Ecosystem Targets and Supporting Indicators
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The least tern (Sternula antillarum) is the smallest of American terns. They are migratory birds that winter in Central America, the Caribbean, and Northern South America. Breeding colonies appear along with either marine or estuarine shores of the coastal United States, or on sandbar islands in large rivers throughout the interior of the United States. The least tern hunts primarily in shallow estuaries and lagoons where small fish are abundant. Once they have spotted their prey, they plunge into the water in a spectacular aerial dive to catch it. The least tern’s favored nesting habitat is prized for human recreation, residential development, and alteration by water diversion, which interferes with successful nesting in many areas.
The abundance of least terns indicates whether there is sufficient protected beach habitat for coastal birds and sufficient food supply of forage fish in coastal waters.
Least terns, a threatened species in New York and Connecticut, live in large colonies on the beach and plunge into nearby waters for food. Predators, human disturbances, and tidal flooding can disrupt tern nesting sites, but the terns have the potential to recolonize in other beaches within a four-state region that includes New York, Connecticut, Rhode Island, and Massachusetts. The least tern population has remained relatively stable among the southern New England/New York region since 1990. In 2011, there were 7,078 least tern pairs in the region, 735 pairs above the 20-year average.
Since the dismal shorebird nesting season of 2018, in which only 62 pairs attempted nesting and only 14 least tern chicks fledged, the last three years of nesting least terns in Connecticut bounced back to 300 nesting attempts per year. It is currently not known why Connecticut experienced such a sharp decline in 2018. In 2020, 299 pairs fledged 71 young but, unfortunately in 2021, although 311 pairs nested, only 32 chicks fledged. Although the total number of least tern breeding pairs throughout the North Shore of Long Island had steadily increased from a low of 382 pairs in 2014 to a high of 996 attempted nests in 2018, the number of breeding pairs has been steadily decreasing over the past three years. But the steep decline in the least tern nesting success in Connecticut, and throughout the Northeast region, is being investigated by wildlife managers of a northeast multi-state Least Tern Working Group working with the US Fish & Wildlife Service (USFWS). During this same three-year period, New York numbers have consistently decreased while Connecticut numbers have stabilized. The data suggests that some birds may favor one side of Long Island Sound from year to year, depending on available habitat and storm-damaged areas.
In addition to the noted breeding pairs, productivity rates of those pairs is essential to the success of the species. In 2022, Connecticut’s most successful site, in West Haven, observed a productivity rate of 1.22. While this rate appears low least terns are long-lived birds and the Atlantic Coast population has remained stable. However, predation and/or human disturbance continues to be a problem at most breeding sites in Connecticut.