as explained here.
Monday, April 16, 2012
Wednesday, November 02, 2011
|Quagga Mussel / USGS Photo|
One way is through food availability:
Gary Montz, an aquatic invertebrate biologist with the Minnesota Department of Natural Resources, said, "If we see a disruption in the base of the food chain by extremely high densities of zebra mussels, this could impact food for larval fish. That in turn could impact other aquatic life that depend on such fish."
That includes fish-eating birds -- loons, mergansers, grebes, cormorants, scoters and gulls.
|Zebra Mussel / USGS Photo|
"Zebra mussels have a connection with avian botulism," said Carrol Henderson, superintendent of non-game wildlife for the DNR. Botulism is a byproduct of mussel waste. The waste is eaten by fish, which then can infect fish-eating birds.
Thousands of birds in the eastern Great Lakes have died of botulism poisoning since 1999. Species again include loons, mergansers, grebes, cormorants, scoters and gulls.
Some species of diving ducks eat the mussels. Zebra mussels have been a dominant food consumed in the eastern Great Lakes by greater and lesser scaup and bufflehead ducks. Concentration of trace elements in the mussels kills the birds.
The scaup population fell from an estimated 7.5 million breeding birds in the 1970s to fewer than 4 million in 2005, according to author James H. Thorp. The figures come from his book "Ecology and Classification of North American Freshwater Invertebrates."
Tuesday, August 23, 2011
Actually, the Eurasian collared dove has been cropping up in Oregon since 1998 or '99 and, according to local Audubon Society records, it first was spotted in Corvallis in 2007. But now the bird's mid-valley numbers really seem to be taking off.In that case, we might be seeing quite a lot of these in New Jersey fairly soon.
"This is something new," said David Mellinger, vice president of the Audubon Society of Corvallis. "They reached Corvallis a couple of years ago, and suddenly they're all over the place. It seems to be good habitat for them." ...
Although Eurasian collared doves feed on grains and seeds, there have been no reports of crop damage so far, according to the Oregon Department of Agriculture. It's not yet clear whether the new arrivals pose any threat to native species such as mourning doves and band-tailed pigeons.
"The jury's still out on that one," said Rick Boatner, who tracks invasive species for the state Department of Fish and Wildlife. "But it does appear they're expanding their range in Oregon." ...
"It's kind of an interesting story," said Cornell's David Bonter, director of Project FeederWatch, which monitors bird numbers across North America....
By the early '80s, Eurasian collared doves were breeding in Florida, and they soon established themselves in the Southeast.
"Then, between 2000 and 2007, they made this remarkable expansion from Florida all the way to the Pacific Northwest. Now they're found from Florida all the way to Alaska," Bonter said....
Like a couple of earlier European invaders, the starling and the house sparrow, the Eurasian collared dove is highly adaptable and does well in urban environments, two factors that help to explain its rapid advance across the United States, Bonter added.
"They're a bird that really does well in human-modified landscapes, and we've done a good job of making the world friendly to Eurasian collared doves," he said. "There's no doubt in my mind that the Eurasian collared dove will continue to expand and will become one of the most common birds at backyard bird feeders."
Saturday, June 11, 2011
Mugwort (Artemisia vulgaris) is an herb native to Europe, Asia, and Africa that was introduced to North America. It is not particularly eye-catching; instead it appears as a waist-high, gray-green plant. (See a line drawing for identification.) In its native range, it was traditionally used as a substitute for tea (when tea was extremely expensive) and as a treatment in Asian medicine. In North America, its propensity to grow in dense clumps and spread quickly makes it highly invasive, and it can take over disturbed areas quickly. Once it gets established, it is very difficult to remove.
Saturday, January 09, 2010
The Eastern Gray Squirrel (Sciurus carolinensis) is a relatively recent addition to the fauna of the British Isles. The species's rapid spread has led to fears that it will displace native fauna that are already under pressure. According to one recent study, recent declines in the U.K.'s woodland birds are not being caused by the introduced gray squirrels.
