The changing natural world at our doorsteps | By Patterson Clark
September 27, 2011
Cooper's hawks on the rise
During the summer, Cooper's hawks spend much of their time in heavily wooded areas, waiting for a chance to swoop through the foliage and seize a dove, robin or chipmunk.
But now they have begun to migrate, and the solitary, crow-size hawks are easier to see, especially in the mornings, sailing south.
They may reach the Florida Keys, where they tend to congregate before perhaps flying on to Cuba or the Yucatan for the winter.
Cooper's hawks are in the Washington area year-round, but winter's birds come here from farther north.
A century ago, Cooper's hawks were condemned as chicken killers and shot on sight. But a combination of conservation efforts and a steady increase in older forest cover has boosted the population.
By taking feather samples from a migrating first-year Cooper's hawk, a scientist can determine the latitude where the bird was raised. The feathers contain small amounts of the hydrogen isotope deuterium, which occurs in concentrations distinctive for certain latitudes.
Feathers from older birds are a less-reliable gauge of latitude, perhaps because older birds often grow new feathers as they migrate, and the reserves they use to build new feathers may have come from prey caught at various latitudes.
SOURCES: Thure Edward Cerling, University of Utah; U.S. Geological Survey Patuxent Wildlife Research Center; Audubon.org; The Condor; Science; University of Michigan
October 4, 2011
Black walnuts: Worth the trouble
Fortunate is the alley pelted in early October with the fat fruits of native black walnut trees. Tires from passing vehicles can crush the gooey green husks, leaving behind the rock-hard nuts for harvest.
Black walnuts are encased in a thick, woody hull, a challenge to remove but well worth the effort. Nutmeats yield an oily, woodsy flavor, much stronger and richer than that of ordinary English walnuts.
Tips for walnut harvesters
If car tires haven't husked the nut for you, follow these steps:
Wear gloves to avoid staining hands with husk pigments.
Select fruits with soft green husks. Avoid gathering fruits with black husks, as heat from the decaying husk will discolor the nutmeat and ruin its flavor.
Wearing rubber boots, stomp off the green husk to expose the nut.
Thoroughly wash nuts in water. Pour the waste water down the drain. Husks contain juglone, toxic to worms and many plants.
Nuts that float or have hairline fractures may not be good, so set them aside to use as a last resort.
Air-dry the washed nuts indoors on a screen for several days before storing in a cool spot for three to six weeks. Nuts that rattle slightly when shaken are cured and ready to crack.
Slowly crack a cured nut between the jaws of a vise. Or wrap a cured nut tightly in a tough rag, place on a butcher block or concrete floor and whack with a heavy hammer.
The hull will shatter into several sharp pieces, from which chunks of nutmeat can be picked.
Nutmeats can be frozen for up to two years or kept fresh in an airtight container in the fridge for nine months.
Sources: Center for Agroforestry, University of Missouri; University of Minnesota Extension; U.S. Forest Service; tomclothier.hort.net.
October 11, 2011
Foliage map: Autumn's showy march to the sea
Although our nights are getting longer, Washington's trees are still mostly green. People who want to see fall color must drive north or into the mountains. The cooler temperatures there have triggered deciduous trees to stop replacing chlorophyll in their leaves. When the chlorophyll breaks down, weaker yellow pigments become visible. Red pigments are produced in some tree leaves, setting visual fire to the forest.
Peak dates for fall color are determined by a combination of latitude, elevation, the cooling effects of rainfall and proximity to the ocean.
October 18, 2011
Red maple leaves on the C&O Canal.
October 25, 2011
Stinkhorns: Rank mushrooms from the mulch
A wet autumn provokes the emergence of mushrooms, the most visually startling of which are the stinkhorn fungi.
Phallus rubicundus commonly occurs in sun-drenched wood-chip mulch, where its mature fungal threads produce an egg-shaped structure at ground level. In the early morning an orange stalk rises from the "egg." The spongy fruiting body lasts for only a few hours, usually collapsing by noon.
The stalk's cap exudes a brown, spore-laden slime that discharges a fetid odor, which attracts flies.
The slime sticks to the feet of the insects, which spread the fungus when they land on damp mulch. But a more effective form of spore dispersal begins when the flies feverishly sponge up the sticky, stinky syrup, consuming as much as 80 percent of their body weight in stinkhorn slime in a single day. The putrid breakfast doesn't sit well with a fly's digestive system. When a bout of diarrhea ensues, intact stinkhorn spores make their exit. Each resulting fly speck can contain more than 22 million stinkhorn spores.
P. rubicundus may employ hapless flies to spread itself locally, but the fungus has found an even more effective vector in human commerce. The transport and sale of wood chips has rapidly expanded the stinkhorn's range from the southern United States into the Northeast and upper Midwest.
The mushroom is not edible.
