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Bioinvasion: From Old World to New
National Geographic Today producer Chad Cohen spent more than two months investigating the biological threats posed by non-native species in the United States. His three-part series on the subject airs on the U.S. National Geographic Channel on January 23, 24, and 25 at 7 p.m. EST. The following is a transcript of part one of Cohens series.
European starlings, introduced to America by an avid Shakespeare fan in the 19th century, now number in the millions. (Linda Richardson/Corbis)
Shakespeare compared sparrows to angels that could awaken dreamers from feathery beds. He mused on larks singing at the gates of heaven and the love songs of robins.
Birds of all feathers flutter throughout the works of the bard. From the majesty of their flight to the sweet sounds of their songs, the imagery they evoked captured the imagination of generations. So much so that, in 1890, an eccentric New Yorker and Shakespeare fanatic named Eugene Schiffelin felt compelled to introduce all the birds of Shakespeare to the United States.
In the 1800s, there was a lot of this, a lot of societies bringing things over, says Joe DiCostanzo, a bird specialist for the American Museum of Natural History.
DiCostanzo says Schiffelin was not the only person to share the flora and fauna of the Old World with the new. Immigrants tried to introduce all kinds of birds, plants, and animals in the late 19th century to remind them of home.
Most of [the bio-introductions] dont work; most of them die out; they just dont fit in, says DiCostanzo. But some of them did. Unfortunately some of them did too well, things like starlings, I see starlings flying by us right now.
The starlings ability to mimic human speech earned the bird this cameo in Shakespeares Henry IV:
The king forbade my tongue to speak of Mortimer. But I will find him when he is asleep, and in his ear Ill holler Mortimer! Nay Ill have a starling shall be taught to speak nothing but Mortimer, and give it to him to keep his anger still in motion.
It is the only mention of the starling in all of Shakespeare. Yet it was enough to inspire Schiffelin to import 60 of the fruitful birds to the United States and release them one March day in New Yorks Central Park.
The very first nests were here, under the eves of [New York Citys] Museum of Natural History, says DiCostanzo, And from those first few starlings, [which] might be considered the Adam and Eve of North American starlings, we now have 200 million.
These 200 milliontogether with their other feathered friends like house sparrows, and pigeonsmake up the majority of the birds most Americans see everyday. None of these are native to the United States.
The invaders compete for food with native birds like purple martens and eastern bluebirds, which have been pushed to the brink of extinction. Since the locals tend to fly south for the winter, the foreign birds that are here perenially have an advantage when it comes to nesting spots.
Theres no place for the native birds to come back after their migration, explains DiCostanzo. They just get forced out and if they cant nest, eventually the population is going to go down. And thats been one of the big problems.
Its a big problem that hasnt just been left to the birds. Every boat and plane to cro ss the ocean creates a new opportunity for hitchhikers from around the world to gain a foothold here.
Theyre called invasive speciesand they cost the United States an estimated U.S. $125 billion every year. Schiffelins bird shipments helped launch a century that has seen invasive species irrevocably alter continents and destroy native wildlife.
Red fire ants were brought in from South America in the 1930s as stowaways in the soil of potted plants or in the ballasts of ships. Now the aggressive ants, named for the fiery stings they inflict, march on more than 300 million acres of the southern United States, costing billions of dollars in agricultural losses and ecological damage.
Melaleuca trees are a threatened species in their native Australia. They were brought in to drain the Florida Everglades in the 1950s, and now infest nearly 500,000 acres of wetland. Longhorn beetles from China and Korea embed their larvae in the wood of shipping crates. Once here they attack hardwood trees like maples and elms, which have cost millions of dollars to remove.
U.S. farmers like Jamie Jamison lose between five to eight billion dollars annually to invasive pests through crop damage, loss of grazing land and the cost of pesticides. On Jamisons farm in Maryland one of the biggest problems is a weed called Johnson grass.
Well, it costs money, [to combat the Johnson grass] but if I dont do it and I dont grow anything, Ive got nothing to sell! says Jamison.
Its not always easy to pinpoint exactly where an invasive pest originates and how it gets from one place to the next. Johnson grass is believed to have come from the Mediterranean, brought to the United States as a foraging crop for cattle.
