Urban Jungle

Callery pear

Pretty tree going rogue

At the margins of the city, commuters can't help but notice tight groves of white-blooming trees in sunny waste areas, old fields and roadsides.

A first glance, the trees might appear to be cherries, which bloom at about the same time and have similar five-petaled flowers. However, these are more likely to be thorny and aggressive escapees of Callery pear, the seeds of which were probably flown in by starlings engorged with the tree's pea-sized fruits.

The Chinese native hasn't always been so invasive. In 1962, the USDA made commercially available a thornless variety of Callery pear, naming it Bradford pear. The tree, hailed for its bright-red autumn foliage and profuse spring blossoms, was widely planted as an ornamental in the United States. It was unable to fertilize itself and therefore couldn't yield fruit. But as the trees matured, they began splitting apart in windy weather and heavy snowfall.

That disappointment inspired horticulturists to develop new varieties of Callery pear that were able to grow up and weather storms. However, this injection of genetic diversity allowed cultivars of Callery pear to cross-breed and fertilize one another, yielding fruits that would transform a once tame and thornless tree into a problem weed that stabs anyone who gets too close.

SOURCES: USDA, Biological Invasions, BioScience, Virginia Tech

March 27, 2012

American robin song

It takes a night owl to beat the early bird

People rising very early in the morning may hear the pre-dawn singing of American robins. Urban robins crank up their loopy warbling music even earlier than their rural counterparts.

Although city noise might play a role in that — an early start helps urban birds avoid the din of rush hour — it's more likely that they are responding to light pollution.

In 2003, biologist Mark W. Miller studied robin song starting times in Arlington's Lyon Park neighborhood and compared them with data collected from the same location in 1929.

In '29 the first robin songs began about 45 minues before sunrise, but 74 years later, when Lyon Park nights were awash in electrical light, robins tended to break their silence more than an hour earlier, often before any hint of dawn.

Miller's study also included robins near the White House, in an area with even higher levels of artificial light. Those robins began singing about 3 hours earlier than the '29 Lyon Park robins.

Miller said that the starting times for White House robins might be even earlier, because sometimes they were already singing when he arrived to monitor them.

First morning song of American robins in Lyon Park

DURING BREEDING SEASON

*The half-hour before sunrise or after sunset; car headlights are generally not required.

SOURCES: Mark. W. Miller, University of Alaska at Fairbanks; "Apparent Effects of Light Pollution on Singing Behavior of American Robins," the Condor; Biology Letters, the Royal Society

April 10, 2012

Explosive bittercress fruits

Most people associate early spring with flowers and tender vegetation, not ripening fruits. But for hairy bittercress, which began flowering in early February, it's seed-slinging time!

Anyone pulling bittercress from the garden this time of year has experienced the half-foot-tall weed's assault of seeds. Botanists use the term "ballistic seed dispersal" to describe the explosive nature of ripened bittercress fruits.

The pods, or siliques, consist of a central membrane flanked by two outer strips, or carpels, with about 30 seeds in between.

As cells on the outer surface of each carpel dry out, they shrivel, creating tension on the exterior face of the carpel. Meanwhile, the inner surface of the carpel is kept moist and plump by adjacent mucilage.

When cells at the bottom end of the carpel finally give way, the carpel snaps into an upward curl, propelling seeds as far as 16 feet — an effective strategy for spreading into new areas.

Bittercress reaps another benefit from ballistic seed dispersal: An insect climbing onto a ripe silique, with the intention of making a meal out of it, may suddenly find itself catapulted several feet away, far from its would-be meal.

SOURCE: "The mechanism for explosive seed dispersal in Cardamine hirsuta (Brassicaceae)," American Journal of Botany

White oak pollen: job done

They are clogging your gutters, carpeting your decks and landing in your salad at that outdoor cafe. White oak catkins are being shed by their trees after concluding their pollen release for the season, much to the relief of people tortured by oak allergies.

Warm spells followed by cool temperatures and low humidity created ideal conditions a couple of weeks ago for the three-inch-long male flowers to release their golden-green dust, a process that each flower accomplishes in two or three days.

Breezes deposit only a wee fraction of the airborne pollen onto the freshly emergent and inconspicuous female flowers that now appear on the stems of new oak shoots.

