Monthly Archives: December 2010
In the past few weeks, the honking flying V’s of Canadian Geese have nearly ceased. Almost all of the geese that are headed south to avoid the harsh New England winter this year have already flown the coop, so to speak. However, many have instead chosen to remain behind and are seeking greener pastures not in the warm southern latitudes like their fellows, but around lakes and fields across the northeast.
Historically, Canadian Geese (Branta canadensis) migrate south from the location of their hatching (throughout the northeastern United States and much of Canada) to their wintering habitats in the southern United States in the fall of each year. The migration allows them to avoid the harshest weather during the winter and competition from other bird species during the summer.
As it would happen, there are a number of potential reasons for this change. Some have been explored by the scientific community more than others, but most of them seem, even those that haven’t been investigated as thoroughly, all seem plausible. Among the possible reasons for this shift from migratory to residential are: A lack of serious predatory threats, an increase in available food during the winter, and the release – many years ago – of captive goose flocks. In all likelihood, it is a combination of these causes – rather than one over the others – that has allowed Canadian Geese to become so widely residential.
To begin, Geese are most vulnerable to predation while they are incubating and raising their chicks. During this time the adult geese shed their flight feathers, effectively grounding them for the duration of incubation. The Geese are vulnerable during this period. However, residential populations are in less danger, due to reduced predatory pressure. The widespread destruction of habitat in the northeastern United States capable of supporting predators like foxes, bears, wolves, and eagles has reduced the pressure on residential populations of Geese that would otherwise be consumed.
The second large change that has allowed Canadian Geese to become residential is also related to changes in the northeastern ecological landscape. The same changes that made the northeast less habitable for predators like wolves or foxes made it a much easier place for browsers like geese to find food. Geese are almost entirely herbivorous, primarily eating grass, and so the spread of suburbs across the Northeast (along with the simultaneous loss of forest habitat) has dramatically increased the amount of food available for them. As a general rule in ecology, any set of circumstances which reduce predators while also increasing the amount of food available to a population will allow that population to flourish and grow. Geese are no exception to this rule, at least one study says that the number of Canadian Geese in the northeastern United States has tripled in the last twenty years.
These two trends go a long way towards explaining why established residential populations of Geese would do so well. However, they don’t manage to explain how the trend began. One theory that makes sense, though it’s unlikely to be the final word in the discussion, is that the release of geese raised in captivity into the wild gave rise to a population that had never been taught as juveniles “how” to migrate (the behavior is learned, not innate). Because of recent changes in the ecology of the northeastern United States, those geese that were unable to join their fellows in the southern United States survived to reproduce. The wild born offspring of the captive raised geese were never “taught” how to migrate either, continuing the cycle.
Canadian Geese are native to North America. However, never before have they been residential. In the United States the changes wrought by their continued presence are minor. Other countries however, are not so lucky. In Australia and New Zealand for example, they are currently considered invasive. With the rapid growth the American Residential Canadian Geese populations have been experiencing, it could be possible that – at some point in the future – they become more than the annoyance they are currently. Luckily, research is already ongoing on ways to cull out of control goose populations, should the need arise.
Zebra Mussels (Dreissena polymorpha) are an invasive mollusc species, native to the Black Sea, that has – since its introduction to North America in 1988 – spread into many of Americas waterways with alarming speed.
Over the course of their 5 year lifespan, Zebra Mussels grow to be 1-2 inches long and are yellow with dark “zebra-like” bands running along their shells. They spend the beginning of their lives as free swimming larvae before settling onto an appropriate surface and entering the adult phase of their life-cycle. As adults they’re immobile and rely on their thick shells for protection from predation.
The environmental threat posed by Zebra Mussels can be traced to their amazing success at colonization; in some cases upwards of 700,000 adult mussels have been found on 1 square meter of suitable substrate. Zebra mussels are able to settle and grow on almost any solid surface, much to the detriment of most species around them. Beyond the simple fact that their presence can crowd out other species of shellfish they are highly efficient filter feeders. Filter feeders derive nutrition by pulling small particles of organic matter out of the water. In areas that have been taken over by Zebra Mussels this action can make the water significantly clearer. This change in water clarity can allow other species of aquatic plants, previously absent in invaded lakes and streams, to grow and flourish, and the lack of organic material in the water can cause other species of fish to go hungry.
