection of water-filled cells. When water freezes and expands, inflexible cell walls rupture, killing the plant.
Annuals, those plants that complete their entire life cycle in one year, avoid the problem altogether. Germinating from seeds, growing, flowering and producing seed, then dying – the challenge of winter is solved within the seed. Annual seeds have evolved to remain dormant through the winter and be ready to germinate as soon as spring conditions can support growth. In fact, seeds of overwintering plants NEED the cold to prepare the seed for germination when conditions allow. Without this cold period, some seeds will not sprout. This process is called vernalization. (Horticulturists will take advantage of vernalization to get their plants to germinate and flower out of season by putting the plants or seeds into "artificial winter", i.e. a cold room or freezer.)
Perennial plants, which come back year after year and may take multiple years to complete a life cycle, have a different set of strategies to make it through the winter months. They have developed ways to reduce water loss, conserve food resources, and not be destroyed by sub-freezing temperatures. Perennials can be divided into two types: deciduous and evergreen.
Leaves are a major source of water loss. Deciduous plants cope with winter by dropping their leaves when the days begin to shorten. This process is caused by the release of a plant hormone, abscissic acid. Loss of leaves results in no food production, no leaves to conduct photosynthesis. Conservation of energy is the order of the day as plants slow down their internal activity. At this time, food storage in root systems will maintain the reduced demands of the plant. Roots can be insulated by snow pack and those roots below the freeze line in soil will continue to take up moisture, where it is available.
In woody plants like trees and shrubs, when leaves fall, a plant must seal off the leaf site, creating scar tissue to prevent water loss. Herbaceous plants may die back all the way to the ground with only the root system remaining active. Some crafty herbaceous plants employ a strategy of basal leaves arranged in a ring or "rosette" pattern, which gets them a head start in the spring. In these plants, stems die back almost to the ground but rosette leaves will survive. Rosettes are close to the ground and often "hairy" underneath; both qualities reduce any air movement under the leaf, creating an insulation layer of still air. This design reduces water loss from the undersides of the leaves where leaves have pores that aid in respiration. The remaining rosette leaves can continue photosynthesis, at a much reduced rate, so the plant is ready to grow when the weather warms up. Some invasive plants, like garlic-mustard, use this strategy. This is one way they outcompete non-rosette-making native plants. Take a stroll on the tow path along the Potomac Gorge in the C&O Canal National Historical Park to see an example of this.
What about plants that don't drop their leaves – the evergreens? Needles are actually modified leaves. Needle-bearing trees - pines, spruces, firs and the like – along with evergreen hollies - will drop some of their needles each year but do not lose them all at once. This way, the plants get the benefit of using their leaves for more than one season and can photosynthesize during warmer periods in winter. These trees have developed additional strategies and structures for reducing water loss. Any leaf, needle or otherwise, must allow water and air to move in and out of the leaf as part of normal photosynthesis and respiration. Rates of these processes may slow during winter but they still occur. Air and water flow is regulated through pores in the needle's underside. In evergreens, these pores are smaller and more tightly closed than in broadleaf species like oaks or maples. Needles, like evergreen holly leaves, are also coated with a waxy substance called cutin that reduces water loss.
However, dark colored needles can also exacerbate water loss problems in
winter. Cooler cloudy days in winter are actually better for trees. On
warmer winter days, those dark needles absorb heat and raise the temperature
within the tree canopy above the surrounding air temperature. This increases
the tree's metabolic rate; water pressure inside the tree rises and is
relieved by water loss through the needle pores. You can see this phenomenon
on warm winter days in the mist around the conifers of Swallow Falls State
As you strike out on your early spring hikes this year, send out a quiet thanks to the plants and animals who made it through another winter. Those early shadbush and redbud flowers and spring peeper calls are the culmination of some tough winter work.
The winter season is a great time to explore the natural world around you. Snowfall is the perfect canvas and provides a great way to start learning how to track. The snow can capture the activities of animals and birds that share your area over time; even when you’re not there to witness their antics. Snow comes to your home and covers everything. It won’t be long until there are tracks to be followed and explored. Tracks in the snow make it convenient for a simple, fun, family activity. It is easier than you may think.