BTO ecologists Dr Stuart Newson, Dr David Leech and Dr Chris Hewson and NE's Dr Humphrey Crick and Mr Phil Grice examined 38 bird species associated with woodland, including common starlings, wood pigeons, wrens, woodpeckers, thrushes, warblers, tits and finches....Of course, the study does not rule out negative effects on species not included in the study, such as hawfinches. It also does not negate the very real problems that gray squirrels are causing for Britain's native red squirrels (Sciurus vulgaris).
Of the 38 bird species, a statistically significant relationship between grey squirrel and bird population sizes was found for 12 species.
Of those, squirrels appeared to have a positive impact on seven bird species, a correlation probably caused by both mammal and bird species benefiting from similar changes to their habitat.
Grey squirrels had a negative impact on just five: the common blackbird, Eurasian collared dove, green woodpecker, long-tailed tit and Eurasian jay.
"Of these species, the most convincing evidence is for blackbird and collared dove," says Dr Newson.
For these two species, the researchers found a weak but significant relationship between the abundance of grey squirrels and a failure of the birds' nests.
However, while grey squirrels may be predating on these two species, the overall number of blackbirds and collared doves has gone up nationally, and even locally where grey squirrels are common.
Monday, August 31, 2009
The St. Lawrence Seaway, the major shipping canal connecting the Atlantic Ocean with the Great lakes, has become a major conduit for invasive species. About a third of invasives in the Great Lakes region have come by that route, and many of them end up elsewhere in the continent.
Zebra and quagga mussels from the Black Sea clog intake structures for municipal water systems and power plants. The mussels also gobble plankton so voraciously that little is left for other organisms. Round gobies and other invasive fish beat out native fish for food supplies, harming the lucrative commercial and sport fishing industries. Ballast is even blamed for the emergence of viral hemorrhagic septicemia, often called "fish ebola," resulting in large fish kills in the past several years.Many of the invasive species have come through ballast, which is not well regulated.
And as infected pleasure boats are hauled to other lakes or species swim and float into tributaries, or even the Mississippi River, invasive species that came in with the ballast are spreading throughout the United States. Large quagga and zebra mussel colonies have been found in California and Nevada and are threatening to spread through California's many miles of municipal water pipes.
There are no federal standards for ballast treatment, although the Environmental Protection Agency and the Coast Guard are working on requirements that should reduce the amount of live organisms in ballast water.Stricter regulations are supposed to be on the way, but have been slow in coming.
Since 1993, ships have been required to exchange their ballast in the Atlantic before entering the Seaway, replacing water from whatever port they had last visited with high-seas water containing little life.
But until 2008, U.S.-bound ships loaded with cargo and hence containing no ballast were exempt from any regulations. These ships are called NOBOBs, for No Ballast on Board. But their "empty" ballast tanks contain many tons of muddy slop teeming with bacteria, small marine organisms, eggs and larva.
NOBOBs typically unload their cargo -- often steel -- in Great Lakes ports like Detroit and Cleveland, suck water into their ballast tanks, then head to other Great Lakes ports -- Duluth, Toledo or Milwaukee -- to load up on grain and dump their ballast, now mixed with the biologically rich mud.
Sunday, August 16, 2009
The box shown above is one of several such purple boxes hung from trees around Hacklebarney State Park, near Chester, New Jersey. The boxes are part of a USDA survey for Emerald Ash Borers. These beetles are not originally from North America; instead, they arrived from eastern Asia sometime prior to 2002, when the first specimens were discovered in the Detroit area. Since then it has spread to 10 states in the Midwest and Mid-Atlantic regions.
