The changing natural world at our doorsteps | Illustration and text by Patterson Clark
January 3, 2012
American crows: Rebounding from a lethal epidemic
American crows have tight-knit families during the breeding season, with adult daughters and sons helping their parents raise the yearly brood. Even after young adults finally leave home to start their own families, they will occasionally fly over to visit the folks or sail off to catch up with a sibling. But close kinship breaks down when a crow family joins a large winter flock.
Similar to a human clan arriving at a mall for a post-holiday sale, once crow parents and offspring enter a flock, they split up and do their own thing. "They arrive together, but they don't stick together," says Kevin J. McGowan, an ornithologist at Cornell University. Crows resume family ties when the flock disbands in the spring.
Winter flocks may find advantages to living in cities, where they are safe from hunters and they find food in landfills and mall dumpsters. But crows do like making trips to the countryside. "They are always on the lookout for waste grain in agricultural fields," says McGowan, "and they will eat any animal they can subdue." Their meat menu for the winter includes mice, road kill and overwintering corn-borer caterpillars that crows peck out of the bases of cut corn stalks. Crows will also visit bird feeders, says McGowan, "but they are nervous about that."
Some of the flock's older birds are survivors of an epidemic that wiped out almost half of the local crow population in 2004, when West Nile virus arrived in the area. The virus, spread by certain mosquitoes, has mutated to become especially lethal to crows, killing every crow it infects.*
But after the epidemic, crow numbers stabilized and even seem to be recovering. Scientists don't see much evidence that crows have built an
immunity against the virus, says McGowan, suggesting that conditions may need to be just right before another epidemic occurs. "There's always a potential for a flareup," he says, "but we don't have the slightest idea what could trigger it."
* In contrast, most human infections go unnoticed, and mortality is much less than 1 percent.
SOURCES: Centers for Disease Control and Prevention, Audubon, Penn State University, USGS Patuxent Wildlife Research Center
January 10, 2012
Poking up through almost every winter yard are bright green tufts of wild onions.
Several species from the edible genus Allium, including wild chives, nodding onion, wild garlic and meadow garlic, look very similar this time of year, with wispy, hollow, tubular leaves growing from underground bulbs. In the winter, while the leaves are still tender, people sometimes dig up the strong-tasting green clumps for culinary use, finely chopping the leaves for salads or dicing and stir-frying the bulbs.
When collecting any wild plant for the dinner table, avoiding dangerous look-alikes should be the first priority. Some poisonous lilies resemble wild onions, but none of them smell like onions when their leaves are crushed. If it smells like an onion, it is an onion.
Any sort of onion or garlic is toxic to dogs and cats, but Allium is beneficial for people to eat. Onions and garlic are antimicrobial and help reduce blood pressure and cholesterol. Several studies support the claim that garlic can help cleanse the body of heavy metals, but the plants also absorb heavy metals from whatever they're growing in so eating any Allium harvested from roadsides or industrial sites is probably a bad idea.
SOURCES: National Institutes of Health, Food and Chemical Toxicology, Environmental Protection Agency, Journal of Venomous Animals and Toxins including Tropical Diseases, Indian Journal of Nephrology, International Journal of Environmental Research and Public Health
January 17, 2012
Sweet autumn virginsbower
A potent remedy in dainty clothing
A potent remedy in dainty clothing
As a stiff winter gust rakes through a frostbitten heap of sweet autumn virginsbower, a plumed seed surrenders its grip to swirl down the alley, where an eddy gathers it with others into a rolling pile of fuzz. If the seed ultimately finds its way onto cool, moist soil, it may germinate in late spring to sprout a sprawling invasive vine, notorious for swarming over forest edges and creek banks.
In 1864, Clematis terniflora was introduced to the United States from East Asia as an ornamental plant. In late summer and autumn, the perennial climber adorns itself with fragrant, snow-white, cross-shaped flowers.
Perfume, prettiness and a precious name can mask the fact that C. terniflora synthesizes some potent compounds. Like other members of the buttercup family of plants, sweet autumn virginsbower is considered to be at least mildly toxic unless the plant is dried or cooked.
Traditional Chinese medicine, however, attempts to harness the chemical power of C. terniflora by using dried pieces of the root to treat cataracts and a variety of inflammatory ailments, including arthritis, prostatitis, hepatitis, mastitis, bronchitis and gout.
The Japanese use a name for the vine that may be more appropriate to its formidable nature. Sennin-so is a name inspired by the seed plumes, which are reminiscent of a hermit's beard. Translation: Wizard plant.
SOURCES: YanQiu He, Global Invasive Species Database, Journal of Ethnopharmacology, Encyclopedia of Traditional Chinese Medicines, Flora of China, Chemistry of Natural Compounds, Plants for a Future, Japanese Treasure Tales, uncultivated.info
January 24, 2012
Mourning doves: Gluttons of the bird feeder
Few birds can clean out a bird feeder faster than a mourning dove, which can eat as much as 20 percent of its body weight* in food per day.
