In the opening act of Henry IV: Part One, the eponymous king refuses to help free Lord Mortimer, the brother-in-law of his loyal knight Hotspur, from imprisonment, and even forbids Hotspur from mentioning Mortimer’s name in his presence. As revenge, Hotspur plots to “find him [the king] when he lies asleep, And in his ear … holla, ‘Moritimer,’” before changing his mind and deciding that, “Nay, I’ll have a starling … taught to speak nothing but ‘Mortimer,’ and give it to him to keep his anger still in motion.” 

It’s a strange plan, but it’s not as strange as the plan it inspired almost 300 years later, hatched by an eccentric New York businessman named Eugene Schieffelin.

Schieffelin was a pharmacist and drug manufacturer by trade, who also had a longstanding interest in wildlife and zoology. In the mid-1870s, he joined the New York chapter of an organization called the American Acclimatization Society. Founded in 1871, the Society sought to introduce European and Asian flora and fauna to the United States for various cultural, aesthetic, and economic reasons. Schieffelin became its chairman in 1877, and in the same year oversaw a meeting in New York in which it was proposed that every single species of bird mentioned in the works of Shakespeare should be imported and introduced to the city, so as to “contribute to the beauty” of Central Park. And, in light of Hotspur’s bizarre idea to troll the King of England in Henry IV: Part One, Schieffelin’s list included the European starling

Admittedly, a handful of similar attempts to introduce foreign birds to America had already been made by the time of Schieffelin’s idea. Some—most notably the house sparrow—had thrived, while others—such as the skylark, the song thrush, and the bullfinch—had faltered, and their highly localized populations remained low. Even an earlier effort to bring the starling to U.S. in 1876 didn't take as the American Acclimatization Society had hoped. The second attempt, however, outdid everyone’s expectations. 

Schieffelin began by releasing 60 starlings into Central Park in 1890. Concerned that their population was failing, the following year he released another 40 individuals, and soon their numbers began to swell. News of the first breeding pair, spotted on the eaves of New York’s American Museum of Natural History, was widely celebrated across the city, but for the first six years the birds refused to spread beyond Manhattan. Once they did, however, their population flourished. 

The starlings’ characteristically hardy and adaptable nature, and their willingness to eat practically any food available, allowed them to make the most of all environments they encountered. Within just 30 years, they had extended their range south as far as Florida, and inland as far as the Mississippi; by 1942, they had reached the West Coast; they quickly spread north into Canada, and eventually reached Alaska; and today they can even be found all along the Mexican border. By the 1950s, it was estimated that there were around 50 million individual starlings in America, but despite attempts to poison them, electrocute them, glue them, grease them, and even coat them in itching powder, today that number is closer to 200 million—all descended from Schieffelin’s original flock of 100 birds.

Predictably, the starling’s introduction to America and the subsequent explosion in its population was not without its consequences. Native species that now faced new and unexpectedly voracious competition from the starlings for food and nest sites suffered as a result, and, while the starlings thrived, the native birds' populations collapsed. Today, the starling is still widely considered an invasive and highly destructive pest all across America—and all because of a single line of text, written by Shakespeare more than four centuries ago.