This species poses a serious threat to native ash trees, potentially rivaling the destruction caused by Chestnut blight and Dutch elm disease in the last century. The USDA website on the emerald ash borer describes their potential impact:
Emerald ash borer is a serious pest and quarantines are established around infestations. Larvae feed in the phloem and outer sapwood producing galleries that eventually girdle and kill the tree. This invasive pest has had a devastating impact on communities that now face significant tree removal costs associated with dead or dying ash trees that pose a threat to public safety.The USDA has posted images of the borers and some signs of infestation.
Ash trees are as important ecologically in the forests of the northeastern United States and eastern Canada, as they are economically. Ash trees fill gaps in the forest and provide shade for the forest floor. They are very desirable for urban tree planting because they grow well under difficult conditions. Ash wood is valued for flooring, furniture, sports equipment (e.g., baseball bats, hockey sticks, oars), tool handles, and supplies for dairies, poultry operations and beekeepers.
Other repercussions include decreased property values, losses in the long-term supply of ash wood, decreased air quality, increased electricity use during hot weather, and negative impacts on Native American cultures that use ash wood for traditional crafts and ceremonies. In addition, there are other detrimental impacts on wildlife and natural ecosystems. As a vital component of forest succession, ash colonizes and stabilizes disturbed areas. In addition, ash is one of the few native trees able to out-compete weeds that prevent most other species from becoming established.
The potential destructiveness of emerald ash borers is a reminder that we need to be careful about what sorts of plants, insects, and other creatures are introduced to the continent. Unfortunately this is difficult in an era of widespread globalized trade and international travel. It is all to easy for a species to be introduced, either accidentally or deliberately.
Saturday, August 15, 2009
The photo above shows a cluster of Purple Loosestrife (Lythrum salicaria). This flower is native to Eurasia but was introduced to this continent in the 19th century. It has since spread through most of the United States and Canada. While its racemes of purple flowers, this plant's tendency to crowd out native wildflowers has landed it on least wanted lists. It is common in wetlands and along highways and waste areas.
This particular cluster, a large, dense mix of loosestrife and Phragmites australis, seems quite attractive to a variety of insects. (No doubt this attractiveness had aided its spread.) I have included photographs of several below.
First up is a Silver-spotted Skipper (Epargyreus clarus), a species mentioned in a previous post.
Next is what I believe to be a Crossline Skipper (Polites origenes). This was a challenging identification because I only have a shot of the undersides of this butterfly's wings, but it seems to be the best match among species that might be flying now.
Photographing the skippers was somewhat difficult since many of them showed little inclination to sit for long on a single raceme. I caught this Hobomok Skipper (Poanes hobomok) just as it was taking off. (The closely-related Zabulon Skipper was featured in a previous post.) In addition to the butterflies shown above, there were many European Skippers (Thymelicus lineola), as well as a few Orange Sulphurs (Colias eurytheme), Cabbage Whites (Pieris rapae), and Eastern Tiger Swallowtails (Papilio glaucus), none of which I managed to photograph.
The cluster also attracts other insects, such as the wasp above. Wasps are still somewhat beyond my identification skills, so I cannot put a name on it at present. The closest I can find is the subfamily Eumeninae, which includes potter and mason wasps. These are mostly solitary wasps that feed on nectar and kill various insects to feed their larvae. If anyone has a better identification, please leave a comment.
Included in this week's SkyWatch Friday:
Monday, May 11, 2009
Hearings on H.R. 669, the Nonnative Wildlife Invasion Prevention Act, have publicized some weaknesses in how the U.S. handles wild animals brought into the country.
The global wildlife trade generates hundreds of billions of dollars annually. The team analyzed Law Enforcement Management Information System (LEMIS) data gathered by the U.S. Fish and Wildlife Service from 2000 through 2006 and found the United States imported upward of 1.5 billion live wildlife animals. The vast majority of the imports were from wild populations in more than 190 countries around the world and were intended for commercial sale in the United States — primarily in the pet trade....Most of the linked article concerns the potential effects this lack of regulation has on the spread of disease. Such focus is understandable in light of ongoing concerns over swine flu. However, the uncontrolled importation of wildlife creates problems for ecosystems here and abroad. In the U.S., nonnative species may be introduced into local ecosystems and crowd out native species that fill similar niches. (Many of these native species are already vulnerable due to habitat loss and degradation.) Unrestrained trade deprives other countries of their native wildlife. If the imported animals belong to a threatened species – which border inspectors may or may not be able to recognize – then permitting such trade could hasten the species's slide towards oblivion or hamper its recovery.