Beyond the environmental threat is the danger that the mussels pose to boats, underwater pipes, and intake valves. Cleaning surfaces upon which they have established themselves is an intense process which costs millions of dollars a year. Additionally, the shells left over when Zebra Mussels die are sharp and can wash ashore in such great numbers that they completely cover beaches surrounding areas where they are prevalent.
Zebra Mussels were first discovered in Massachusetts in July of 2009 in Lake Laurel. Several Massachusetts governing bodies, including the Massachusetts Department of Fish and Game, quickly drafted a plan to respond to the threat posed by a successful invasion by the molluscs. The object of their initial efforts was largely to contain the invasion while a more comprehensive plan could be drawn up by closing the boating ramps and requiring that all boats be stored out of water for the duration of the season. Unfortunately, these temporary measures did not succeed in containing the spread of the mussels.
Currently there are several ways of dealing with Zebra Mussels. Obviously, manual removal, while effective at removing the mussels from where they have become established, is labor intensive and expensive. Studies have shown that they are vulnerable to high temperatures, and die when the water around them reaches 110 degrees Fahrenheit. Finally, because of the nature of their reproduction some scientists believe that it might be possible to interfere with their ability to breed. If that were to be the case then the state officials currently fighting the spread of Zebra Mussels would have a powerful new weapon to help with their work.
The USDA first confirmed the presence of the Asian Longhorned Beetle in Worcester in early August of 2008. The combined state and federal government’s removal effort is still ongoing, and has — at last count — cost approximately 50 million dollars. This expense – large as it is – constitutes a reliable indicator of just how great a threat the Asian Longhorned Beetle poses to local forests. However, despite the best efforts of the Massachusetts Department of Agriculture, the pest continues to spread across the state. As evidenced by the fact that recently (August of 2010), Asian Longhorned Beetles were confirmed to have entered Boston.
The Asian Longhorned Beetle nests in the living tissue of many native trees – Maples, Willows, Elms, Birches, and Horsechestnuts to name a few – making hollows beneath the bark that can eventually prove fatal for the tree. A full-fledged invasion of Massachusetts’ forests could therefore prove to be extremely bad for the health of local forests, as well as to the survival of the industries that depend on their health for revenue.
Currently, infestations of Asian Longhorned Beetles are dealt with with a combination of strict quarantine measures in infested areas, pesticides containing the chemical imidacloprid, and the removal and thorough destruction of infested trees. The USDA has urged Massachusetts residents to keep a careful eye out for Asian Longhorned Beetles and to continue to honor the policy of not removing wood from the quarantine areas.
As is true for most management efforts, locating members of the target invasive species before they are able to breed in an area is crucial to reducing their numbers. Unfortunately, Asian Longhorned Beetles breed quickly, with females laying their eggs in pits they chew out in the bark of infected trees. Once the eggs mature into larvae, they burrow their way into the living tissue of the tree and enter the pupal stage. Adult beetles emerge the spring following their hatching by tunneling straight outwards through the bark of the tree, creating large holes as they exit their nurseries. Infected trees are easily identified by the presence of sawdust like ‘frass’ littering the bark and the ground around them. This sawdust is generated by the actions of the beetles within the still living tree.
Once detected, the USDA recommends a specific strategy to control the spread and reproduction of the invading beetles. After quarantining the area surrounding the infected trees, all potential host trees within half a mile of the original detection are treated with pesticides. Depending on the severity of the infestation, and on the specific qualities of the forest in question, infected trees may be removed entirely rather than simply sprayed. In this case a replanting treatment follows the eradication of the beetle from the area.
This method of controlling the spread of the Asian Longhorned Beetle has shown itself to be effective –so far — at treating beetle invasions. An Asian Longhorned Beetle infestation in Chicago was effectively removed this way. Hopefully the infestation in Massachusetts will likewise be eliminated. In the meantime, both the state and federal governments urge citizens to continue to report beetle sightings.