SOURCES: Mushroomexpert.com, Journal of Mycology, University of Hawaii Press
November 1, 2011
DeKay's brown snake: A discreet reptile makes a conspicuous journey
In eastern U.S. cities and rural lowlands, a common but shy snake is on the move.
DeKay's brown snakes spent spring, summer and early fall hiding under rocks, logs and leaves, feasting on earthworms and slugs, while avoiding the jays, cats and shrews that would make a meal out of the 6- to 13-inch reptiles.
But in late October and early November, the little
snakes expose themselves as they abandon their hiding places and slither across gardens and paths in search of hibernation holes, or hibernacula, which they often share with other small snake species.
A common option for a hibernaculum is an ant nest.
Without any larvae or pupae to defend in the late fall, ants are much less likely to attack snakes
entering their burrows. After the ants have retreated to the deeper recesses of the nest, snakes slither down the tunnels to hibernate just above their hosts, but still below the frost line.
Sources: Transactions of the Kansas Academy of Sciences; Savannah River Ecology Laboratory, University of Georgia; University of Michigan Museum of Zoology.
November 8, 2011
Osage orange: Rebound from the brink
In November, softball-size fruits of the Osage orange tree collect on the ground, waiting for large mammals to stroll by and consume them.
Giant sloths, mastodons and ancient relatives of the horse may once have fed on the sticky, bright-green globes but once humans reached North America and wiped out those megafauna, nobody was left to disseminate the seeds.
The tree's broad range eventually shrank to a small area straddling Texas, Arkansas and Oklahoma, where Osage Indians made and traded bows from the tree's highly prized, super-hard wood.
The tree began to spread again when European colonists planted it to contain their livestock. When cut, Osage orange stumps produce vigorous, thorny sprouts that form an impenetrable hedge that is "horse high, bull strong and pig tight."*
These hedges faded after the invention of barbed wire in 1875, but the tree continued to spread in a new role as a drought-tolerant, pest-free shade tree for urban areas.
City dwellers may observe squirrels or birds picking out the seeds from Osage orange fruits, but those animals destroy the seeds in the process. Only one beast will eat the whole fruit and successfully disperse the seeds in its manure. It's a large mammal introduced to this hemisphere by Europeans: the horse.
*Jonathan Turner, 1847
SOURCES: Arnold Arboretum, Harvard University; U.S. Forest Service
November 15, 2011
For dark-eyed juncos, it's "ladies first"
As days grow shorter and colder, dark-eyed juncos appear. Some will remain in the Washington area until after the cherry trees bloom.
Also known as snowbirds, the cold-loving sparrows are arriving from breeding grounds north of here. The species also breeds in the higher elevations of the Blue Ridge and in the mountains of West Virginia.
While Yankee juncos migrate south, mountain populations often simply fly downhill for the winter, where the climate is milder.
Leaving hubby with the kids, adult females tend to depart about two weeks earlier than males and juveniles, forming flocks that can be 80 percent female. Their head start results in winter populations that generally have a majority of females in southern flocks, and chiefly male flocks farther north and higher on the mountainsides.
Determining junco demographics at your bird feeder can be challenging: males and females look very similar. Juncos exhibit a wide range of variation in plumage, but males tend to have darker gray heads, while females sport more brown on their backs and wings.
SOURCES: The Condor, the Auk, USGS Breeding Bird Atlas, McGill Bird Observatory, www.ebird.org
November 22, 2011
Wrestling with winter's weeds
By the time the first frost seizes the garden, winter's weeds have germinated and are growing profusely. Some, such as chickweed, are already in bloom.
Resembling big, green snowflakes, rosettes of hairy bittercress, another plant that thrives in cold weather, proliferate on exposed garden soil. Some sprouted weeks ago after slender pods atop their mother plant exploded, propelling seeds as far as 16 feet.
Bittercress survives hard freezes, making it available throughout the winter for those of us who enjoy it as a peppery addition to salads. The leaves are smaller than watercress, a milder-tasting, more succulent relative.
Vegetable gardeners who prefer to curb winter weeds rather than eat them can thwart weed sprouts by applying a thick layer of tree leaves to the soil, robbing the weeds of sunlight.
When spring arrives, the tree leaves can be raked away from vegetable beds before planting, then used throughout the summer as a handy mulch. By this time next year, the leaves will have decayed, enriching the soil.
Most hardwood leaves work well as a mulch, but gardeners should avoid using the leaves of either the black walnut or the tree of heaven, which contain compounds that can suppress the growth of vegetables.
SOURCES: Virginia Tech, www.gardenorganic.org.uk, Plants For A Future
November 29, 2011
Shutting down for the season
The caterpillars can be completely black, but most often they are ringed by a coppery band, the width of which is highly variable, even among siblings. The band tends to increase in width as a caterpillar matures. Contrary to folklore, the width of the band has nothing to do with how cold the winter will be.
Cool weather prompts the caterpillars, which hatched earlier in the autumn, to wander around in search of a spot to spend the winter in dormancy.