A pollen grain fortunate enough to land on a female flower's pink stigmas will sprout a pollen tube that grows toward the ovary to fertilize an egg, which could develop into a ripe acorn that will drop in early September.

When open air space among the oak branches is no longer needed for fertilization, young oak leaves rapidly expand, and the spent catkins float to the ground to gather in drifts, turning rusty brown as they decay.

Before July, next year's catkins will begin forming inside buds on the oak's twigs. By autumn, the packed catkins will be mature, poised to expand in the spring of 2013 to discharge yet another round of blond powder.

SOURCES: Forest Science, U.S. Forest Service, "The Ecology and Silviculture of Oaks," staff reports

White oak catkins (male flower stalks) with details of a male flower and its open pollen sacks, lower left, and a female flower, lower right.

April 24. 2012

Inchworm on a thread

Suspended by a barely visible silk filament, a small green caterpillar dangles underneath a box elder tree.

It's a geometer moth larva, otherwise known as an inchworm, named after its distinctive looping and lunging gait. The caterpillar appears to measure its path in units of its own body length.

But a climb back up a silk line happens at a much slower, steadier pace, as the inchworm uses only its front three pairs of legs to hoist itself back up to the leaf from where it leapt.

Inchworms don't bungee jump for kicks; they reserve that option for escaping predatory insects. Inchworms have lousy eyesight but are quite adept at detecting vibrations, especially those made by the wasps and predatory stink bugs that hunt them.

Testing inchworm sensitivity, entomologists Ignacio Castellanos and Pedro Barbosa used a machine to imitate various oscillations caused by wind, rain, birds, herbivores, wasps and stink bugs. Bird vibrations caused the caterpillars to remain motionless and try to blend in with the plant. But predatory insect vibrations inspired inchworms to anchor a silk line and bail, using long lines to avoid wasps, shorter lines to escape stink bugs.

Some parasitic wasps, however, are aware of the maneuver. They can locate the silk line and either reel up a desperate caterpillar or slide down to inject eggs inside it; the wasp larvae then slowly consume their host.

Sources: Pedro Barbosa, Department of Entomology, University of Maryland; Animal Behavior; Annals of the Entomological Society of America; Invertebrate Survival Journal; Ecological Entomology

May 1, 2012

The bluer a robin egg, the better

Not much point in looking around for a nearby nest when you find an American robin eggshell on the sidewalk.

Soon after a chick hatches, the female robin grabs the eggshell and flies off to drop it far from the nest. Leaving the baby behind for a few moments is worth the risk, since the bright white insides of the eggshell can attract predators.

But before the egg hatches, blue-green pigments on the outside surface of the egg might help with camouflage. Pigments might also strengthen the egg and help protect it from solar radiation.

A robin coats her eggs with the same turquoise-hued compound found in our bile and bruises, biliverdin, an important antioxidant. Female robins with higher concentrations of biliverdin in their tissue lay darker, more vividly colored eggs, which apparently sends a strong signal to males.

"Males seem to use egg color to gauge the quality of their mate and the eggs she lays, putting more effort into rearing babies when they are more likely to survive and prosper," says Robert Montgomerie of Queen's University in Canada.

With Philina English, Montgomerie determined that when eggs are more colorful, male robins will invest as much as twice the amount of energy helping feed nestlings.

SOURCES:Behavioral Ecology and Sociobiology; Bird Coloration: Function and Evolution; Stanford University

May 15, 2012

Silver maple: a better source for ethanol

As a spring storm advances, winds plow through the branches of a silver maple, rolling over the leaves to reveal their silvery-white undersides.

The flash of silver, for which the tree was named, could also be signaling its potential wealth as a resource for biofuels made from cellulose, the fibrous carbohydrate molecule found in plants.

Ethanol made from corn starches is currently cheaper to make than cellulose ethanol. But it yields only 26 percent more energy than is used in its production. Cellulose ethanol yields 80 percent more energy than is used to make it, with net-contribution of greenhouse gases.

Silver maple is an ideal source of cellulose. It can be planted in a wide variety of sites. The tree sprouts profusely after being cut, "is a fast-growing species and is relatively pest-resistant," says Eric Holzmueller, from the Southern Illinois University Department of Forestry. "In order to produce the maximum amount of biomass over time," says Holzmueller, "the species would be planted in a plantation, in rows like corn."

