ASCENDANT STORIES

Egg, brown-headed cowbird – Molothrus ater

The cowbird is an opportunist that lays its eggs in the unattended nests of other birds. A female cowbird uses trickery to ensure acceptance of her egg; she will puncture and eat, or eject one of the host’s eggs so that when the host female returns, there are the same number of eggs as when she left. If the ruse goes undetected, the host bird will incubate the cowbird egg as part of her own clutch. Cowbird chicks are large at birth and grow rapidly, often displacing their nest-mates and taxing the host parents’ energy and skills. This strategy of finding unsuspecting hosts to incubate their eggs and raise their young evolved so that the cowbird could migrate with the great bison herds that once roamed central North America, freeing them to follow the feast of insects stirred up by the bison. Many species of songbird along the old migratory bison routes learned to recognize and reject a brown-headed cowbird egg. Since the demise of the bison, the cowbird has switched its foraging strategy to sedentary domestic livestock, and its range now includes all of sub-Arctic Canada, the United States, and northern Mexico. This sleight-of-hand artist, free to lay eggs all season long, now parasitizes the nests of more than 200 species, most of which do not recognize a usurper’s egg.

Purple loosestrife – Lythrum salicaria

Imported into the United States in the early 19th century from Europe as a garden ornamental, these stunning spikes of purple flourish in wetlands in every state except Florida. The “purple plague” exhibits all of the major traits that characterize successful invasive plants: early reproduction by seed and shoot; many and easily dispersed seeds that have few special germination requirements; long flowering and fruiting seasons; tolerance of a wide range of climatic and soil conditions; and few if any predators or diseases in its new habitat, two factors that normally keep populations in check.

Cheat grass – Bromus tectorum

Now covering more than 100 million acres of the intermountain west of North America, cheat grass supplies green forage for cattle. This range invader entered British Columbia in 1899 and spread along the path of the railroads. Trains transporting settlers’ livestock carried cheat grass seed mixed in with seed grain, feed, bedding, and animal dung. B. tectorum seeds sprout early and choke out competing native grasses and shrubs. Unlike many native plants, cheat grass burns readily, and its rapid regeneration after fire results in vast monocultures. When cheat grass takes over, there is a drop in the diversity of other plant species and also a decline in populations of small animals like chipmunks, ground squirrels, kangaroo rats, voles, shrews, and mice. Bird diversity drops as well. While there may be eight to twelve species of birds in sagebrush scrub, there may be only one to three in cheat. This is because the native inhabitants rely on a variety of roots, sprouts, and seeds, as well as the contingent insect populations of the more varied sagebrush plant community in order to thrive.

Nutria– Myocastor coypus

Beaver fur is ideal for making felt hats, beaver oil has been used in medicines and perfumes, and beaver tail was once considered a great delicacy. By 1350, all of Europe and much of Russia had been denuded of beavers. Between 1700 and 1900, over 400 million pelts were harvested and exported from America, resulting in an inevitable decline in the number of beavers. In the 1930s a plan was made to import nutrias to Louisiana with the hope of establishing a replacement for the beaver fur trade. These South American rodents, also called coypus, escaped from breeding farms and spread widely, uprooting marshland and burrowing through levees in the southern seaboard states. With no large predators to reduce their population, the nutrias’ vigorous feeding habits are having a significant impact on marsh vegetation, particularly cypress seedlings, and are effectively converting marsh to open water. Efforts by trappers to reduce the burgeoning population had some initial success, but the market for nutria pelts has been depressed since the 1980s, when fur garments were deemed politically incorrect. There is, however, a new angle on abatement being promoted by chefs in Louisiana: nutria jambalaya.

Mongoose– Herpestes auropunctatus

Rats have followed humans throughout time and around the globe, with devastating consequences for many local species, especially on islands. In Hawaii, black rats damage native trees and shrubs. They also eat birds’ eggs, nestlings, and invertebrates, including many beautiful native varieties of tree snail. The Indian mongoose was imported to Hawaii in 1883 in a misguided attempt to exterminate rats. However, rats are largely nocturnal, or active at night, and the mongoose is diurnal, or active during the day. This ill-conceived introduction has had devastating results for Hawaii’s ground-nesting birds, including three endangered species: the Hawaiian black-rumped petrel, the Newell’s shearwater, and the ne-ne or Hawaiian goose. The ne-ne was pushed to the brink of extinction by over-zealous hunting during the breeding season and by mongoose predation, but strict protective measures and captive breeding programs have increased its numbers. At present there are about 800 birds, and counting.

Domestic cat – Felis catus

While much effort has been made to curb the cat population through neutering and spaying, there are still more than 100 million domestic cats in the United States alone. It is thought that cats kill about 500 million birds, 1 billion small mammals, and 250 million lizards and other reptiles annually in North America. One study in Britain showed that the average number of birds killed by a free-ranging house cat was 40 per year, despite being well fed at home. Another study showed that bell-wearing cats actually caught more prey than un-belled cats. It is uncertain from the second study whether the cats actually become stealthier because of the bell, or whether only the most successful hunters are generally belled in the first place. Cats are just one of a growing list of pets that become a problem when they are irresponsibly or accidentally “set free.”

Miconia – Miconia calvescens

Tahitians call this Latin American transplant the “green cancer,” as it now covers nearly 70 percent of Tahiti’s forests. This beautiful plant’s leaves are velvety and have purple undersides. A mature tree can grow to fifty feet and casts such dense shade that very few plants can survive beneath it. Unlike native plants, miconia’s shallow roots do not hold the soil well. Runoff and siltation from large stands of miconia are contributing heavily to reef degradation. Like other successful invasive plants, miconia matures early and can produce millions of seeds a year. There are many vectors for the spread of these seeds: wind, water, bird droppings, and mud on grading equipment, bulldozers, autos, pigs’ feet, or hiking shoes. Some 200,000 acres of Hawaii are also covered with it at present, although intensive control and eradication efforts are underway. 

Starling – Sturnus vulgaris

Eugene Schieffelin was the leader of a Victorian society whose aim was to bring to America plants and animals that reminded its members of “home.” Schieffelin’s particular passion was for the birds mentioned by Shakespeare, so in the early 1890s, he released 100 starlings in Central Park in New York. The current population estimate for starlings is over 200 million, making this the most successful avian introduction to this continent. Starlings have adapted well to modern life, making use of buildings, dumps, and large-scale farming to great advantage. Unfortunately, they also tend to out-compete native birds for nesting cavities. Competition is heightened by the fact that there are so few remaining natural forests with standing dead wood. One of the benefits of the starlings’ great numbers is their ready availability as study subjects in the exploration of flight mechanics, flocking dynamics, and avian genetics.