You look at that sucker, says Jamison, just how healthy that is. A good healthy plant, no decay whatsoever, very, very viable and these are one of the problems we have with controlling it its prolific. I wish I could get some of that into some of my other grass species, namely corn.
As hardy as Johnson grass is, Jamison and his corn-growing neighbors like Drew Stabler are able to keep the weed under control if they spend enough on herbicides to keep it down.
If we dont, we know that theres no possible way to be profitable, says Stabler. Its enough of a struggle anyway in agriculture at this point to be profitable growing crops.
Across the Chesapeake Bay, on Marylands Eastern Shore, farmers are faced with a pest of a very different kind.
[The rodent] nutria will frequently travel from marshes into agricultural fields at night and feed on corn crops, feed on soybeans, says Mark Sherfy of the U.S. Fish and Wildlife Service.
In Maryland their major impact hasnt been to cropland but fragile wetlands. The rodents are said to be able to chew through a quarter of their body weight in wetland grasses everyday. Mark Sherfy and Robert Colona are government biologists whove witnessed how destructive they can be.
Nutria feed on the roots of the bay grasses where most of the energy is stored. They chew until whole areas of marshland are barren. Once theyve exposed the ground underneath, the marshes start to erode.
What youre left with is a large mud flat that gets larger and larger and larger until you progress out into open water, says Colona.
When the grasses are gone, there is no way theyll be able to grow back on their own.
This looks real nice aesthetically, explains Colona. Its real pleasant to see this large expanse of lake. But when you think about an ecosystem and how it functions and realize that this was once a very functional marshland system, its pretty alarming.
Back in the 1940s and 50s, fur was in and so was nutria. They were brought to Maryland from their native South America to boost the local fur-trapping economy. But the market for nutria fur was fleeting and the experiment in Maryland was shut down after only a few years.
Part of it is truth in advertising laws that were instituted in the 50s and you had to call a skunk a skunk and a nutria a nutria, says Colona. And demand for those pelts declined.
No one knows for sure exactly how it happenedwhether nutria were released or escaped. But thousands of the beaver-sized rodents are now thriving throughout the Chesapeake and thousands of acres of precious wetland have vanished as a result.
This has helped to rally public support behind a program to eliminate nutria from the bay. Mark Sherfy, who coordinates the program, says its an effort that is also boosted by the nature of the animals themselves.
The furry factor is not real high for nutria, he says. Its not an animal that has a high aesthetic value, and so theres not a lot of emotional value thats attached to the animal.
But invasive species arent always an ugly duckling and emotions can run high against efforts to remove them. Mute swans were brought to Chesapeake Bay from Europe to grace the ponds of large estates with their courtly beauty. During a major storm in March of 1962, high tides and strong winds enabled five swans from this estate to escape.
Its just a matter of numbers and exponential growth over time, says Larry Hindman of the U.S. Department of Natural Resources. The breeding population gradually increased. They have a high reproductive output. They have no natural predatorsby the 1990s the population just began to spike and now weve got about 4,000 birds.
Four thousand mute swans means Maryland has the biggest mute swan population in the country. Unlike most other bay birds, theyre here year round. Waterfowl specialist Larry Hindman is heading a project to determine their impact and what actions the state should take.
We are already seeing conflicts with native wildlife, he says. There are ecological impacts of the swan on the limited baygrass supply and on their competition with native waterfowl.
When it comes to beautiful birds like mute swans, state officials who might want to control them have to contend with much more than the birds themselves. Over the years mute swans have worked their way into the hearts of many of the residents who are against any efforts to get rid of them.
Theyre so nice. Theyre so gentle. They dont make any noise. Theyre quiet, says Maxine Ritter, local resident and swan lover. They just float around and they dont cause any harm.
Mute swans are treading the fine line that distinguishes what may be just an innocuous exotic species from an invasive one. For now theres no way to predict which way theyll go.
I just love them. Gods creatures, how can you fuss with Gods creatures? says Ritter.
But people have been fussing with Gods creatures for thousands of years by whim, by accident and sometimes with the most noble of intentions.
I dont know how [Schiffelin] would feel knowing that the bird he introduced with just 60 birds in central park has become 200 million, concludes DiCostanza. He might feel hes accomplished his goal of bringing this bird of Shakespeare over here. The starling is probably more familiar to people now than Shakespeare...in a lot of the country.