Silver maple trees spaced about 11 feet apart can, after three years, yield 6.3 dry tons of biomass per acre annually, potentially producing more than 500 gallons of ethanol.

Saplings, ground into pellets, can be sent to a biofuels plant, where enzymes from microorganisms break the cellulose into sugars, which are fermented to produce ethanol.

Silver maple might help lead us into clean energy independence, but it is a lousy tree for landscaping. Its roots can penetrate and clog water systems, and although its rapid growth is desirable for making shade, the wood is weak, brittle and prone to rotting, causing many limbs

and twigs to shed from mature trees after heavy snowfall and during windy storms.

SOURCES:Department of Energy, National Plant Diagnostic Network, Oak Ridge National Laboratory, Genera Energy, Microbiology and Molecular Biology Reviews

Peirce Mill restoration bears fruit

A 19th-century apple orchard begins the first phase of its return to Washington this month at freshly restored Peirce Mill in Rock Creek Park.

Three winesap apple trees will be in the ground by June, and as many as two dozen will follow in the next year or two. The Peirces grew winesaps in their orchards flanking Rock Creek in the mid-1800s.

They also sold trees from a nearby nursery. An 1857 Peirce catalogue listed about 50 varieties of eating and cider apples, says Steve Dryden, author of "Peirce Mill: Two Hundred Years in the Nation's Capital." That number "may seem large," says Dryden, "but such breadth was normal in the 18th and 19th centuries, when orchardists and the public relished a floral diversity developed over the centuries."

"Almost every farm had an orchard, as hard cider was preferred to water — safer, it was thought — though the easy availability helped produce a very boozy atmosphere in our country."

Dryden assumes that the Peirces made hard cider and brandies from the fruits they harvested. A stone house near the mill was known in Peirce family lore as "the distillery."

The new orchard is a project of the Friends of Peirce Mill. Students from the District's Harriet Tubman Elementary School will help with planting and upkeep of the trees. "We hope they will be involved in the care of the orchard for years to come," says Dryden, program manager for the nonprofit group, which raised $1 million to restore the mill.

"We may do demonstration apple-pressing to make fresh cider at some point," he says.

Meanwhile, after a decade-long restoration, Peirce Mill — the only operational water mill in Washington — is once again grinding corn and wheat. Demonstrations of the milling process are scheduled for May 23 and 31, and June 6.

Owned and managed by the National Park Service, Peirce Mill is open 11 a.m.-4 p.m., Wed.-Sun.

Privet

The scent of commencement

For many students, their first breath of summer freedom is thick with the heavy fragrance of white-blossomed Ligustrum, or privet, which is commonly planted on school campuses. Perfuming many an outdoor graduation ceremony, the scent invites attendees to close their eyes and drift into a languid torpor.

Privet odor has a stimulating effect on moths, which at night will actively seek out the highly visible flowers. During the day, bees and butterflies are also drawn to the nectar-laden blooms in May and June.

Scientists have closely studied the alluring effect that privet perfume has on the small cabbage white, an invasive butterfly from Europe, Asia and North Africa.

More than 30 compounds comprise the plant's floral scent, and five of those chemicals attract the cabbage white. Two of the most powerful attractants are well-known aromatic compounds:

• Phenylacetaldehyde, also found in chocolate, has a honeylike odor. Scores of insects generate the compound on their own to communicate with other insects.

• Phenethyl alcohol has an aroma that is also present in orange blossoms and in the flowers of hyacinths. The compound, used as a fragrance in personal care products, is also deployed by many insects as an attractant.

Although each chemical by itself can attract cabbage whites, the most powerful draw happens when all five compounds are combined, creating a synergistic effect.

The butterfly reveals its interest by uncoiling its proboscis, anticipating a sip of late spring's dizzy nectar.

SOURCES: Journal of Chemical Ecology, Environmental Working Group, pherobase.com

Black-crowned night herons

Wild wading birds nest at the National Zoo

Every day at 2 p.m., scores of black-crowned night herons collect under a tree near the Bird House at the National Zoo. The night herons, each about two feet tall, gather to compete for freshly killed mice, which zookeepers toss to them. A red-shouldered hawk also flies in from the neighborhood to grab a freebie.