Some easy tracks to distinguish are opossums, bears and raccoons because their foot prints are unique. Others like those in the rabbit, rodent, weasel, feline and canine families are a bit trickier.
You will need a few skills in order to begin tracking. You must be able to count to five. Mammals in Maryland have either 4 or 5 toes on each foot, unless of course they have hooves. For example, you can quickly narrow animal groups by counting the toes on the foot prints. Rodents have 4 toes on the front feet and 5 toes on the rear feet (except beavers). Common rodents you might see include chipmunks, groundhogs (woodchucks), mice and squirrels.
Weasels have 5 toes on their front and rear feet. The Maryland weasel family includes long tailed weasels, minks, fishers and river otters. Cats and dogs show 4 toes on the front and 4 on the rear. So the first thing to do is count the toes.
You need to be able to determine left foot from right foot. Toes are always at the front of the footpads. Toes point you in the direction of travel. If you face the same direction you will know the right print from the left print. This will help you with the next skill. (See Raccoon photo above.)
The next step is to analyze the footfall sequence. It is another clue to help you distinguish front feet from rear feet and thus the number of toes on each. For example: if one print has been stepped on by the other, usually the one on top is the rear foot. In the cat photo you can see that the rear foot covers over part of the front foot and that the rear foot has 4 toes. (See Cat indirect register photo at right.)
If you have a set of four prints and one set is between the other two, the inside prints are the front feet. In the squirrel tracks you can see the 5 toes on the outside rear feet and the 4 toes on the inside front feet. (See Squirrel photo below.)
Be aware that most animal’s front feet are larger. Bears, rabbits and raccoons are notable exceptions. Your review of the foot fall pattern will help you better count up the number of toes on the front and rear feet and in turn help narrow down who you are following.
Size of the track itself will help you to further identify the owner. A larger track will indicate a larger animal. Taking pictures of the tracks and comparing them to online photographs is a great way to hone your skills. A good reference guide can help you recognize your neighbor. Tracking and the Art of Seeing by Paul Rezendes is an excellent reference book to have with you. If you are interested in bird tracks, Bird Tracks and Signs by Mark Elbroch is a very good tracking resource.
Tracking is not limited to your backyard or snowfall. You can track any time of the year. You want to find an area that has sand or mud and is near water. Maryland State Parks offer a wide variety of tracking opportunities. Susquehanna State Park located in Harford County has ample tracking prospects. It is home to deer, red fox, river otters, coyotes, squirrels, mice, chipmunks, raccoons, beavers, opossums, skunks, groundhogs, ducks, geese, herons, song birds, birds of prey and all types of amphibians and reptiles. Remember, anything that moves leaves a track! (Coyote photo)
Whether you and your family are tracking in your backyard or at the park, it takes a little practice to really get to know the differences between animals. Keeping photos, taking notes and keeping a reference guide nearby, can make tracking accessible no matter where you are. Though snow can be a help when you are learning, tracking is always in season. For more information, contact Margit Pruett of Rocks, Susquehanna and Palmer State Parks.
Twenty-five bird species are currently listed as Endangered, Threatened, or In need of conservation in Maryland. Some of these species, such as black skimmer, Swainson’s warbler, mourning warbler, and alder flycatcher, are only found in our natural areas as breeding birds. Others, however, have both breeding populations and overwintering populations. The American bittern, for example, is found in the winter as well as the summer, although this secretive marshbird is difficult to locate at any time of the year. In winter, short-eared owls hunt meadow voles in the extensive marshes of southern Dorchester County. Late afternoon along Elliott Island Road, in Fishing Bay Wildlife Management Area, often produces sightings of this mouser. The marsh just east of the bridge over the Transquaking River on Bestpitch Ferry Road is another good place to find this species.
The marshes of Fishing Bay and Blackwater National Wildlife Refuge are also your best hope for finding other rare wintering aerial predators. The meager numbers of northern harriers that breed in the higher, drier portions of these marshes are augmented in the winter by birds that have bred farther north. Rough-legged hawks breed in far northern Arctic tundra and taiga regions and head south for the winter. The Chesapeake Bay marshes are the southern limit of their wintering range in eastern North America. They also compete with northern harriers and short-eared owls, as well as other predators, for the abundant meadow voles living in these marshes.
