The common starling (Sturnus vulgaris) is now classified as a highly invasive species in North America. Originally native to Europe and parts of Asia, its widespread presence in the Western Hemisphere has raised significant ecological and economic concerns. This article explores the reasons behind the common starling’s success as an invasive species, from its historical introduction to its biological advantages and subsequent impacts on native ecosystems and agriculture.
Unintentional Arrival and Spread
In 1890, approximately 60 common starlings were deliberately released in New York City’s Central Park by Eugene Schieffelin, a member of the American Acclimatization Society. He reportedly aimed to introduce all bird species mentioned in William Shakespeare’s works to North America. While other attempts at introduction had largely been unsuccessful, the Central Park population thrived.
The common starling population rapidly expanded its range across the continent. By 1928, the species had established itself firmly across states from the Atlantic to the Mississippi River, and into parts of Canada. Today, an estimated 93 million to 200 million common starlings range from Alaska to Mexico.
Key Biological Advantages
The common starling possesses several biological traits that contribute significantly to its success as an invasive species. One advantage is its high reproductive rate, characterized by multiple broods per year and large clutch sizes. A breeding pair can produce two clutches of four to six eggs annually, with fledglings leaving the nest within five to six weeks.
Common starlings are dietary generalists. Their omnivorous diet includes insects, fruits, seeds, grains, and even human refuse, enabling them to thrive in various environments. This adaptability extends to their habitat preferences, as they can flourish in urban areas, agricultural lands, and natural environments alike, often nesting in cavities within trees or artificial structures.
Their highly social behavior, forming large flocks, provides safety in numbers and facilitates resource domination. These large groups, sometimes numbering in the thousands, can quickly overwhelm food sources and nesting sites. Common starlings also exhibit aggressive behavior, especially during nesting season, which allows them to outcompete other birds.
Disruption of Native Ecosystems
The aggressive nature and rapid proliferation of common starlings lead to significant disruption within native ecosystems. They are cavity nesters, which directly puts them in competition with native cavity-nesting birds, such as bluebirds, woodpeckers, and purple martins.
Common starlings are known to aggressively outcompete native species for these limited nesting sites, often evicting them or destroying their eggs and young. This competitive pressure can contribute to declines in native bird populations. Their large flocks can deplete food resources, making them less available for native species that rely on similar diets.
Economic Strain on Agriculture
The common starling’s invasive presence imposes a substantial economic burden, particularly on the agricultural sector. Large flocks are responsible for consuming and damaging valuable crops, including cherries, grapes, corn, apples, and blueberries. This damage can result in significant financial losses for farmers, with estimates reaching hundreds of millions of dollars annually in the United States.
Starlings also consume and contaminate livestock feed, leading to further economic losses for agricultural operations. A flock of 1,000 starlings can consume approximately 1.5 tons of cattle feed over 60 days during winter. Common starlings can act as vectors for diseases such as salmonellosis and transmissible gastroenteritis (TGE), which can spread to livestock and humans, incurring costs for prevention and treatment. Their droppings can also cause damage to buildings and machinery, adding to the overall economic strain.