Night herons are capable of finding food on their own, but the zoo uses the mice to create a distraction while some of the larger, less agile captive birds are fed. Otherwise, the night herons would descend into the open pens and steal mice from the fenced-in storks and ground-bound, cranelike bustards.

In early March, night herons arrive at the zoo from perhaps as far away as Central America to build their nests in the trees near the Bird House. They've nested there since at least the early 1970s. It's a safe spot — and there is free food.

Night herons generally sleep during the day and vacate the zoo at dusk, flying off for nighttime feeding excursions at local wetlands, where they fish and hunt for small animals. When night herons return to the nest, they regurgitate some of their catch into the mouths of their hungry chicks, which hatch in April.

By early June, young birds are leaving the nest and are learning from their parents how to hunt — and how to watch for the approach of humans carrying a stainless-steel pan filled with mice. Daily feedings continue through mid-August, when the night herons start migrating to points south.

SOURCES: National Zoo, staff reports

Cichorium intybus

June 12, 2012

Chicory

Do its blue blossoms point to green fuel?

Anyone hitting the highway on a June morning is bound to see the sky-blue blossoms of chicory flanking the roadways. Travelers departing at noon may miss out on the "blue daisies," as increasingly bright sunlight will close the flowers.

Each flower opens only once, but a chicory stem may sport numerous buds, each at a different stage of development, so chicory will continue to bloom throughout the summer.

A European native, chicory is a tough perennial that thrives on the sunny, well-drained soils of pastures and highway shoulders. The plant relies on a deep taproot to hold reserves of carbohydrates for next year's growth.

Most parts of the plant are edible, although people should avoid harvesting plants from potentially polluted roadsides. Slightly bitter flowers enliven salads. Leaves, high in Vitamin C and folic acid, are best eaten raw before the plant flowers; parboiling them in summer removes some of their bitterness.

The taproot, cooked like a parsnip or roasted for use as a coffee substitute, stores energy in the form of inulin, a carbohydrate safe for diabetics. Unlike starches, inulin can't be broken down by human enzymes, but it does stimulate gut bacteria, promoting healthy bowels. Inulin also increases calcium absorption and lowers blood cholesterol.

Besides being healthful for humans, chicory could prove to be good for the atmosphere. Japanese researchers have demonstrated that two fungi used in tandem can quickly turn inulin into ethanol, a process that one day may yield enough carbon-neutral biofuel to power many a summer road trip.

Rapid fermentation of chicory inulin

ETHANOL CONCENTRATION in inulin solution inoculated with fungi

Sources: Plants for a Future, Louis Bonduelle Foundation, Mayo Clinic, Applied and Environmental Microbiology, USDA, Argonne National Laboratory, Ohio State University

Two fungi, Aspergillus niger 817 and Saccharomyces cerevisiae 1200, added to a lukewarm broth of chicory inulin and water, convert almost all of the inulin into ethanol within three days. The 42-proof mixture (21% ethanol) can be distilled into fuel.

Occasionally performing on bright, sunny surfaces, the picture wing fly at first glance looks and runs like a medium-size ant, but the insect appears to have a tiny gas mask for a head, and from its back rise two harlequin wings that slowly row the air.

When the fly finds a prominent spot to show off — such as on a stack of artificial sweetener packets — each of its two boldly patterned wings will move independently, delivering a miniature semaphore message for another picture wing fly to decipher.

The flies appear at many outdoor venues, so a cafe with planters is as good a place as any to perhaps catch an act. The fly will show no interest in your food, as it prefers the juices of decaying plants.

Rotting vegetation is also where the fly lays its eggs. Larvae feed for about a month, pupate for another couple of weeks and emerge as adults throughout the summer months. When the weather cools, late-season larvae slow their development, crawl deep into the humus and drift into quiescence for the winter. Next May, warm temperatures will inspire larvae to squirm to the surface, undergo metamorphosis and emerge for another round of summer antics.

SOURCES: Journal of Insect Behavior, Annals of the Entomological Society of America, University of Florida Institute of Food and Agricultural Sciences