One final raptor found regularly in southern Dorchester County in winter is the golden eagle. The wintering population of bald eagles around Blackwater National Wildlife Refuge is burgeoning; it is possible to find over a hundred individuals in a day there. However, searching the skies over Blackwater Refuge long enough in winter will often result in finding one of the small number of golden eagles that are, like their more abundant cousins, preying on injured waterfowl and scavenging on deer and other animals killed on the roads. Refuge biologists are trapping and attaching transmitters to golden eagles to help learn more about their winter movements and habitat needs. Golden eagles have also been tracked at Aberdeen Proving Grounds.
Maryland is the winter home for masses of waterfowl that breed farther north and northwest. Tundra swans wintering in Maryland breed as far as the north slope of Alaska. Although wintering Maryland populations of many waterfowl species have greatly declined as the health of the Chesapeake Bay declined, they are still common enough not to be considered rare winter residents. Gadwall, a rare breeding bird in Maryland, can be found in considerable numbers on some Maryland water bodies in the winter. Ruddy ducks and common mergansers are two other wintering waterfowl species that breed rarely in the state, although breeding common mergansers appear to be on the rise.
When birders think of rare winter birds, many think of the irruptive populations of winter finches, such as purple finches, pine siskins, redpolls, and crossbills. (An irruption is a dramatic and irregular expansion or migration of birds into an area they don't normally frequent.) Although some of these birds may show up regularly at feeders in the winter, their numbers statewide vary greatly from year to year. This is due to the cyclical nature of conifer seed production to the north, the birds' primary winter food source. While it is exciting to see these northern denizens, their winter populations are not as dependent on food supplies in Maryland’s natural areas as they are on food supplies in suburban backyard feeders throughout the mid-Atlantic and beyond. Several songbirds that breed only in parts of western Maryland are quite common statewide during winter. Yellow-rumped warblers fill the shrubs on the Eastern Shore, taking advantage of wax myrtle berries, and they flit among trees and shrubs across the rest of the state. Hermit thrushes, golden-crowned kinglets, and yellow-bellied sapsuckers also increase their range and their numbers in winter when northern breeders shift south to enjoy our Maryland hospitality. Extend a warm welcome to our winter visitors and residents by providing food, water, and shelter in your back yard, or enjoy these birds by visiting one of the many natural areas that support these species.
Not everyone has slept through winter. A few of our cold-blooded friends have something else in mind, like breeding. Yup, hard to believe but the urge to procreate and have young develop before seasonal ponds dry out has created a niche for certain species, like the State endangered Eastern Tiger Salamander. This large (up to 13 inches long) salamander spends much of the year underground. During the “mid-January thaw”, those warm rainy nights that always trick us into thinking spring is right around the corner, tiger salamanders congregate in vernal pools and Delmarva bays on the Eastern Shore. After some nuptials, the female lays a translucent mass of eggs attached to vegetation or downed tree limbs, often in the deepest part of the wetland. The eggs hatch in about 30 days, but the larvae or tadpoles can take up to another four months to develop, so in all it may take until May or June before the newly metamorphosed young clamber up onto land, not to return for 3-8 years. It's a race-against-time for the young to develop before those seasonal ponds dry out – part of the annual gamble that breeding amphibians take.
While the tiger salamanders are breeding, many reptiles are still hibernating. Reptiles use a type of hibernation call brumation to survive the winter chill. They hunker down in sheltered spots, under leaves or logs or they burrow into the soil. They become lethargic and stop eating although they continue to drink water when they can. For some reptiles, brumation is necessary for successful reproduction. Without that period of cold and lethargy, the egg will not properly form and will not produce young. Reptiles, with their thick scaly skin, lose water at a slower rate than amphibians, whose softer skin must remain moist.