The team also found that more than 86 percent of the shipments were not classified to the level of species, despite federal guidelines that mandate species-level labeling. The lack of accurate reporting makes it impossible to fully assess the diversity of animals imported or calculate the risk of nonnative species or the diseases they may carry, the team wrote.
“Shipments are coming in labeled ‘live vertebrate’ or ‘fish,’” Daszak said. “If we don’t know what animals are coming in, how do we know which are going to become invasive species or carry diseases that could affect livestock, wildlife or ourselves?”
H.R. 669 may not be the correct instrument to deal with these problems. It certainly has attracted some very vocal opposition from both scientists and the pet industry. Whether or not this particular bill passes, there ought to be better oversight of what wildlife is brought into the country.
Wednesday, June 18, 2008
Invasive species – plants, animals, or others – pose major problems for native species. Some of the worst cases of invasion come from Pacific islands where many birds that evolved without predators have become extinct or endangered due to introduced mammals. A recent study of bellbirds in New Zealand provides a counter example of birds changing their behavior to cope with an introduced predator.
The study focused on the New Zealand bellbird (Anthornis melanura), an endemic species that was exposed to introduced mammalian predators within the last 200 years. It compared nesting behavior at four types of nests:
- Mainland bellbird nests with introduced predators present
- Mainland bellbird nests with introduced predators removed
- Island bellbird nests with no introduced predators
- Tasmanian honeyeater nests with native predators
This study gives some hope that other native island birds can adapt relatively quickly to the presence of new predators. These particular adaptations are specifically suitable for woodland birds, whose nests can be easily hidden. Seabird colonies and flightless birds face greater challenges in protecting their nests from predators. The best policy is still to prevent the spread of harmful invasive species or remove them where possible.
Wednesday, February 27, 2008
Credit: Hariet Hinz & Ester Gerber, CABI Biosciences, Bugwood.org
Garlic mustard (Alliaria petiolata) is an invasive plant that is widespread in forests of the eastern United States. When it gains a foothold, it rapidly spreads to cover much of the forest floor and crowds out native plants and the animals that depend on them. It is especially common in disturbed areas or forests with a high deer population. Because the plant reproduces rapidly and its infestations are so widespread, effective controls are difficult to apply.
The tiny insect pictured above, the univoltine root mining weevil (Ceutorhynchus scrobicollis), may provide a solution. The USDA's Invasive Weed Management Unit has been investigating biological controls that could be applied to reverse the plant's spread. The team considered several parasites that attack garlic mustard in various stages of development. The trick was to find a parasite that could keep garlic mustard in check without becoming invasive itself.
The computer simulation was used to select a tiny weevil, about the size of an "o" in 12 point type. "There are actually several weevils that feed on garlic mustard back home in Europe, where it comes from," said Davis. "This particular weevil that we're looking at (Ceutorhynchus scrobicollis) feeds on the plant at several stages in its life cycle so it's a much more effective agent than some of the other ones."If this control method is approved by the USDA, the univoltine root mining weevils could be introduced into American forests later this year. They will have a lot of eating to do.
What happens if the control agent also becomes an invasive species?
"A stringent battery of tests is performed on each biocontrol agent in quarantine before it is ever released. For example, garlic mustard is in the same family (Brassicaceae) as cabbage, so one test might be to only feed the weevil cabbage and see if it survives on it or can reproduce on it. If it does, then the possibility exists that it could move from the garlic mustard and threaten cabbage plants, which we don't want to happen. But, this particular weevil has passed that test for a wide variety of plants."