To do this, doves need easy access to the chow. A feeder with a perch, a platform feeder or birdfeed simply strewn onto the ground will do the trick. Flat, bare ground works best. Doves don't scratch for food, so they need to be able to walk around and gorge on visible morsels.
Mourning doves eat seeds: grass seeds, weed seeds, flower seeds, pine nuts and their favorite, corn and other grains, which they will eagerly stuff into their crop.
The crop is a digestive storage organ that slowly releases food into the gizzard, where seeds are ground into an easily digestible mash. To aid the grinding, the birds consume small stones and even tiny glass fragments that collect in the gizzard.
In winter, the walls of a dove's crop are thin and translucent, but when breeding begins in the spring, the crop's inner layers thicken, slough off and break down to form crop milk, which both parents regurgitate into the mouths of their chicks, or squabs.
Formation of crop milk begins to subside a few days after the squabs hatch, giving them a bit of time to adjust to a diet of raw seeds. The parents supply those seeds for almost a month, until the squab has learned to feed independently. One percent of a dove's diet includes animal parts, usually snails, which parents eat during the nesting season, probably to provide an extra nutritional boost for their hungry squabs.
* The average dove weighs 121 grams a quarter-pounder.
Source: Ecology and Management of the Mourning Dove
January 31, 2012
An abundant remedy for the flu? Never mind.
An abundant remedy for the flu? Never mind.
By late January, when most trees have been stripped of their holiday decorations, sweetgum trees are still hanging on to many of their own spiky ornaments. The tree's russet, prickly fruits, or "gumballs," resemble a cluster of twisted, gaping bird beaks or a three-dimensional version of the biohazard symbol. They are so distinctive and durable that some people gather them in December to craft into holiday decorations.
In late autumn, before the gumballs surrender to glue guns and glitter, they complete their natural duties by opening their beaks and releasing a few winged seeds Those aborted seeds raised eyebrows in 2008, when chemist Thomas Poon and his team of student researchers revealed that sweetgum's aborted seeds are rich in shikimic acid, a hard-to-find compound used to synthesize Tamiflu, a drug that helps curtail and prevent influenza infections. Before the discovery, the primary source for shikimic acid was star anise, where it is found in limited concentrations.
Nevertheless, sweetgum missed its opportunity to become a modern pharmaceutical plant. "A much better process for producing shikimic acid was developed shortly after our discovery," says Poon. "The new process uses genetically modified bacteria, which can be efficiently grown in labs to produce the shikimic acid."
Bacteria, however, make for a lousy wreath.
SOURCES: Claremont McKenna, Pitzer and Scripps colleges; Tetrahedron Letters; U.S. Forest Service
February 7, 2012
The primeval world of moss
Cool, moist months are green season for moss. That's when it catches an extended break from summer's heat, which can desiccate the plant, shriveling it into dormancy.
A velvet ribbon of moss can thrive in the protective recesses of the narrowest, most heavily trafficked crack in a sidewalk. Moss sets up shop when airborne spores settle in the crack and are activated by moisture. Initial algaelike filaments mature into male and female plants with tiny leaves only one cell thick.
Moss will accumulate windblown dust, building soil beneath it. If untrampled, a moss mound will rise and spread beyond the crack, generating an oasis that can sprout seeds of flowering plants.
Mature male moss releases weak sperm, which will fertilize eggs held by mature female plants if the sperm can swim to them. Without a watery path to the egg, the sperm stands little chance of accomplishing its mission unless the right bug arrives.
In 2006, ecologist Nils Cronberg and colleagues demonstrated that moss can be fertilized by small arthropods (springtails and mites). These tiny, winter-hardy critters are drawn to fertile moss, which produces nutritious sucrose, starches, fatty acids and mucilage. That plant/animal relationship may stretch back almost half a billion years, during the early stages of life colonizing land.
But now, down in that sidewalk crack, moss fertilization has produced zygotes, which have developed into spore-producing stalks growing out of the tops of mother plants. To a fast-paced pedestrian, these sporophytes might look like whiskers poking out of a fuzzy green fissure in the pavement.
Sources: Science; Jon Shaw, Duke University; Ohio Moss and Lichen Association; University of Missouri Extension
February 14, 2012
Fruit flies: Love among the peelings
If you seek a little companionship, stay home and peel a ripe banana. You may soon get a visitor, or several: curious fruit flies, which seem to find their way into every home and office.
If the little flies are fortunate, the odors they're tracking will originate from the sloppy sweet rot of fermenting fruits prime spots to propagate.
For a fly to crank up its life cycle, it must first find a fly of the opposite sex. The spark starts when an ardent male approaches a female and taps her with his foreleg. An organ on his leg can taste whether she's fertile and the right species. If so, the pursuit begins.
As a male chases the larger female, he extends a wing and vibrates it, playing his courtship song. He eventually gets close enough to lick her posterior and will attempt to mate.
But it's the female that makes the decisive move. If she finds the guy fly suitable, she'll spread her wings and allow him to mount, where he'll remain for as long as 20 minutes. Usually less.