Curling up under a few leaves won't prevent freezing temperatures from reaching the caterpillar, but the insect is equipped to handle it. A woolly bear has an antifreeze in its hemolymph, or circulatory fluid, so even after being frozen in solid ice, a caterpillar can thaw out and return to activity in the spring.
Then, after a few weeks of feeding, woolly bears will finally spin a cocoon and pupate, emerging a month later as black-specked, tan moths, which will lay eggs on a wide variety of trees, shrubs and herbaceous plants, including, clover, nettles, dandelions, maples and elms.
SOURCES: Encyclopedia of Life, National Phenology Network, American Midland Naturalist
December 6, 2011
The sycamore: Tall, pale and thin-skinned
After the leaves have dropped, the ghostly white trunks and limbs of the American sycamore visually leap out from the somber timber around them.
Sycamore bark is smooth and pale because the trees exfoliate their bark in the summer. As branches thicken, their brittle, tan outer bark splits into pieces that curl up and flake off, revealing a gray, white or greenish smooth inner bark. Several theories suggest how sycamores might benefit from bark shedding:
Shucking old bark could help jettison pests clinging to the bark.
A thin bark might allow the fast-growing tree to release water more efficiently during transpiration, which would accelerate growth. The tree's smooth inner bark can turn green with chlorophyll and continue to manufacture carbohydrates in the autumn and early spring while the tree is leafless.
Roots absorb oxygen necessary for respiration in the tree's cells, but sycamores often grow near waterways, where water-saturated, oxygen-poor soils are common. Compared with thicker bark, a thin bark might be better able to absorb oxygen and help counter the roots' absorption deficit.
Sycamores thrive in urban settings, where their rapid growth, wind resistance and tolerance of pollution and compacted soils make them good street trees. American sycamores, however, are vulnerable to anthracnose infections, so urban arborists tend to favor planting disease-resistant American-Eurasian sycamore hybrids, such as the London planetree.
SOURCES: New York City Dept. of Parks and Recreation, U.S. Forest Service, Ohio State University, American Midland Naturalist, Casey Trees, Colorado State University
December 13, 2011
The house mouse: A creature is stirring, like it or not
House mice venture beyond the walls to populate the outdoors in warm months. But unlike native mice, the
house mouse struggles to survive a winter outside and must seek warmth and food indoors. Mice can occupy a home undetected for a while, but sooner or later their human hosts will find mouse spoor. Rod-shaped droppings, chewed-open food packages, a glimpse of a mouse running for cover or the late-night sound of a rodent gnawing on a wall can motivate an effort to de-mouse the house. And for good reason:
Some studies indicate that 40 percent of human breast cancer tumors contain viral DNA that is strikingly similar to that of the mouse mammary tumor virus. Researchers continue to investigate what this might mean.The Institute of Medicine does not list mice as an environmental concern for breast cancer.
Excluding mice from the home is a healthful ambition, but before attemping to trap or relocate mice, people should seal possible entry points into their homes. Any hole or crack as wide as a fingernail will be an open invitation for a chilly mouse. (Tip: Avoid using spray-foam insulation mice will chew right through it. Instead, plug holes with steel wool or bronze mesh.)
SOURCES: Centers for Disease Control and Prevention, British Journal of Cancer, Cancer Research, Cancers, Internet Center for Wildlife Damage Management, University of Michigan Department of Zoology, Humane Society of the United States
December 20, 2011
American Holly: Go ahead and take a bough if you must
When the Pilgrims began exploring Plymouth's beaches in December 1620, they were heartened, so the legend goes, to find American holly trees growing near the shore.
The religious refugees might have found spiritual comfort in the sight of the tree, which is related to and closely resembles European holly, a traditional symbol of Christmas.
Even before Christianity, followers of Europe's indigenous traditions decorated with holly during midwinter festivals. For some, the evergreen foliage and persistent red berries symbolized fertility and the promise of spring.
In the United States, holly's seasonal popularity led
to widespread decimation of the slow-growing tree during the first half of the 20th century, prompting some states, such as Maryland, to ban the sale of boughs of holly.
The tree has gradually recovered (perhaps helped in part by consumers focused on buying synthetic decorations), and the law is no longer in effect: "It is not illegal to sell fresh holly boughs," says Vanessa Orlando, the state's Department of Agriculture spokeswoman, "So, deck the halls!"
Holly branches should be cut cleanly from the tree with a saw or pruners. (If the tree's not on your property, be sure to ask permission first.) Breaking off a branch will render the tree much more
vulnerable to deadly diseases.
To help preserve the decoration, apply a layer of shellac to the boughs before using them for trimming. When the season is over, store the boughs with your other ornaments; they will last for years.
Or, consider not cutting a bough, leaving it intact on the tree a gift to the birds and mammals that are also attracted to the deep-red berries, which help sustain wildlife during the winter.