Davis said that there are different strategies for biological control. One strategy is inundative in which the control agent eats its way through the garlic mustard and then dies out itself because there isn't anything left to support it. The other strategy is to introduce a natural enemy that will just bring the population down to a lower level and the plants and pests just continue to coexist. "The idea is that you reunite plants with a natural enemy from back home -- which in garlic mustard's case is Europe. In Switzerland garlic mustard and the weevil coexist and neither one is invasive."
Monday, October 08, 2007
Speaking of invasive species, the Times profiled some of the threats facing the widespread forests of New Jersey, New York, and Connecticut. While the acreage covered by forests has increased over the past century, the composition of forests is changing. Many forests occur in smaller plots, many are losing their understory, and invasive plants are replacing native ones in many locations.
From state to state and forest to forest, the situation is variable and dynamic. “There is a lot of healthy forest left,” said Dr. Joan Gardner Ehrenfeld, an expert on invasive species who is a professor in the Department of Ecology, Evolution and Natural Resources at Rutgers University.The various threats are interwoven. Sprawl leads to forest fragmentation, which in turn encourages invasive plants to proliferate. The overpopulation of white-tailed deer also makes it harder for native plants to survive and easier for invasives to take over. Some invasive plants are distasteful to deer, while the native plants are not.
But in some areas, multiple threats “are coming together as a sort of a perfect storm,” she said. “There are too many different problems all converging at the same time in the same place, and the multiple effect makes the situation all the more serious.”
These threats, experts say, include suburban sprawl, the impact of marauding invasive plants and insects, climate change and not only acid rain but also, contrarily, lack of rainfall. But in many locales, the implacable browsing of deer on young trees is killing replacement saplings, depleting shade and promoting the growth of invasive plants that smother native species.
In some areas the impact is so profound “that it looks like someone took a brown crayon and used a ruler to draw in a brown line and a green line,” Dr. Ehrenfeld said. “The green above stops at a steady line at the height that deer can reach.” Increasingly, “suburbia is uniquely designed to grow and harbor deer,” Ms. Sauer said, “because lawns and flower gardens are high-quality deer delis, and the deer are safe from hunters.” She added, “We have created a physical environment where there is no limit to their growth.”The disappearance of forest's understory and the proliferation of invasives changes the types of animals that can survive there.
Forests can heal themselves when they have a population of 5 to 10 deer per square mile, “but now 35 per square mile is common, it’s well over 50 in some places, and in a few places in New Jersey it can be 250 or even more,” Dr. DeVito said. “One overabundant species is sacrificing thousands of other species. We have to recognize that, and deal with it.”
And newer invasives are perennially joined by older stalkers. This year some 320,000 acres of New Jersey trees were defoliated by gypsy moth caterpillars, the most since 1990, when more than 431,000 acres of trees experienced leaf loss. A growing concern is the appearance of kudzu, a climbing perennial vine that can reach heights of close to 100 feet and has caused hundreds of millions of dollars in damage to Southern woodlands.
Still, some forest managers fear a future of “boring forests” or “trash forests,” with fewer hardwoods and more species like ailanthus and cottonwoods that may transform the region’s wildlife population.So what types of birds might be affected? The primary impact would be felt by birds that depend on a rich understory for nesting or foraging. These include most thrushes, many warblers (including ovenbirds, black-throated blue warblers, and Kentucky warblers), and fox sparrows, among others. Even some canopy-dwellers, such as cerulean warblers, start to disappear when the understory is lost or degraded. Studies have shown that deer exclosure plots and forests with lower deer density have higher plant and bird diversity.
In the worst case, “we are looking forward to forests that look like the landscapes of vacant lots,” Ms. Sauer said. “Alien species, and no complexity. And that level of simplification will affect birds, mammals, butterflies, everything.”
