Ecosystem Targets and Supporting Indicators
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The least tern (Sternula antillarum) is the smallest North American. They are migratory birds that winter in Central America, the Caribbean, and Northern South America. Colonies breed throughout 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 habitats, sandy or shelly beaches, are 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 state 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.
Over the past 5 years, an average of 295 breeding pairs per year were observed in Connecticut. This is a successful recovery from the dismal Connecticut shorebird nesting season of 2018, in which only 62 pairs attempted nesting and only 14 least tern chicks fledged. It is currently not known why Connecticut experienced such a sharp decline in 2018.
Although the total number of least tern breeding pairs throughout the North Shore of Long Island steadily increased from a low of 382 pairs in 2014 to a high of 996 attempted nests in 2018, the number of breeding pairs decreased over a three-year period from 2018 to 2021. During this same three-year period, however, Connecticut numbers stabilized. The data suggest 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 are essential to the success of the species. In 2023, Connecticut’s most successful site, in Groton, observed a productivity rate of 0.67. 2024 was another year of low productivity in Connecticut. However, the adult count has remained relatively steady throughout the Atlantic Coast population. Least terns are a long-lived species where adult survival is more important than high productivity. The steep decline in the least tern nesting success 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). Threats to adult and chick survival include predation and/or human disturbance, such as off-leash dogs. These threats continue to be a problem at most breeding sites in Connecticut and New York. A Connecticut State law (Public Act 23-155), “An Act Authorizing the Establishment of a Seabird and Shorebird Protection Program”, provides extra protection from these threats to vulnerable beach-nesting species, including Least Terns.
Read more about Least Terns on CT DEEP and USFWS. Photo by Paul Fusco.
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