The next day, a fertilized female can begin laying hundreds of eggs, preferring to deposit them onto that drooling peach you left out. Within a day or two, eggs hatch into tiny maggots that feast and molt for about four days before they wriggle off to find a dry spot to undergo metamorphosis. After four or five days, adults emerge, charged up and ready to mate in less than a day.
Scientists are keen on fruit flies as laboratory animals. The flies breed efficiently at room temperature, they have a rapid life cycle and they present visually distinctive sex differences and broad genetic variations. The insect is one of the most intensely studied organisms, the subject of more than a hundred years of genetic research.
Fruit flies may be welcome in the lab, but in the home they are pesky. People who let fruit decay in the wastebasket and then become annoyed by their swarm of new fly friends can end the fun with a vinegar trap, a small container of apple cider vinegar laced with a few drops of liquid soap. The soap breaks the vinegar's surface tension, allowing enticed flies to flounder and drown.
February 21, 2012
A.k.a night partridge, timberdoodle, bog sucker
A.k.a night partridge, timberdoodle, bog sucker
Exploding into flight with stout, whistling wings, a chunky, robin-size bird leaves behind a bare patch where it was roosting on the ground during a light snowfall.
Flushing an American woodcock can be a startling experience. The half-pound birds are well-camouflaged and rest motionless on the ground until potential danger is only a step away. The bird's large, set-back eyes scan a 360-degree view so they aren't the ones being surprised.
From the sandpiper family, woodcocks have adapted to brushy woodland environments, including urban thickets. Instead of probing sand or mud flats for food, these solitary woodland sandpipers plunge their three-inch bills into loose, damp soil in search of invertebrates, mainly earthworms. The bird can flex its upper bill near the tip, allowing it to nab prey from the loamy depths.
Although some woodcocks spend winter in the Washington area, more arrive from points south in February, when males begin their courtship displays at dawn and dusk.
Standing in a clearing, a male calls out a buzzy peeent! He shifts position and peeents again. After a few calls, he takes to the air, ascending in wider and wider circles until he's hundreds of feet up, at which point he begins chirping and flutters back down to the same spot or next to a fascinated female and replays the display.
After mating, a female is on her own. In a slight depression on the floor of a thicket, she lays about four eggs, which normally hatch in late March. A few hours after hatching, chicks follow their mom through the brush, becoming independent before May.
Woodcocks are in decline. Their North American population has fallen by about 1 percent every year since 1968, probably because of a loss of habitat: fewer old fields sprouting dense, young forests.
But one agricultural transformation may help the bird. More farmers are employing no-till planting methods in their fields, a practice that vastly increases earthworms in cultivated soils, where woodcocks are known to feed, usually before sunrise and after sunset.
SOURCES: University of Michigan Museum of Zoology, www.ebird.org, Wildlife Management Institute, U.S. Fish and Wildlife Service, Life Histories of Familiar North American Birds, Megadrilogica
March 6, 2012
Red Maple: Chancing an early spring
Warming temperatures have sprung open the flower buds of red maple, one of the first trees to bloom as winter fades. Each bud unfolds about half a dozen tiny, dark-red blossoms, each shaped like a wee tulip. Although most red maples bear either exclusively male or female flowers, some trees produce both, the proportion of which can be highly variable from year to year.
Red maples yield a sap as sweet and flavorful as that of a sugar maple. However, the window for making red maple syrup has passed: Once the tree "breaks bud," the sap's chemistry changes, imparting an unpleasant taste to the syrup.
By the time leaves begin to unfurl later this month, fertilized female flowers will have elongated into long, drooping stalks bearing small pink samaras, winged seeds that will ripen, drop and whirl to the ground in April.
Those seeds can quickly germinate in a wide range of soils and conditions, helping red maple become one of the most abundant trees in eastern North America. The tree is capable of adapting its root structure to grow in anything from swamps to rocky hillsides. It is, however, susceptible to numerous diseases and is highly vulnerable to damage from fire and sapsuckers, woodpeckers that trigger damage when they tap sap.
One leaf disease might be thwarted by climate change. A Duke University study revealed that infections of a certain fungus were less common and less severe in red maples exposed to higher-than-normal concentrations of atmospheric carbon dioxide. Those conditions made leaf chemistry less palatable to the fungus and caused leaf pores to reduce the size of their openings, making it harder for the fungus to enter the leaves.
But global warming may not be a total boon for the tree. An unusually warm February such as this year's can encourage fruits to develop too rapidly and fall victim to the freezing temperatures that might still be part of the March mix.
A longer growing season could also imperil red maples in the fall if the trees are still green when the first killing frost hits. That would prevent the maples from retrieving critical nutrients stored in the leaves.
SOURCES: Ohio State University Extension, Oak Ridge National Laboratory, Arnoldia, Global Change Biology, Duke University, U.S. Forest Service
March 13, 2012
Appraising urban parks
The Trust for Public Land used the following sources: U.S. Forest Service; University of California at Davis; Water Resources Council; U.S. Army Corps of Engineers; a random-digit-dialed telephone survey of D.C. residents; Chenoweth & Associates/Health Management Associates; John Crompton, Texas A&M; public records; Washington Convention and Tourism Corp.; Dan Stynes, Michigan State University