Amphibians hibernate too but because their skin is moist, they must remain near a water source. Their metabolism doesn't slow down quite as much as a turtle's. Some aquatic frogs, like the American bullfrog, will hibernate underwater or at the edges of a pond; they can't stay down there indefinitely but must surface infrequently to breathe. Land-based frogs can burrow into the soil, below the frost line. Frogs that are not skilled diggers, like wood frogs, will find small sheltered spaces, like under rocks or logs, or they may snuggle into the leaf litter.
Even in their sheltered spots, the temperatures can dip below freezing. Ice crystals can form under a frog's skin or in its body cavity. So why don't they freeze to death? Antifreeze! The internal organs are protected because they contain a very high concentration of glucose, which prevents freezing. Even though the animals' hearts stop beating and they may stop breathing, once temperatures rise, the animals thaw out. If you hike in Idylwild Wildlife Management Area or Millington WMA this time of year, you may hear the early ruck-a-duck call of the wood frog or find a red-backed salamander under a rotted log or green frog and southern leopard frog tadpoles in the ponds.
Our natural areas provide us with so many things that improve our quality of life: open spaces for contemplation and recreational opportunities, clean air and water, habitat for plants and animals that enrich our world. Over the last 25 years we have become more aware of the benefits to physical and mental health that come with contact with the natural world.
Funding for "nature" as a public resource comes from many sources, both public and private. Some funding sources are specific to an activity, like funding from taxes on hunting or fishing gear. Some may fund only animal-related issues. For non-game and endangered species conservation work and for work on plants, there is one important source in the State of Maryland that comes from you, the conservation-minded tax payer. It's called the Chesapeake Bay and Endangered Species Fund. Around here, we call it the Tax Check-off.
The Tax Check-off (line 35 on Form 502 or line 13 on Form 503 of your MD state tax return) is a voluntary donation you can choose to make through your state tax return. Money from the Chesapeake Bay and Endangered Species Fund is shared between the non-profit Chesapeake Bay Trust and the MD Department of Natural Resources and is put toward a variety of projects, including grants for education, rare species conservation and ecosystem restoration. And your donation is tax deductible the following year!
Nature is free. Our knowledge of it and our ability to conserve it for our children's children is not. The Tax Check-off is one way you can say where your money goes.
Saturday, April 21, 2012: 9th Annual EcoFest
Celebrate Earth Day with this free festival at Druid Hill Park. Learn about sustainable living in an urban environment. There will be demonstrations, activities for children and adults, food and vendors. Stop by the MD Wildlife & Heritage table and learn about educational opportunities for elementary and secondary grades. Noon to 5pm. http://baltimoregreenworks.com/events/ecofestival/
April 26 – 29, 2012: Delmarva Birding Weekend
Visit the natural areas of Maryland's Eastern Shore and Delaware and meet its feathered denizens. Bird by foot, car and boat. Catch the spring migration in all its glory! Click here for more information. http://delmarva-almanac.com/index.php/contrib/birdingweekenddates
October 9-12, 2012: Natural Areas Conference 2012
SAVE THE DATE! Keeping Natural Areas Relevant and Resilient. Learn about the latest research in species, habitat and management and conservation of natural areas. Meet others working in this area and share strategies. Register early. Norfolk, VA. http://www.naturalarea.org/
MD Natural Heritage Program
Green Treefrog: Kerry Wixted
Seaside Dragonlet: Kerry Wixted
Scarlet Tanager: George Jett
American Lotus: Kerry Wixted
Snowshoe Hare: MD DNR, 2005
Black Bear sow and her cubs: MD DNR
Eastern Tiger Swallowtail butterfly: John White
Hunting Creek Lake: R.H. Wiegand
Garlic-mustard: K. Wixted
Hemlocks at Swallow Falls State Park: K. Wixted
All photos of tracks: M. Pruett
American Bittern: M. Wilson, USGS
Tundra Swans: M. Hendricks.
Eastern Tiger Salamander: Jim White
Eastern Red-backed Salamanders: John White
Cerulean Warbler: D. Bales
Martin Mt. Sandstone Glade, R.H. Wiegand
Piney Reservoir, Garrett County, MD: David Kazyak
Sunrise on Assateague: R.H. Wiegand
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