Most forests profiled in the article will continue to exist for the foreseeable future. They occur on large tracts protected as federal or state public lands for conservation and recreation. What they look like in the future will depend on how well the current threats can be managed.
Birders can help with the problem to some extent. One way is to volunteer for invasive species control efforts, if they are available locally. Another is to be careful to use native or noninvasive species for plantings around the home. Here is an invasive plant identification key, and here are tips for control and removal. Local native plant societies can provide recommendations for what to plant and where to find them. Here are lists of sources for native plants for New Jersey and Maryland, for example.
One nonnative invasive tree highlighted by the Times is the norway maple. These tall shade trees have a wide and dense canopy that blocks out most sunlight and rainfall from reaching the ground. As a result, it is difficult for any other plants to grow underneath them. Like a true invasive, norway maples are prodigious breeders. The trees produce seeds (pictured left) twice annually; the lightweight seed packets spread easily.
Norway maples are widespread in Central Jersey. When I was growing up, they seemed to be our characteristic maple. Since then I have learned better and look on them quite differently.
Sunday, October 07, 2007
The phrase "invasive species" calls to mind a plant or animal being imported from Europe or Asia and running wild in North American habitats. The likes of starlings and garlic mustard cause major problems for our native wildlife and for wildlife managers. Sometimes the invasion works in reverse. One example is the gray squirrel, which was brought to England over a century ago. In this country, they are an occasional pest for homeowners and bird feeders but otherwise harmless; in the United Kingdom, they threaten the native squirrel population.
The Lake District, in the north of England, is on the front lines of a new Hundred Years’ War. It is a war between rodents. Since the 19th century, gray squirrels, an American import, have been overtaking Britain’s native red squirrels and claiming their territory. The grays have moved up from the south of England, thinning out the reds along the way. The reds now survive mostly in Scotland and the English counties, like Northumberland, that border it. The grays are larger and tougher and meaner than the reds. They can eat newly fallen acorns, and the reds cannot. They cross open lands that the reds are scared of. They are more sociable than reds, allowing for higher population densities. Although gray males cannot mate with red females, they often intimidate red males out of doing so....Read the rest.
The situation has now reached a crisis point: there are only an estimated 160,000 red squirrels left in Britain, whereas there are more than 2 million grays. Without human intervention, reds could be gone from England in 10 years. The red squirrel is a national icon, and the British government is trying hard to save it. Deliberately killing a red squirrel or disturbing its nest, called a drey, is a crime. Last year the government set up more than a dozen refuges for red squirrels in the north of England.
Wednesday, August 29, 2007
Instead of constant mowing, Delaware is allowing native grasses and flowers to grow along its highways.
Dark green switchgrass stands four feet tall. Asters, amonsia with tiny blue flowers, and flowering white thoroughwort nestle there, in place of a simple lawn. Down the road, the cloverleaf for I-95 and Route 896 is filled with golden Indiangrass, its gossamer flowers riffling as trucks whiz by.The article reviews highway vegetation policies in other states and the problem of crown vetch, first introduced along Pennsylvania highways half a century ago.
This is the meadow vista when Delaware was a colony, and before. Now these regional plantings are increasingly deployed by highway gardeners around the country who see themselves as heirs of an environmental Enlightenment. Their credo: get the mowers out of the 12 million acres of roadsides and median strips around the United States, and let the wildflowers and grasses grow.
In part as a frugal move — not mowing can save states tens of thousands of dollars each year — at least a dozen states including Colorado, Nebraska, Oregon, Texas, Tennessee, South Carolina, Vermont and Washington State , have increased their inventory of native plantings. Roadsides, they say, are the national front porch. Why, then, should they look like an English formal garden or a Scottish golf course? Why shouldn’t they mimic the land as it was before highways?
In the words of the University of Delaware horticulturist, Susan S. Barton, an adviser to the state’s Department of Transportation: “We’re doing it so when you’re driving around Delaware you know you’re in Delaware, not in the tropics.”