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Science Watch

Foreign Animal Species

Dr. Stephen Zawistowski, Ph.D., Sr. VP Animal Sciences, ASPCA

SCIENCE WATCH - Strangers in a Strange Land

“I’ll have a starling shall be taught to speak nothing but ‘Mortimer,’ and I’ll give it to him to keep his anger in motion.”
—William Shakespeare, Henry IV

In the early 1890s, Eugene Schieffelin released dozens of European starlings in New York City’s Central Park. A transplanted Englishman, Schieffelin intended to introduce all of the birds mentioned in Shakespeare’s works. We can only be thankful that he didn’t!

In many ways, the starling is the poster child for the invasion of foreign species. Their introduction has had enormous consequences for native birds. Aggressive and cosmopolitan, starlings thrived in both urban and rural settings, and by the early 1900s, they were among the most common bird species in eastern North America. By 1950, they were well established throughout the continent, outcompeting native species for food and nesting sites. In many regions, to help reestablish natives such as blue- birds, it has taken exceptional efforts to provide nest boxes that exclude starlings.

Coming to America

Invaders have arrived in America by intent and by accident. While few people hold the starling in great esteem, some introduced species have established themselves in both the environment and the American psyche. The wild mustangs of the American West, for example, are descendants of the horses originally brought to America by Spanish explorers. These horses changed the culture of Native Americans by enhancing mobility for hunting, trade and warfare. They are now as much a part of the Western range as any native species.

State conservation departments have introduced a wide variety of species to America and have transplanted native species to different regions - often with unforeseen consequences. European brown trout introduced to American streams have shrunk the range of native brook trout in the East, while frequent transport and release of hatchery- raised rainbow trout is thought to be the source of whirling disease among rainbow trout in the West. Fish and Game departments working to reestablish their native fauna are frequently faced with undoing the past work of their own departments. In a truly ironic twist, the official state bird of South Dakota, the ring-necked pheasant, is not even a native species, but an import from China in the late 1890s.

The introduction of nonnative species is now seen as a dire threat to ecosystems. Many biologists rank species invasion on a par with habitat destruction as an extinction threat. This threat ranges from the preying by invaders on native species and competition for resources, to the introduction and propagation of new diseases and parasites that harm native species, to the depletion of rare gene pools through hybridization with native species.

Island species are especially vulnerable to the introduction of new predators. The natural dispersion of species to islands often depended on ocean currents and winds, thus favoring airborne animals or those small enough to float - which typically precluded most land predators. As a result, many island species have not evolved protection from such predators. In Hawaii, the Indian mongoose was introduced to control the rat, an invasive species that was damaging sugarcane fields. The mongoose eventually played a role in the decline of ground-nesting birds in the region. In Guam, the introduction of the brown tree snake from the South Pacific and Australia resulted in the loss of 10 of 13 native bird species. Cats, introduced to islands by sailors, have decimated many ground-nesting bird populations.

Costly Control

In addition to the biological costs, introduced species present an economic cost as well. European zebra mussels, probably introduced through the dumping of ballast water by a freighter in American waters, now clog water intakes in lakes, streams and reservoirs, requiring laborious and costly removal efforts. Mexican boll weevils and Africanized bees are among the many imports that impact agriculture.

Managing invasive species is problematic, because effective control plans often rely on trapping, hunting or other inhumane methods. Limiting the influx of additional nonnative species is also needed. Public education on the dangers of bringing in plants and animals from other countries and regions, rapid responses before introduced populations grow out of control and increased oversight of intentional introductions by government agencies all need to be part of the effort.

Dr. "Z" is senior vice president of ASPCA Animal Sciences and Animal Watch science advisor.

Courtesy of
ASPCA
424 East 92nd St.
New York, NY 10128-6804
(212) 876-7700
www.aspca.org

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