European Starlings (Sturnus vulgaris) are a highly recognizable bird species, particularly in North America, where they are widely regarded as invasive. Native to Europe, these stocky, dark birds were introduced to new environments and have since thrived, often at the expense of native wildlife.
Their Journey to New Lands
European Starlings were deliberately introduced outside their native range, most notably in North America. In 1890, Eugene Schieffelin released 60 starlings in New York City’s Central Park, followed by 40 more in 1891, aiming to introduce all birds mentioned in Shakespeare’s works. While earlier attempts in other states were unsuccessful, these New York City introductions proved viable, leading to rapid spread. From these initial releases, the starling population exploded, now estimated at 93 million to 200 million across North America, from Alaska to Mexico.
Traits That Enable Invasion
European Starlings possess several biological and behavioral characteristics that have allowed them to become successful invasive species. Their adaptability to various habitats, including urban, suburban, and rural areas, gives them a broad ecological range. They exhibit dietary flexibility, consuming a wide variety of foods such as insects, seeds, and fruits, which enables them to exploit diverse food sources across seasons.
Starlings also demonstrate a high reproductive rate, contributing to their rapid population growth. A breeding pair can produce two broods per year, with some even raising three, particularly in warmer southern regions. Each clutch typically contains 4 to 6 eggs, which hatch after an incubation period of about 12 days.
Their aggressive nesting behavior gives them a significant advantage over native birds. Starlings are secondary cavity nesters, meaning they utilize existing holes in trees or structures, often evicting current residents. They aggressively compete for nesting sites, displacing native cavity-nesting species like bluebirds, purple martins, woodpeckers, and swallows. Males are particularly territorial, defending nest sites and sometimes destroying the nests or pecking holes in the eggs of competing species.
Social behaviors, such as forming large flocks, further contribute to their invasive success. Starlings are gregarious, gathering in immense flocks, sometimes numbering in the thousands, especially outside the breeding season. These large aggregations, known as murmurations, are thought to provide defense against predators. Their collective feeding and roosting habits allow them to quickly locate and exploit abundant food resources.
Ecological and Economic Consequences
The widespread presence of European Starlings has led to various negative impacts on both native ecosystems and human interests. Ecologically, their aggressive competition for nesting sites directly affects native cavity-nesting birds. Species like Eastern Bluebirds, Purple Martins, and various woodpeckers face displacement as starlings usurp their tree cavities and nest boxes.
Economically, European Starlings cause substantial damage to agriculture. They consume and damage a wide range of fruit crops, including apples, blueberries, cherries, grapes, peaches, and strawberries. This damage is not just from consumption; starlings also peck and slash at fruits, reducing quality and increasing susceptibility to disease. Annual agricultural losses attributed to starlings in the U.S. are estimated to be millions of dollars, with some reports suggesting figures as high as $800 million per year.
Beyond crop destruction, starlings pose problems for livestock operations. They gather at feed troughs, consuming significant amounts of livestock feed and contaminating the remaining supply with their droppings. For instance, 1,000 starlings can consume approximately 100 pounds of grain daily. This contamination can lead to economic losses by diminishing feed quality and potentially transmitting diseases.
European Starlings are also known carriers of various pathogens that can affect both livestock and humans. Their droppings can transmit bacteria such as Salmonella and Escherichia coli to feed and water sources, posing a risk to animal health and potentially to humans. Additionally, their droppings can harbor the fungus Histoplasma capsulatum, which can cause histoplasmosis in humans, particularly in areas with large roosts. The large flocks they form exacerbate these issues by concentrating waste and facilitating disease spread.