As noted in an earlier article, Massachusetts is an unwilling home to a large variety of invasive plant species. Unfortunately, the problem of invasive species is not restricted to just plants. Invasive animal species can be equally detrimental to the biodiversity and health of an ecosystem. Massachusetts, like most other parts of the world, is now host to dozens of non-indigenous and possibly dangerous animal species. Their numbers include the Zebra Mussel (Dreissena polymorpha ), which was originally from Russia and the Asian Longhorn Beetle (Anoplophora glabripennis ), which likely arrived in the US in the wooden boards that made up shipping crates and pallets.
Zebra Mussels are freshwater molluscs that were first detected in the great lakes region in 1988. With no natural predators to curb their population they quickly spread in all directions. Massachusetts was fortunate in that its waterways remained clear of the problematic animal until 2009. In other areas of the country they spread far faster, arriving California – presumably for the first time – earlier this year. Once present in a lake, stream, or river they quickly multiply, eventually completely covering every surface they can colonize. Their huge numbers affect, among other things, the clarity and organic content of the water and the other types of molluscs and fish that can survive in the area. Additionally, they have a tendency to clog the machinery of water treatment and power plants.
The Asian Longhorn Beetle is a large insect with long white and black antennae that only recently arrived in Massachusetts – although it has been present in the United States for several years. It is known for making its home within a wide variety of trees, including Red Maples, Elms, and Willows. These trees have no natural defense against the unfortunate attentions of the Asian Longhorn Beetles and so infestations are typically fatal for the host plant. This past March, following the discovery of a live beetle in Worcester, Massachusetts, the USDA launched an extensive eradication campaign in Massachusetts. Unfortunately, while such campaigns can be locally effective, the species remains at large throughout much of the northeast and, even optimistically, it will likely take years to exterminate fully (if it is possible to remove it at all).
Invasive plant species are exotic, or non-native, plants that are able to grow and thrive in locations different from where they originally evolved. Specifically, invasive species are exotic species that are detrimental to their native neighbors. In some cases, the presence of exotic species in a habitat can have negative effects on local biodiversity and on the health of native plant and animal populations. However, this is not always the case, in part because most species of plants and animals are not able to survive – let alone thrive – when removed from the environments that they are adapted for. As a result, many popular garden plants are “exotic.” However, only a few are ever considered “invasive.”
Exotic species might come to an area for any number of reasons. Often, the term “invasive” is reserved for plants or animals that have been moved to a new area specifically by humans, rather than migrating on their own. The Department of Agriculture recognizes 147 different species of invasive / noxious weeds within the Commonwealth of Massachusetts. Among their number is the ornamental shrub Japanese Barberry (Berberis thunbergii), the biannual herb Garlic Mustard (Alliaria petiolata), and the fast-growing Mile-A-Minute Vine (Mikania cordata).
Japanese Barberry was brought to the USA in the late 1800’s to serve as a decorative hedge for gardens in the north-east. It was quickly found to be shade tolerant, it grows thickly, and it is resistant to deer. Unfortunately, the same qualities that make it a valuable shrub for someone’s backyard also allow it to grow extensively in the forest understory. Its presence in the understory blots out light, which makes it extremely difficult for other plants to grow. Garlic Mustard, which was likely imported as an edible garden plant, flourishes in fringe habitats (like those found alongside highways) and could possibly poison the soil it grows in leaving it uninhabitable for other species of plants. Finally, Mile-A-Minute Vine, first seen in the continental US in Oregon around 1890, is capable of completely covering and killing small trees and shrubs if not removed quickly.
Other invasive plants exist across the world, some species take advantage of niches in the ecology left unfilled before their arrival, others are able to thrive because they have no predators in their new home. Some species are largely harmless. Others, like the three mentioned above, are dangerous not only to the plants and animals directly effected by their presence, but can also negatively impact human activities in areas they have infested. As a result, both state and federal government agencies are devoted solely to the removal of invasive species from areas where they have become prevalent.