European starlings (Sturnus vulgaris) are a common bird species in North America, yet they are officially recognized as an invasive alien species across the continent. These stocky black birds feature short tails, triangular wings, and long, pointed bills. Their plumage shifts seasonally, appearing covered in white spots during winter and transitioning to a darker, glossy appearance in summer. Their presence stems from an intentional introduction, leading to significant ecological and economic consequences.
Arrival and Spread
The presence of European starlings in North America traces back to an intentional introduction in the late 19th century. Eugene Schieffelin, a Shakespeare enthusiast, introduced them to the continent. He released 60 to 100 starlings in New York City’s Central Park in 1890 and 1891.
Despite these relatively small initial numbers, the species successfully established itself. After a brief ten-year lag, they rapidly expanded across the landscape. Other early introductions failed, making the Central Park release crucial for their establishment.
From these few dozen birds, the population exploded, rapidly colonizing vast new territories. Within decades, European starlings had spread across the entire continental United States and into Canada and Mexico. Today, their range extends from Alaska to Mexico, with an estimated population of 93 million to over 200 million individuals. Their swift colonization from a small founding group demonstrates their capacity for dispersal and adaptation.
Traits That Fuel Their Success
European starlings succeed as an invasive species due to several biological and behavioral traits. Their exceptional adaptability allows them to thrive across a wide range of habitats, from urban centers and suburban areas to agricultural fields and rural landscapes. They readily utilize diverse environments, including those with colder temperatures and arid conditions, adapting to new climates.
European starlings are highly opportunistic and generalist feeders, consuming both animal and plant matter. Their diet primarily includes insects and other invertebrates when available, which they extract from the soil. They also consume fruits, grains, seeds, and livestock feed, exploiting varied food resources throughout the year.
Their aggressive nature, particularly during the breeding season, is another significant factor in their proliferation. Starlings are fierce competitors for cavity nesting sites, often forcefully displacing native birds by taking over nests, destroying eggs, or even killing occupants. This combative behavior provides them with an advantage in securing prime nesting locations.
European starlings exhibit a high reproductive rate, typically laying 4 to 7 eggs per clutch and often producing one to two broods annually. Their short incubation period of 11 to 13 days and rapid fledging time contribute to their prolific breeding success. Their high fecundity, combined with communal roosting and foraging, allows them to maintain substantial populations and exploit resources.
Broad Impacts
European starlings exert wide-ranging negative impacts across ecological, agricultural, and public health domains. Ecologically, their aggressive nature poses a threat to native bird species, particularly those that rely on tree cavities for nesting. Starlings fiercely compete for these limited nesting sites, often usurping nests from native birds like eastern bluebirds, northern flickers, and various woodpecker species. This competition can involve destroying eggs or even killing the young of other species to claim a cavity. Some studies indicate declines in specific native cavity-nesting species like sapsuckers and northern flickers due to starling interference.
In agricultural settings, European starlings cause substantial economic losses for farmers. Their large flocks target a variety of crops, including fruits and grains. Starlings not only consume these crops but also peck at them, rendering produce unmarketable and more vulnerable to diseases and pests. Annual agricultural damage in the United States attributed to starlings is estimated to be hundreds of millions of dollars.
Beyond crops, starlings also impact livestock operations. They frequently raid feedlots, consuming significant quantities of expensive animal feed and contaminating the remaining supply with their droppings. This contamination can reduce the feed’s nutritional value.
From a public health and safety perspective, European starlings present several concerns. They are known carriers of various pathogens, including various bacteria and fungi. These can be transmitted to humans and livestock through contaminated food, water, or direct contact with fecal matter. The fungus associated with large bird roosts can cause histoplasmosis, a respiratory disease.
Furthermore, the communal roosting habits of starlings create aviation hazards. Large flocks near airports can lead to dangerous bird strikes, where birds are ingested by aircraft engines.