Ecosystem Targets and Supporting Indicators

Least Terns

The least tern is the smallest of American terns. They are migratory birds that breed along marine and estuarine shores of the United States. Their abundance indicates the quality of coastal habitat and quantity of forage fish available for food.

View Implementation Actions for Least Terns

Show/Hide Table Data

Least Terns (Breeding Pairs)
CTNYTotal
1991627-
1992655-
1993175-
1994334-
1995538-
1996461-
1997403-
1998447-
1999335-
2000239541780
20011758281,003
2002224767991
2003197650847
2004158548706
20052468241,070
20061441,2111,355
2007147691838
20082521,0731,325
200990843933
20101191,0001,119
20113599541,313
2012350585935
20135308331,363
2014257382639
2015241407648
2016250526776
20172449111,155
2018629961,058
20192989041,202
20202997591058
2021311459770
2022247737984
2023329441770
4-State Least Terns (Breeding Pairs)
MANYCTRITotal
1992264224606552125969
1993262230331751756005
1994261725473342165714
2995275635205381356949
1996267330934612786505
1997319425604032626419
1998308524854475256542
1999341622613352976309
2000326721032392725881
2001342127391751906525
2002279632672241726459
2003249626781972395610
2004269120691582485166
2005265733822462146499
2006261527981442105767
2007311027921472356284
2008377636692522157192
200935692817901186594
2010348428321196437078
2011430926223591837473

WHAT IS THE LEAST TERN?

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.

WHAT DOES THIS INDICATE?

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.

STATUS

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, in recent years the number of least tern nesting pairs in Connecticut bounced back to at least 200 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 decreased over the a three year period from 2018 to 2021. 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 2023, Connecticut’s most successful site, in Groton, observed a productivity rate of 0.67. 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, such as off-leash dogs, continues to be a problem at most breeding sites in Connecticut.

DATA NOTES

  • The New York dataset for this indicator includes monitored sites on the North Shore of Long Island (Long Island Sound) and additional sites in Peconic Bay and Shelter Island in the North Fork of Long Island. LISS assesses this entire sub-region of Long Island for the least tern indicator because the birds frequently re-nest and might move from a Peconic Bay or Shelter Island beach to a Long Island Sound beach and back in the course of a year. LISS also maintains the same dataset for its other beach-nesting indicator, piping plovers.
  • New York data from 1990 to 2001 is currently not available.
  • Due to restrictions related to Covid-19, surveys were limited in 2020.

Data Sources

  • Connecticut Department of Energy and Environmental Protection-Wildlife Division
  • New York Department of Environmental Conservation- Division of Fish and Wildlife
  • Massachusetts Department of Environmental Protection- Division of Fisheries and Wildlife
  • Rhode Island Department of Environmental Management- Division of Fish and Wildlife

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